ARMATURE WINDING-Moreton-Dunlap Drinkall ENGIN. LIB. TK 2477 M84 19441 (TUSK B 1,303,798 FORE US ARMATURE WINDING MORETON-DUNLAP DRINKALL at SURA------ DOPES AUTAT, IZINCHLIESSE CA maka katika JANGAN maakte formkebayatanjetivarit e angphany e qarkun mängdõigused gitaikydamaja, hipotiruumak ARDAN 1817 AISIN ARTES LIBRARY UNIVERSITY OF MICHIGAN | VERITAS SEMURIBE'S UNUS TUEBOR SCIENTIA OF THE SI QUERIS ·PENINSULAM AKONAM CIRCUMSPICE 12378373789.SASABIA COLLEGE OF ENGINEERING FÍALFISKEBABUS ··· U_N_E}/9/9). WIE BUBUBING HEISMEKAITAJALETITEINDENIYUG 1 I : 1 Engin. Library ! .} 1 TK 2477 M84 1944 1 2 THEM MAMMA Men bita Lab Lite WINDING STATOR OF 40,000 KW. 257 R.P.M., 60-CYCLE, 13,800 VOLTS ALTERNATING-CURRENT GENERATOR TO BE USED AT BOULDER DAM Courtesy of Allis-Chalmers Mfg. Co. Armature Winding A Practical Manual on the Construction, Wind- ing and Repairing of A. C. and D. C. Motors and Generators, together with Practical Connection Diagrams BY DAVID P. MORETON, B.S., E.E. Professor of Alternating- and Direct-Current Machinery, Illinois Institute of Technology Member, American Institute of Electrical Engineers and CARL H. DUNLAP Head, Electrical Engineering Departinent, American School Associate Member, American Institute of Electrical Engineers and L. R. DRINKALL, E.E. Head, Electrical Department The Wm. Hood Dunwoody Industrial Institute ILLUSTRATED AMERICAN TECHNICAL SOCIETY CHICAGO, U. S. A. 1944 · Copyright, 1920, 1923, 1929, 1937, by AMERICAN TECHNICAL SOCIETY COPYRIGHTED IN GREAT BRITAIN ALL RIGHTS RESERVED Reprinted 1940 Reprinted 1942 (With changes and additions) Reprinted January, 1944 No portion of this book may be reproduced by the mimeograph process or by any other proc- ess without permission from the publishers. THIS BOOK IS COMPLETE AND UNABRIDGED It is printed on light-weight paper in con- formity with government regulations for conserving paper pulp. Printed in the U. S. A. C INTRODUCTION WITH WITH the discovery of electromagnetism as a source of energy, electrical science progressed from an interesting phenomenon to the beginning of modern industrial development. Picture the world today without the dynamo, the electric light, electric cars, the telephone, the wireless telegraph, or the radio. In a few short years this progress has been made, and with the present knowledge of electrical science, what may not be done during the lifetime of present scholars and experimenters? As the armature, with its windings of insulated wire, is the heart of the whole system of electrical energy, this phase should receive special study. And it is with the purpose of showing the practical and theoretical considerations due the subject of armature winding that this volume has been prepared. For many years only an inkling of the principles of electrical energy was known. From time to time discoveries, the result of experiment rather than of calculation, led inventors nearer and nearer to one hundred per cent in electrical efficiency. Long ob- servations of electrical effects led to more or less empirical formulas, which have been corrected from time to time as additional obser- vations corrected original impressions. Advances in mechanical and chemical processes have aided in making electricity the willing servant of mankind, until today the weight of the water in the moun- tain stream traveling from the far-off hills to the distant sea becomes, through the armature of the dynamo, the energy which lights our cities, turns the wheels of industry, and carries our messages around the world. The development of the armature has thus had much to do with bringing about this happy condition in our economic existence. In preparing this volume the authors have drawn heavily upon their wide experience in the theoretical and practical design of electrical apparatus. Practically all of the line drawings have been drawn especially for this work, while the photographic reproductions represent the best practice of modern shops. Such advances have been made since present workmen were in school that it has become necessary for many to supplement school knowledge with information brought down to date. This volume is therefore particularly adapted for purposes of home study and self- instruction. The treatment of each subject will appeal not only to the technically-trained expert but also to the beginner and to the shop-taught practical man who wishes to keep abreast of modern progress. Without sacrificing any of the essential requirements of thorough practical instruction, the authors have avoided many of the heavy technical terms and formulas of higher mathematics, producing a book in clear and simple language on this important branch of electrical work. The text material in this book is also included in the cyclopedia "Applied Electricity." I 解 ​42 -1321 CONSTRUCTING A DIRECT-CURRENT GENERATOR The compensating field winding is placed in slots cut in the face of the main shunt and series field pole pieces. Courtesy of Westinghouse Electric and Manufacturing Co. CONTENTS Types of alternating-current generators. Frequency of alternating current Phase Power factor. Types of windings. Construction of alternators. · • Revolving field alternator.. Slow-speed engine-driven generators. Diesel engine generators. Turbo-generators Water-wheel generators Motor generators High-frequency generators.. Types of alternating-current motors. Armature construction.. Commutator and brush construction.. Armature winding. Direct-current armatures. Ring armatures. Drum armatures · • Speed of alternating-current motors. Single-phase motors. Atkinson motors. Repulsion-start induction-run motors.. General electric repulsion-induction motors Century repulsion-induction motors. Wagner repulsion-induction motors.. Delco repulsion-induction motors... Classification of fractional horsepower motors. Polyphase motors.. • Repairing mechanical parts of motor. Repairing field coils... • 1 Page 11 11 15 21 21 30 33 37 38 40 43 45 47 49 49 51 63 64 67 69 70 73 74 74 87 100 117 117 117 119 157 166 Direct-current armatures (continued) Repairing armature.... Repairing commutator Alternating-current motors and generators Magnetic fields.... Types of coils..... Winding single-phase motors... Winding polyphase induction motors. Winding alternating-current generators. Testing windings.. Locating motor troubles. Repairing windings. Connection diagrams for induction motors Index.... WT WE BE YOU Page ... 172 ... 186 . 191 194 199 202 ... 213 224 227 248 249 257 285 A CRAFTSMAN REMOVING COPPER BURRS AFTER MACHINING THE V-RING OF A COMMUTATOR FOR 5,000 HORSEPOWER MOTOR Courtesy of Westinghouse Electric and Mfg. Co., East Pittsburgh, Pa. ARMATURE SPIDER COMMUTATOR KEY COMMUTATOR SLEEVE COMMUTATOR MICA V RINGS COMMUTATOR BARS COMMUTATOR METAL V RING FRONT INNER BEARING CAP BEARING LOCK WASHER BEARING LOCK NUT FRONT OUTER BEARING CAP BEARING ASSEMBLY SCREW BRUSH YOKE BRUSH STUD INSULATION FIELD COIL BRUSH HOLDER STUD BRUSH HOLDER @ ww 720 777 720 07 EYE BOLT bio FRONT BEARING BRACKET ARMATURE LAMINATIONS FRAME ARMATURE COILS ARMATURE END PLATE BACK INNER BEARING CAP VELLUMOID GASKETS BALL BEARING BACK OUTER BEARING CAP ARMATURE SHAFT GREASE SEALS ARMATURE KEY A BALL-BEARING FULLY-ENCLOSED FAN-COOLED DIRECT-CURRENT MOTOR Courtesy of Reliance Electric and Engineering Company BACK BEARING BRACKET TYPES OF ALTERNATING- CURRENT GENERATORS The only difference between a simple direct-current generator and a simple alternating-current generator is that the direct-current generator has a commutator and the alternating-current generator has slip rings. From this slight difference in construction comes the difference in the voltage and kind of current obtained from the two units. FREQUENCY OF ALTERNATING CURRENT Frequency of an alternating current is the number of cycles the current passes through in one second. A complete turn of a loop of wire will make one complete voltage cycle as shown in Fig. 1. One- ONE ALTERNATION POSITIVE i180° ONE CYCLE ONE ALTERNATION NEGATIVE Fig. 1. Curve of Voltage Obtained from Revolving a Loop of Wire between a Pair of Poles 360° half the rotation of the loop will produce a voltage in a positive direction which causes current to flow out on the outside slip ring, and the next half turn completing the revolution will cause the out- side ring to be negative. This shows that the current flows equally in both directions during a cycle. A reversal of current is called an alternation. Two alternations make one complete cycle. 11 2 TYPES OF ALTERNATING-CURRENT GENERATORS Speed and Number of Poles. If this coil had rotated by two pairs of poles, the effect would have been just the same, as a coil making two complete turns with one pair of poles. Each time a coil or group of coils together pass a pair of poles a cycle is made. Obviously the speed and the number of poles will affect the fre- quency. Mathematically, frequency equals the poles times the revolutions per second divided by two and is often expressed as follows: Fig. 2. If the pole pieces were rotated and the coils remained stationary, the frequency would be exactly the same as it is with the revolving CYCLE Frequency= mit 360° WW CYCLE -IN CYCLE r.p.m. Xp I CYCLE 60×2. 14 CYCLES IŹ CYCLES CYCLES mit 2 CYCLES 720° Curve Showing Variation of Voltage When Loop Makes Two Complete Turns or Two Pairs of Poles Are Used loop. A pair of poles passing a coil produce two alternations or one cycle, and the coil passes through 360 electrical degrees. If this had been a 4-pole machine, two complete cycles, Fig. 2, would have oc- curred on the coil or 720 electrical degrees. Each pair of poles adds a cycle to the loop for each revolution that either the coil or the poles make. Some small alternating-current generators use the revolving armature like a direct-current generator, but for two very important reasons the larger machines without exception use the revolving field in which the poles rotate. One important reason revolving fields are used is due to the fact that insulation stands up better if it is stationary, and the other is no sliding contacts for the large 12 TYPES OF ALTERNATING-CURRENT GENERATORS 3 • currents are necessary with revolving fields. Moving parts are also lighter with the latter arrangement. Fig. 3 shows the various posi- tions of the revolving loop with corresponding voltage produced in Fig. 2 for each quarter cycle. No voltage is produced at the first and third positions of the coil as the conductors are not cutting the flux in these positions as shown by Fig. 2. As the coil leaves the starting position, as shown in Fig. 3, the voltage gradually increases N S START S CYCLE IN N 2020 N N S Ź CYCLE S CYCLE Fig. 3. Loop Positions and Instantaneous Voltages Shown as a Single Loop of Wire Is Revolved in a Magnetic Field and the second picture shows the voltage at the highest point when the quarter cycle position is reached. SINE CURVE The sine curve shown in Fig. 1 is the standard of reference for all discussion on alternating current. This curve can be plotted graphically by using a sine table and the corresponding angles. The sine itself is simply the ratio of two sides of a right-angled triangle, being the altitude divided by the hypotenuse. The cosine referred to in power factor discussions is the ratio of the base to the hypot- enuse. Each angle always has the same sine value, likewise a cosine value which is always the same number for any particular angle. A curve plotted from the sine values would always have a maximum value of one. The sine curve, shown in Fig. 4, can be developed mechanically 13 4 TYPES OF ALTERNATING-CURRENT GENERATORS from a circle as follows: Starting with a point A at position O make a circle about a center C. Draw a horizontal line to the right of the circle from O to B and divide it into sixteen equal lengths. (For more accurate work, more divisions should be used.) This line re- presents the time it takes point A to go around the circle and is measured in degrees 0 to 360. Divide the circumference of the circle into the same number of divisions as there are in the horizontal line. A vertical line from each one of these division points on the cir- 8 10 5 || 4 -13 2 14 A. %%- 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 10 ·15 12 Fig. 4. Development of a Sine Curve from a Circle cumference to the horizontal line through C represents the value of voltage generated at this particular instant by the coil in passing through the pole flux. These lengths laid off vertically on the hori- zontal line will give points through which the sine curve can be drawn, as shown in Fig. 4. The voltage curves for generators do not conform to the sine wave usually pictured, but take shapes similar to those shown in Fig. 5. These shapes give better operating results and are used with practically all commercial machines. The shape of this voltage wave can be changed to any desired form by changing the contour of the pole face. In this figure the pole face is flat and the air gap uniform, which produces the wave form shown. If the pole face was changed slightly so as to weaken the flux density at the front and rear sides of the pole, the wave form would be more peaked and would look more like the sine wave. The wave form shown in Fig. 5 is made by a single coil in the armature slot. Commercial generators ordinarily have more than one coil per slot so the wave form is not quite so flat topped but is more like the sine curve. 14 TYPES OF ALTERNATING-CURRENT GENERATORS 5 PHASE The term phase, as used in electrical work and in literature, has two separate and distinct meanings. Unless these are clearly and definitely understood a great deal of confusion may result. One E 1 K Fig. 5. S NEGATIVE VALUES of E.M.F. E E ----E--: ARMATURE/CORE E N E POSITIVE VALUES OF E.M.F. IN TO EXCITING FIELD COILS E ONE CYCLE OR TWO ALTERNATIONS Development of Magnetic Fields and Voltage Curve Obtained from Them S E meaning of the term phase has to do with circuits. Single-phase, two-phase, three-phase, and six-phase circuits are frequently men- tioned in discussing alternating-current circuits. A single-phase circuit may be defined as one which has voltage S N I AXIS OF TIME NEGATIVE VALUES OF E.M.F. E E Fig. 6. A Single-Phase Alternator with a 4-Pole Revolving Armature. Phases are determined by windings and not by the number of poles 15 6 TYPES OF ALTERNATING-CURRENT GENERATORS A impressed upon it from only one alternating-current source. single wire or coil revolving in a magnetic field will produce a single- phase circuit. The revolving coil shown in Fig. 3 would be a single- phase generator. The number of turns or the number of loops would A VOLTAGE START ……………………… 141 ** 1031 S Fig. 7. Elementary Two-Phase Generator PHASE I CYCLE w+ N ………… ... not change the phases which are also independent of the number of poles as shown in Fig. 6. Although this machine has four poles and two loops, it is only a single-phase generator, as there is only one voltage wave acting on any circuit connected to the slip rings. Ź CYCLE M PHASE 2 CYCLE N B Li T 繩 ​I CYCLE 1/ CYCLES 1½ CYCLES S CYCLES Fig. 8. Voltage Waves Generated by Two-Phase Generator A Two-Phase Voltage Curve 2 CYCLES A two-phase circuit in reality is two separate single-phase circuits, each with its own voltage wave impressed upon it. These two equal voltage waves are 90 degrees apart and always maintain this relationship. Fig. 7 shows a simple two-phase generator with the two separate windings 90 degrees apart rotating on the same shaft. This also shows the required two sets of slip rings and the 16 TYPES OF ALTERNATING-CURRENT GENERATORS 7 independent circuits 1 and 2 having absolutely no electrical con- nection with each other. The voltage waves produced by this gen- erator are shown in Fig. 8. These are 90 degrees apart at the start and always maintain this relationship because the coils in the VOLTAGE B 2 + 3 5 6 generator generating the electromotive forces are set at the same angular displacement and cannot shift position. A three-phase circuit is one in which three separate equal voltage waves are impressed 120 degrees apart on three circuit voltages. These may function on six wires but three wires ordi- narily make a three-phase circuit. Fig. 9 illustrates a three-phase Fig. 9. Elementary Three-Phase Generator with All Six Leads Brought Out ہوا N PHASE I S INSTANTANEOUS VALUES PHASE 2 PHASE 3 De 2 CYCLES -~ •14 Fig. 10. Voltage Waves Generated by a Three-Phase Generator-A Three-Phase Voltage Curve generator with all leads brought out to six-slip rings making a six- wire three-phase circuit. This is in reality three separate single- phase machines operating in the same magnetic field which makes all voltages equal. These circuits are often referred to as phases A, 1 B, and C especially in line work and armature winding in order to 17 8 TYPES OF ALTERNATING-CURRENT GENERATORS keep connections in correct order. The voltage waves shown in Fig. 10 show the relationship and position of the various voltages in a three-phase circuit. Because of the 120-degree spacing of the coils on this generator, all three voltage curves remain this same distance apart as shown in Fig. 10. A three-phase circuit has this particular characteristic. The instantaneous value of the voltage on one phase will be exactly equal to the algebraic sum of the voltages on the other two phases. Take the point where phases 1 and 3 cross below the line. B N CHITE S Fig. 11. Three-Phase Generator with Usual Internal Connections and Three Leads Brought Out Measure this distance, and it will be found to be just half the distance to phase 2 above the line. This means that the sum of the two nega- tive voltages on phases 1 and 3 will just equal the positive voltage on phase 2. All other points will give identical results at any position checked. Because of this voltage condition on a three-phase circuit, the coils can be connected together inside the generator making only three slip rings necessary as shown in Fig. 11. This arrangement of coils enables each line to be a part of two phases as shown by A, B, and C, and each ring serves two coils in the generator which is standard in winding practice. The other meaning of the term phase has to do with current and voltage relations within the circuit itself. When a load having ohmic resistance only is connected to a source of alternating-current voltage, the current wave will follow the voltage wave instantly, which means that current will be zero when the voltage is zero and reach a maximum value when the potential is at the peak, as shown by the curves in Fig. 12. The current and voltage are said to be in phase when this relationship exists. 4. 18 TYPES OF ALTERNATING-CURRENT GENERATORS 9 A very few alternating-current electrical circuits have only ohmic resistance opposing the flow of current in them. Inductance or capacity, and in some cases both, are present along with the ohmic resistance to limit the flow. Inductive reactance is caused by the magnetic effects set up when alternating current flows in 0° VOLTAGE CURRENT Fig. 12. Voltage and Current in Phase in a Single-Phase Circuit 360° INDUCTANCE ooooo 10° VOLTAGE Fig. 14. ance Choke Coil and Resist- in Single-Phase Circuit Producing Effect Shown in Fig. 13 PHASE ANGLE coils with an iron core such as are found in transformers, motors, and choke coils. This inductive effect from the alternating magnetic field acts like counter electromotive force on the flow of current and delays the time when it reaches a maximum value. Whenever this condition exists in a circuit, the current is said to be lagging behind the voltage and is out of phase as shown by Fig. 13. In this case the voitage and the current do not pass through zero or reach a maximum value at the same time. The current passes CURRENT Fig. 13. Voltage and Current Out of Phase in a Single-Phase Circuit 360° RESISTANCE through zero at a later time and reaches a maximum later than the voltage maximum. The angle between them, measured along the horizontal line between the points where the curves cross it, is called the phase angle between the current and the voltage. The cosine of this angle is the power factor for the circuit. Fig. 14 shows a choke coil in series with resistance connected to a source of alternating current producing the effect shown in Fig. 13. All three 19 10 TYPES OF ALTERNATING-CURRENT GENERATORS types of opposition to current flow, whether it is ohmic, inductive, or capacity, are measured in ohms. These combine differently in an alternating-current circuit than the ohms of a direct-current circuit. Inductive ohms and capacity ohms act at right angles to the resistance in the circuit when both are present. Fig. 15 shows three conditions which may exist in an alternating-current circuit. In Fig. 15 at A is illustrated the relationship existing in a circuit of the type shown in Fig. 14. The three sides of the triangle are made from the following: the base R is the ohmic resistance, the 4+ R R B Xc Z R A Fig. 15. Triangular Relations of A-Resistance and In- ductance; B-Resistance and Capacity; and C-Resis- tance, Inductance, and Capacity. These control the cur- rent flow in an alternating-current circuit XL-XC C altitude X is the ohms reactance due to the magnetic effect, and the hypotenuse Z is the impedance or actual resistance to the flow of current in this circuit. In all mathematical calculations involving Ohm's law in alternating-current circuits, the current is obtained by dividing the volts applied to the circuit by the impedance. Im- pedance in each case must be found from the triangle developed in Fig. 15 at A, B, or C as the circuit conditions demand. In Fig. 15 B shows how capacity and resistance combine to control the current flow when capacity is present. C illustrates the combined effects on the impedance of a circuit having resistance, inductance, and reactance. The magnetic and capacity effects are 180 degrees apart and neutralize each other leaving only the difference to com- bine with resistance to form impedance. Because of this neutraliz- ing action between capacity and induction, it is possible to change the power factor of any alternating-current circuit. On account of these magnetic effects, capacity in the form of static condensers or synchronous condensers is used to correct poor power factor. The phase angle between the impedance and the resistance in Fig. 15 is the same as the angle between the current and the voltage in Fig. 13, because the current lag is caused by the same magnetic effect which determines the size of the angle & in the triangle. 20 TYPES OF ALTERNATING-CURRENT GENERATORS 11 POWER FACTOR Power factor is the ratio of true power to apparent power. It is the wattmeter reading divided by the apparent power. The appar- ent power is the product of the ammeter reading multiplied by the voltmeter reading. This division gives the power factor, because the triangle of real watts and apparent watts is similar to the impedance triangle shown in Fig. 15. The power triangle shown in Fig. 16 is made from the volts and amperes which are the apparent watts in the circuit and the watt- meter reading. The magnetizing power may be measured with a APPARENT POWER VOLTS × AMPERES WATTMETER READING TRUE POWER Fig. 16. Power Triangle of an Alternating-Current Circuit MAGNETIZING POWER REACTIVE COMPONENT · reactive meter or may be calculated from the two previous sets of readings in the same way that the sides of any right-angled tri- angle may be found. Or the angle may be found from a table of cosines, as the wattmeter reading divided by the apparent watts gives the cosine 6. A protractor is used to lay off the angle and the magnetizing power is determined. This is a graphic method often used as a check on mathematical calculations. The reason these triangles are similar is due to the fact that inductance in an alternating-current circuit divides the current and voltage into two components, one acting on the resistance to produce useful work, and the other acting on the reactance to overcome the magnetic conditions in the circuit shown in Fig. 14. TYPES OF WINDINGS An alternating-current generator is a machine used to produce alternating current. It is made with three different types of wind- ings to produce single-phase, two-phase, or three-phase current, de- pending upon what application is to be made of the power derived from the machine. Direct current is almost always employed for exciting the 21 12 TYPES OF ALTERNATING-CURRENT GENERATORS fields of alternating-current generators or synchronous motors. These direct-current exciters may be separately driven or mounted on same shaft as the alternator. Separately driven exciters are pref- erable, because they give more stable voltage conditions than the direct-connected machines. Exciters mounted on the same shaft with the main generator cause double the voltage variation with a change in speed as a separately driven unit, because an increase in speed will not only raise the alternator voltage but will increase the exciter current through the field. Thus a one per cent rise in speed STATIONARY ARMATURE COIL REVOLVING FIELD SLIP RINGS A.C. LINE DIRECT CURRENT FOR EXCITING FIELD + Fig. 17. Single-Phase 4-Pole Revolving Field Type of an Alternating-Current Generator with Only One Group of Coils will not only raise the alternator voltage one per cent but will at the same time increase the field one per cent which would make two per cent change on the main line voltage. Separately driven units are more flexible in a large plant as one exciter may be made to supply the field for one or more generators, or exciters may be op- erated in parallel with other direct-current machines doing the same service. Single-Phase Alternator. As explained in the earlier pages of this lesson, a single-phase alternator is made with but a single wind- ing in the part connected to the line and supplying power. The field may be made with any number of pairs of poles. Fig. 17 illustrates a single-phase, 4-pole, revolving field type of alternating- current generator. The moving parts of alternating-current ma- chinery are nearly always referred to as the rotor while the stationary part is called the stator. The slip rings supplying the field are connected to some source of direct current. There is but a single set of coils on the stator and hence only one source of voltage which 22 TYPES OF ALTERNATING-CURRENT GENERATORS 13 makes this machine a single-phase alternator. In many cases a three-phase generator is so connected that two-thirds of the coils are used for a single-phase machine. This arrangement will permit the machine to deliver 65 per cent of its three-phase capacity. Any machine operating as a single-phase alternator should be very carefully laminated throughout its magnetic circuit to reduce iron losses, and the pole shoes should have a heavy squirrel cage FAN BLADES POLE SHOE SQUIRREL CAGE WINDING FIELD COIL Fig. 18. A Partial Rotor Assembly Showing Method of Fastening Field Coils and Poles Courtesy of Electric Machinery and Manufacturing Company to Rotor winding provided to damp out the pulsating effects of the armature rotation. Fig. 18 shows a sectional view of a rotor with the squirrel cage winding in the pole shoe. These poles are assembled from their laminated punchings riveted together under hydraulic pressure. The squirrel cage or damper winding is welded on each side to insure a low resistance circuit completely around the rotor as this greatly increases the effectiveness of this type of winding. For the same kilovolt amperes output, single-phase generators are fully 65 per cent heavier than a polyphase generator of the same power factor, speed, and voltage. This makes them not only more expensive to build, but increases all other investment costs. 23 14 TYPES OF ALTERNATING-CURRENT GENERATORS I Single-phase generators find application in electrochemical processes and some railway systems use single-phase power. Weld- ing transformers and electrical furnaces use single-phase generators, so power sometimes has to be supplied for these particular applica- tions where access to a power company line is not convenient. They also find some service in testing and experimental work. Single-Phase Two-Wire System. The single-phase generator connected to a line gives the two-wire system as shown in Fig. 17. As alternator voltages are usually higher than secondary distribu- tion voltages, a transformer is required between the generator and the load. The voltage used on a two-wire system is usually 110 volts and alternators generate 220, 440, 1300, 2300, 4000, 6600, + + +1 115 V 115 V 230V Fig. 19. Edison Direct-Current Three- Wire System A 13,200 and a few 33,000 volts. The transformer ratio to produce 110 volts on the line will depend upon the voltage at the source. Single-Phase Three-Wire System. The single-phase three-wire system has the same advantages for alternating-current systems as obtained with the three-wire direct-current systems discussed in Lesson 28. It is usually obtained on an alternating-current line by using a center tap on the secondary winding of the transformer. This method of obtaining the three-wire system has the added ad- vantage of being able to handle any amount of unbalance there might be, whereas, the balancer systems are definitely limited in ability to handle over a certain per cent of unequal load. Edison System. The Edison three-wire system for direct cur- rent was originally developed and used by Thomas A. Edison. He connected two 2-wire generators in series and connected the middle wire to the center point of the two machines as shown in Fig. 19. This arrangement provided two voltages, one for light and the other for power and, at the same time, cut down transmission losses. Any Z 24 TYPES OF ALTERNATING-CURRENT GENERATORS 15 amount of unbalance in the load is taken care of without additional equipment. However, too much unbalance causes an excessive. voltage on the side of the line with the smaller load. A similar system is used for alternating current from taps on transformer windings. Two-Phase Alternator. The two-phase generator is exactly like the single-phase alternator except that it has two separate windings on the stator. These windings make two entirely separate electrical circuits which have no connection with each other. The second winding, phase two, is spaced exactly between the coils on the 1 S 2 2 PHASE NO. I PHASE NO.2 Fig. 20. Two-Phase 4-Pole Revolving Field Type of an Alternating-Current Generator with Only Two Groups of Coils generator in Fig. 17. With the poles in the position shown in this figure, the voltage on phase 1 would be at a maximum as illustrated by the voltage at the start in Fig. 8. At this instant the voltage on phase 2 is zero because the pole flux is not cutting the coils on this phase at this instant. The position of the poles one-eighth of a revolution later, Fig. 20, indicates that the voltage on phase 2 is maxi- mum and phase 1 has decreased to zero. This condition is shown in Fig. 8 at point marked 1/4 cycle. Because these curves are 90 electrical degrees apart and always remain in this relative position, the two- phase system is sometimes called the quarter-phase system, this being just one-fourth of a cycle which is 360 degrees. Four-Wire System. An inspection of Fig. 20 shows four wires required to complete each of the circuits for the two phases. Whether these circuits are used for supplying power for lights or motors, they 25 '16 TYPES OF ALTERNATING-CURRENT GENERATORS are complete and independent throughout with the voltages remain- ing on the quarter-phase angle with reference to each other. Three-Wire Two-Phase System. The two-phase four-wire system may be converted to a three-wire system by making one line wire common to both phases or circuits. In order for this wire to handle the currents in both phases, the area of copper must be ap- proximately 41 per cent larger than either of the other two. The current caused by the common wire is exactly the square root of two which is 1.41 times the current in either outside line. The principal reasons for developing polyphase systems was 3 Canal 2 S 2 MADERERA 3 1 PHASE NO. I PHASE NO. 2 PHASE NO.3 Fig. 21. Three-Phase 4-Pole Revolving Field Type of an Alternating-Current Generator with Only Three Groups of Coils GRE for the use of electric motors and savings in transmission costs. The early single-phase motor would run, but no means was known for developing torque for starting. Primarily, to meet this situation, two-phase systems were put into use. As soon as the three- phase circuit was discovered, its numerous advantages over a two- phase circuit made it so popular that very nearly all power systems. changed over and the two-phase circuit has almost become history. Three-Phase Alternator. The three-phase alternator is made by adding another phase to the two-phase machine. The addition of another set of coils makes a considerable difference in the voltage relations as will be seen from an inspection of the voltage curves shown in Fig. 10. The two-phase voltages were 90 degrees apart while these curves are separated by 120 degrees, which relationship is always maintained due to mechanical arrangement of stator coils. 26 TYPES OF ALTERNATING-CURRENT GENERATORS 17 This three-phase relationship is obtained by winding three sets of coils on the stator. They are practically always spaced 60 degrees apart, and one group is reversed so that the electromotive forces will be separated by 120 degrees. In Fig. 21 is shown a three-phase stator with the necessary three groups of coils. These are spaced exactly 60 degrees apart and all six ends brought out for each circuit. The pole position with reference to the different phases will give instantaneous voltages shown at the start of Fig. 10. The instan- taneous voltage on phase two is at a maximum but is negative and is just starting toward zero, while the instantaneous voltages on phases one and three are both positive, but one is on the increase and three is already decreasing. This condition is explained from an inspection of Fig. 21. The two south poles are exactly under the coils in phase two producing a maximum negative voltage as shown by Fig. 10. The two north poles are partially over both phases one and three. As the rotor is revolving in a clockwise direction, the north poles are approaching phase one thus increasing the voltage positively, as shown in Fig. 10, and leaving phase three which causes a decrease in voltage as shown on the curve for phase three. The leads to phase one have been reversed, which changes the voltage relations in the three phases from 60 degrees to 120 degrees. Windings for two- and three-phase stators are never wound, as shown in Figs. 20 and 21, this plan being used for simplicity in showing the phase relations. Factory windings for these machines would place sides of different coils in the same slot where the currents in the two sides would be in the same direction, as this arrangement gives more effective use of the iron. The diagrams become involved and difficult for the beginner to follow and understand the volutions in the various phases. Six-Wire System. If all leads of the three-phase groups are brought out as shown in Fig. 21, six lines will be required and the system would be known as the six-wire system but would be only a three-phase system. This arrangement should not be confused with the conditions made by the windings of the ordinary three-phase alternator where six coil groups are used for each 360 magnetic degrees or pairs of poles. This coil arrangement would cause six different electromotive forces which would be 60 degrees apart or one-sixth of a cycle and would be known as a six-phase system. 27 18 TYPES OF ALTERNATING-CURRENT GENERATORS If, however, the coil leads are connected either star or delta and three leads connected to the load, the resulting currents will differ in phase by 120 degrees. Thus an alternator may be either a three-phase or a six-phase machine depending upon the connections to the load. Star-Connected-Four-Wire System. Figure 22 shows the coil groups in each phase connected together and the groups arranged at the 120-degree phase angle existing between each phase in the alternator shown in Fig. 21. Because of the fact that the instanta- RX oooooo 000000 A PHASE NO. I PHASE NO. 2 PHASE NO. 3 00000 PHASE NO. I PHASE NO.3 PHASE NO. 2 B Fig. 22. A-Schematic Diagram of a Three-Phase Generator and a Six-Wire System; B-Three-Phase Generator Windings Y-Connected, Forming a Three-Wire System neous value of voltage or current as shown by the curves in Fig. 10 is zero, each wire will act as a return for the other two. This makes possible the connection of the coil ends at the center of Fig. 22 at A which eliminates one wire from each phase and results in the wiring connection shown at B. A ground wire is frequently connected to the center tap and carried with the phase wires from the alternator through the whole distribution system. When this is done, the circuit is called the four-wire three-phase system. The star connections of the coils, shown in Fig. 22 at B, places two groups of alternator coils in series for a one-line phase at the angle of 120 degrees. This results in a higher voltage on the line by the square root of 3 or 1.73 over the electromotive force obtained from one group of alternator coils with the connections as shown at A. Thus the alternator would have a higher voltage output but a more limited current output with this connection, no gain in power being accomplished. The four-wire system of distribution permits an increased load on a three-wire line of nearly 75 per cent. Higher voltage trans- formers and motors may be used with resultant savings. Where this system has been tried, it has proved very satisfactory and ap- 28 TYPES OF ALTERNATING-CURRENT GENERATORS 19 parently no more hazardous with a good ground network than other grounded systems. A power company having a three-wire un- grounded system can, by increasing the generating capacity, chang- ing the transformer connections, and using the fourth grounded wire, increase the total load on the lines practically 75 per cent. Delta-Connected-Three-Wire System. Figure 23 shows the three coil groups for each phase in such a way that when they are joined ooo ooo o O o O o O o c 0 0 0 0 0 0 0 0 0 PHASE NO. I PHASE NO. 2 PHASE NO.3 llllllll llllllll 000000 PHASE NO. I PHASE NO: 3 PHASE NO.2 B A Fig. 23. Three-Phase Delta Connection-Six Wires and Three Wires A-Another Method of Showing a Three-Phase Generator Windings and a Six-Wire System; B-Three-Phase Generator Windings Delta-Connected, Forming a Three- Wire System together they form a triangle or circular arrangement. Since there. are 360 degrees in one cycle, this makes the three lines 120 degrees apart with reference to their phase relations. The delta connection gives the same voltage on each phase as the generator coil groups pro- duce, but it increases the current delivered to the line by the square root of 3 or 1.73 due to the phase relationship. The delta system is used extensively for transmission and dis- tribution work. This connection is frequently used in winding induc- tion motors as well as alternators. The power measured in kilovolt amperes is the same in an alternating-current generator regardless of the coil connection. With the star connection the voltage is higher by the square root of 3 and with the delta connection the current capacity is increased by the square root of 3 while the voltage remains at the single-phase value. Expressed mathematically, the power of the three phases of an alternator is: P-EI X √3, where P is the power, E the voltage, and I the current for each phase as shown at A, Fig. 22. In the three-phase star-connected arrange- ment shown at B, Fig. 22, this becomes P= (sq. root of 3) × EX I, where P is the three-phase power and E and I are the voltage and current the same as in the single-phase circuits. Power for the delta 29 20 TYPES OF ALTERNATING-CURRENT GENERATORS connection is given by the formula P=E × (sq. root of 3) × I and applies to B, Fig. 23. Thus power is the same from an alternator regardless of which connection is used, but the star or Y connection delivers higher voltage to the transmission while the delta connection raises the amount of current which can be supplied, the voltage re- maining the same as the single-phase potential. CONSTRUCTION OF ALTERNATORS Rating. The heating caused by the current in an alternator will determine its output. At normal voltage and normal current, a generator should not heat to a greater temperature than 40° C and should deliver its definite kilowatt rating at unity or 100 per cent power factor. Since the connected load determines the power factor at which the alternator must operate, its rating is usually given in kilovolt amperes, which is less than a kilowatt unless the power factor is unity. The rating if given in kilowatts is easily changed to kilo- volt amperes by dividing the kilowatts by the power factor. A machine with a rating of 100 kilowatts would become a 125 kilovolt ampere rating at 80 per cent power factor. Ratings are frequently given in kilovolt amperes at 80 per cent power factor on the name plate of the machine. Mechanical. Alternators may be made with revolving armature, where the generating coils rotate, or with rotating fields with the generating coils Stationary. Practically all commercial machines use the latter construction while a few small alternators are built with moving coils. These require all the power current to be picked up with brushes on slip rings and more difficulty is experienced in- sulating the higher voltages found on the generating coils. Lighter moving parts cut down vibration with revolving field types and make machines with less weight per unit of output, all of which accounts for the preference shown for revolving field alternators. The rotor or armature of the stationary field type of alternating- current generator is made by assembling laminations punched from special electric sheet steel. These punchings are varnished with special core varnish and assembled under pressure on a cast or steel spider to which they are securely fastened. Spaces are left when assembling to permit free circulation of cooling air. The coils on lower voltage armatures are wound with double-cotton or single- 30 TYPES OF ALTERNATING-CURRENT GENERATORS 21 cotton enamel magnet wire. These are then taped with cotton and oil linen tape, treated with waterproof and oilproof baking varnish, and dried in an oven at controlled temperatures. Slot insulation is made from a combination of insulating paper and varnished cloth. Fig. 24. An Alternating-Current Generator with a Direct-Connected Exciter Courtesy of Imperial Electric Company The coils are held in the slots with wood or fiber wedges which fit into dovetails in the teeth of the rotor. The collector rings for revolving coil armatures are made of special bronze in order to improve wearing qualities and have low contact drop at the brushes. These rings must be thoroughly in- sulated from the rotor spider and yet be securely fastened to it. Fig. 24 shows an alternating-current unit made in capacities from Fig. 25. Alternating-Current Winding on Rotor of Alternator (Right) and Direct-Current Armature of Exciter (Left) Mounted on Same Shaft Courtesy of Troy Engine and Machine Company 1 to 150 kilovolt amperes with an exciter unit mounted on the main shaft. Fig. 25 shows the rotor element with the direct-connected exciter unit. Note the heavy-duty slip rings and the wedges hold- ing the coils securely in the slots. Armature Windings. The most important of several factors. 31 22 TYPES OF ALTERNATING-CURRENT GENERATORS which affect the arrangement of the windings used on an alternator are: (1) wave shape; (2) coil distribution; (3) winding costs; and (4) efficient generation of voltage. Some other features, such as number of poles and frequency, will be determined by the speed to be used, and will also have their effects. on the armature windings. The wave shape should approximate the sine wave, which would mean coil distribution up to certain limits. In order to obtain the required distribution to produce the desired wave shape, the coils must occupy several slots per pole per phase. These may be a whole number, but it is not necessary as 112 slots per pole per phase may give a satisfactory wave form. Wave form is also frequently im- proved by using a fractional pitch winding. A fractional pitch wind- ing is one which spans fewer slots than the pole covers which would make the coil sides somewhat less than 180 electrical degrees apart. This sometimes is reduced to .66 and even .5. K Distribution of windings makes better ventilation possible and helps reduce leakage reactance as well as improve the wave shape. However this is limited, particularly on high voltage machines, as more insulation must be used between layers in slots and less room is available for copper. End turns must also be more carefully in- sulated. The cost of winding is an important item for consideration in constructing an alternator. Coils which can be formed and insulated before being placed in the slots very materially reduce costs and are better insulated. Form wound coils should all be the same shape. They require that the slots be open at the top, which reduces the efficiency of operation of the machine. However, these open slots may be closed or partially closed with magnetic wedges. Efficient generation of voltage requires that the winding must be arranged so there is very little bucking action present. To avoid this trouble, the coils must be very nearly full pitch, that is, the sides must be approximately 180 degrees apart magnetically. A careful analysis of the foregoing facts indicates that satis- factory winding of a machine will depend upon what is desired in the way of operating requirements such as wave form, efficiency and regulation as well as the first cost involved. Where conflicting vari- ables occur, a compromise must be made which best meets the re- quirements. If the alternator is wound with three-phase windings, • 32 TYPES OF ALTERNATING-CURRENT GENERATORS 23 these may be star- or delta-connected. In many cases there may be two independent groups of coils for each phase, especially with motor windings. Two sets of coils per phase make the machine easily converted into double normal voltage. A 220-volt connection can be made into a 440-volt winding by simply putting the groups in series. Figure 26 shows a winding diagram for an alternator having 18 Fig. 26. N rit T July S ++ ++ fr rtt πt THERE ARE IN T₂ T3 T Three-Phase Alternator Winding with 18 Slots, 18 Coils, 2-Pole Star- Connected slots with 18 coils two-pole star-connected. This makes 6 coils per phase and 3 coils per pole per phase. The pitch is full being 1 and 10. Phase 1 is shown in light lines, phase two in heavy lines, and phase three in broken lines. This is a very simple connection and is shown to give the idea of the winding layout. In practice more coils would be used and the coils would be placed with sides of different coils in the same slot, as current directions are such in three phase as to permit this practice. REVOLVING FIELD ALTERNATOR The revolving field alternator is built in all types including the belt-driven, high-speed direct-connected steam engine, slow-speed type, Diesel engine, turbo-generator, and the water-wheel type. 33 24 TYPES OF ALTERNATING-CURRENT GENERATORS Figure 27 shows a high-speed alternating-current generator made with either two or three bearings for belt drive or with one or two bearings where it is coupled to the prime mover. This unit is designed especially for use with oil, gas, or steam engine and built in capaci- ties ranging from 121/2 to 1250 kilovolt amperes 60-cycle with speeds from 514 to 1800 r.p.m. Note the open frame construction with the ducts at frequent intervals in the stator laminations. The air enters the machine through the end brackets, passes over the stator and field coils as well as through the stator core. This is accom- AIR DUCTS EXCITER D.C. TERMINAL COVERS FRAME A.C. TERMINAL COVER FEET- BEARING BRACKET OIL WELL COVER KEYWAY SHAFT OIL CUP Fig. 27. Westinghouse Type G Alternating-Current Generator with Ex- citer Mounted on End of Generator plished by an ample system of ducts and baffles which prevents recir- culation of the heated air. A sealed type of sleeve bearing, made oil, vapor, and dust tight, reduces bearing wear to a negligible amount. Stator. The stator frame of this machine is made of grey cast iron with the feet cast integral with the frame. The modern trend in all frame construction is toward rolled and welded steel frame construction. The core is built up with high-grade annealed steel sheet punchings dovetailed into transverse ribs in the frame. These laminations are compressed between end rings and keyed in place. The coils are form wound from double cotton covered wire with the slot portions wrapped with fish paper and mica. This in- sulation is not affected by heat or moisture, and age has very little deleterious or harmful effect on its insulating qualities. Every stator is given a radio frequency test which indicates insulation defects on 34 TYPES OF ALTERNATING-CURRENT GENERATORS 25 individual turns. In this way the factory knows that each machine is free from defective coils. This defeats the chief cause of electrical breakdowns. Fig. 28 shows the high-frequency test being given to a large stator in process of construction. IM Fig. 28. Testing Alternating-Current Windings with High-Frequency Alternating Current Courtesy of Electric Machinery and Manufacturing Company Rotor. The spider of the rotor is built up with steel punchings riveted together under hydraulic pressure. This core is then pressed and keyed to a steel axle shaft or a forged flange steel shaft for single bearing machines. The pole pieces are assembled from the electrical steel laminations riveted together under pressure. These poles are tightly dovetailed into rotor spider and keyed in position. The whole shaft and rotor is made with ample strength to withstand the variations in angular torque produced by Diesel engines. The field coils are wound with copper straps or rectangular double cotton covered wire. As these are wound, an application of 35 26 TYPES OF ALTERNATING-CURRENT GENERATORS insulating varnish is made to each layer and the whole coil is then impregnated with heat-resisting compound. Each coil is carefully insulated from the core and supports are provided to protect the coils against centrifugal forces and strains during operation. Fig. 29 shows a rotor used with the larger machines of this type. Note the damper winding provided near the pole faces to minimize hunt- ing and variations in speed of certain types of prime movers. This addition to the rotor winding is almost a necessity where gas or DAMPER WINDINGS FIELD COILS FIELD COIL LEADS SLIP RINGS FAN BLADES Fig. 29. Field Winding Mounted on the Rotor of a Large Alternator Courtesy of Westinghouse Electric and Manufacturing Company Diesel engines are used for motive power. Cast-iron collector rings are used almost exclusively on rotors magnetized from a direct- current source. Exciters for these alternators are usually mounted directly to the frame of the generator with the exciter armature mounted on an extension of the rotor shaft. This eliminates the necessity for exciter bearings. In applications where direct-connected exciters are not desirable, any method of drive may be resorted to. Dual drive is frequently used in larger power houses with motor drive a highly favored method. Gas, steam engine, turbo, and water-wheel units are frequently used to power exciters. There are a few installations where V-belts are used from the main alternator shaft to the exciter. 36 TYPES OF ALTERNATING-CURRENT GENERATORS 27 SLOW-SPEED ENGINE-DRIVEN GENERATORS The slow-speed generator is from necessity a massive piece of equipment with large weight per kilovolt amperes of output. Slow- speed machines require a larger number of poles to produce a given })), Fig. 30. Engine-Driven Type of Alternator. The Shaft and Bear- ings are Built as Part of the Engine Courtesy of General Electric Company frequency than is required with high-speed machines. In order to accommodate a large number of poles, the rotor diameter must be increased over what is required in more rapid moving elements. With slow moving field poles, larger sizes must be provided to furnish the magnetic flux necessary to generate the proper voltage. This leads to longer stator coils with increased iron in the stator. Figure 30 gives an excellent idea of a slow-speed alternating- 37 28 TYPES OF ALTERNATING-CURRENT GENERATORS current generator used in direct connection to a steam or Diesel engine. The open style frame provides ample opportunity for good ventilation. The end shields are die formed and thoroughly protect the windings without interfering with air circulation over the stator coils. A pole piece for this generator is shown in Fig. 31. The damper windings are located in the slots in the face of this pole piece. The cores for these poles are assembled in the same manner Fig. 31. The Pole of a Slow-Speed Engine Type Generator Courtesy of General Electric Company as other field poles but are drilled and tapped for pole bolts. These poles are slightly spiraled on the rotor spider in order to reduce magnetic hum when the machine is carrying load. The field coils are wound with rectangular double cotton covered wire, as this shape increases the copper area of the coil. The usual treatment is given the coil to properly insulate it. These rotors are supplied with or without damper windings depending upon the operating requirements the machine must meet. When these are supplied, they are made from either brass or copper bars embedded in the slots of the pole face, fitted into holes in the end rings and silver soldered under red heat. The silver solder forms a strong low resistance connection and has exceptional penetrating qualities. To facilitate pole removal, the end rings are made in sections. DIESEL ENGINE GENERATORS The Diesel Engine generator is of the slow-speed heavy con- struction type similar to the machine just previously discussed. Due to the more recent development of alternators for this type of drive, 38 TYPES OF ALTERNATING-CURRENT GENERATORS 29 the frame construction is nearly all fabricated, rolled and welded. The speeds of these machines very closely parallel those for the slow- speed engine type ranging from 257 to 450 r.p.m. Somewhat more rigidity must be put into the rotor shaft on account of the tendency GUARD BRUSHES BASE FIELD COIL VAL A.C.LEADS SLIP RINGS በብዝዝዝዝን Fig. 32. A Large Slow-Speed Alternator to be Driven by a Diesel Engine Courtesy of Electric Machinery and Manufacturing Company of Diesel engines producing oscillating torque effects. Heavier damper windings are used on the poles to aid in smoothing out the engine torque when alternators are constructed especially for this prime mover. Fig. 32 shows a fabricated frame alternator built to operate with Diesel engine drive. Note the extremely heavy rotor flange to which the poles are bolted. The ad- ditional flywheel effect secured with this material is an aid to smoother operation of the unit. Even with the heaviest rotors, ad- ditional material is required to keep down the hunting tendencies of Diesel driven alternators. A heavy flywheel is usually provided 39 30 TYPES OF ALTERNATING-CURRENT GENERATORS for this purpose. Fig. 33 shows a modern Diesel direct connected to an alternator with the stabilizing flywheel. Reciprocating steam engine driven generators have this same hunting tendency, but it is more pronounced in the Diesel so that heavier flywheels are re- quired than are ordinarily used with steam units. THTO Fig. 33. A Diesel Engine Plant Consisting of Two Alternators with Direct-Connected Courtesy of Electric Machinery and Manufacturing Company Exciters TURBO-GENERATORS Turbo-generators differ very materially in design and appear- ance from other types of generating equipment. The high speeds at which the rotating element operates requires a small diameter in order to reduce the stresses set up by centrifugal action. Noise and vibration set up by high-speed machines are muffled to some extent by totally enclosing the unit with sound deadening materials. In order to cool the equipment under these conditions, forced ventila- tion is resorted to. With the larger units this circulated air is washed and cooled before being blown through the alternator. 40 TYPES OF ALTERNATING-CURRENT GENERATORS 31 Many smaller units use reduction gears between the turbine ele- ment and the generator shaft. With geared units the generator can be of the standard belt-driven type. With capacities ranging from 10,000 up to 200,000 kilovolt amperes gearing would not be feasible. Fig. 34 shows a belt-driven type alternator connected to the steam turbine with reducing gears. Note the direct-connected exciter unit- mounted on the alternator frame. Units of this particular type shown are made in capacities from 30 to 50 kilowatts. ALTERNATOR. EXCITER D.C.LEADS A.C.LEADS A.C. WINDINGS GOVERNOR HOUSING REDUCTION GEAR CASE STEAM TURBINE Fig. 34. A Medium Size Alternator Driven through Reduction Gears by a Small Courtesy of Westinghouse Electric and Manufacturing Company Steam Turbine The large high-speed direct-connected generators, Fig. 35, re- quire a considerable change in the design from other types, especially in rotor construction. Note the totally enclosed features with ar- rangements for quick removal when cleaning and inspection are necessary. The pedestal-type bearing permits the rotor to be easily and quickly lifted from the stator with overhead crane should re- pairs be necessary on windings or bearings. Stator iron and coil construction are not essentially different from other types of alternating-current generators. The iron is stacked so the slots are longer to accommodate the rotor poles. Coils are considerably longer with the straight sides imbedded in the stator slots wrapped with mica insulation. On account of the greater flexibility required at the ends of the coils these are wrapped with 41 32 TYPES OF ALTERNATING-CURRENT GENERATORS treated cloth tape. Mica wrapped coils have greater dielectric strength, better heat conducting qualities, which improve reliability and efficiency for machines insulated with it. Better anchorage for the armature coils is secured through the use of insulated brackets. Adequate bracing is obtained by lashing the coils to these supports at frequent intervals. Temperature detectors for checking the operating temperatures COVER TO AIR DUCT- END BELL BEARING Fig. 35. A Large High-Speed Horizontal Turbo-Alternator Type of Generator Courtesy of Westinghouse Electric and Manufacturing Company are located in the stator slots at points where the heat is expected to be greatest. The rotor, shown in Fig. 36, is machined from a solid steel forg- ing. The slots for the field coils are machined radially to reduce noise from magnetic effects on the stator laminations. Field wind- ings are made by forming continuous copper strip wound edgewise to form the coils. Metal wedges hold them securely in the slots. Mica strip is used between the conductors for turn insulation while moulded mica is placed between the coils and the pole piece. As the coils are made, each turn is given a treatment of special insulat- ing varnish. The end turns are securely braced and the rotor is finally baked at a high temperature during which time it is subjected to a very high pressure applied through the use of clamping rings. This treatment eliminates air spaces and forces 42 TYPES OF ALTERNATING-CURRENT GENERATORS 33 all excess binding material so the whole coil becomes an almost solid homogeneous mass. Collector rings are made from a tool steel forging. These are then shrunk on a mica bushing which insulates them from a steel bushing pressed on the shaft. All joints and connections to these rings are silver soldered at high temperature to prevent loosening up under normal operation. FIELD GOIL SLOTS END SHIELD FAN ROTOR LAMINATIONS Fig. 36. Rotor of a High-Speed Turbo-Alternator Courtesy of Westinghouse Electric and Manufacturing Company WATER-WHEEL GENERATORS Alternators for use with water-power units are made in both vertical and horizontal types. A far greater percentage of water- wheel driven machines are for vertical drive. The slowest speed machines made are driven by hydro units. The 9000 kilovolt ampere units at Keokuk are only 58 revolutions per minute and the 5000 kilovolt ampere units at Niagara run 250 revolutions per minute. The units for use with low heads of water run slower than higher head machines. Fairly high speeds are used on water-wheel units, 300 to 600 r.p.m. being common in capacities ranging from 10,000 to 20,000 kilovolt amperes. Next to turbine driven units the water-wheel generators are the largest constructed, as capaci- ties as large as 22,000 kilovolt amperes have been built in horizontal type and 45,000 kilovolt amperes in the vertical type. Figure 37 shows one of the large slow-speed water-wheel genera- tors in operation at Muscle Shoals. The stator design of these large machines does not vary greatly from other types of alternating- current generating equipment. In some of the larger machines, the 43 34 TYPES OF ALTERNATING-CURRENT GENERATORS section of the coil in the slot is treated with bakelite and hot pressed. This process makes a more rigid coil which is less subject to damage to the strand insulation while the coils are being assembled in the stator. Due to the wide range of speeds at which various water-wheel EXCITER THRUST BEARING STATOR CORE 800 O WATER WHEEL GOVERNOR Fig. 37. A 25,000 Kv-a. Vertical Water Wheel Type of Generator Courtesy of Westinghouse Electric and Manufacturing Company units operate, no single design of rotor will meet all requirements. For lower peripheral speeds a fabricated steel spider is employed as shown in Fig. 38. The poles are either bolted or dovetailed to the rim, Fig. 39. For the moderately higher speeds laminated steel or steel plate is used. The large relatively high-speed machines have a laminated rim, Fig. 40, to which the pole pieces are dovetailed. The coils for the rotor poles are usually double cotton covered magnet wire for the smaller sizes and strap wound for the larger units, as shown in Fig. 39. Many smaller hydro plants have been made for full automatic operation. Thermal protection is provided in the winding and bear- ings through relays which fully protect the units against overload or oil failure. In case of a shutdown the machines will go through the sequence of starting operations three times. If at this time the 44 TYPES OF ALTERNATING-CURRENT GENERATORS 35 trouble has not cleared, an attendant must visit the plant and clear the difficulty before the machine can be operated. MOTOR GENERATORS Motor generator sets are made in practically all capacities from fractional horsepower units used for supplying radio sets to 7000 POLE SHOE- FAN BLADES WELDING HUB- FIELD COIL- Fig. 38. A Rotor Built up by Welding Steel Plates and Angles. The Poles are Fastened to the Rotor by use of Dovetail Slots Courtesy of Westinghouse Electric and Manufacturing Company kilowatt sets used for large power applications. Some of these are used to convert alternating-current to direct-current while others change direct-current to alternating-current and some direct-current to direct-current where a change in voltage is desired. A line of small motor generator sets has been made for produc- ing alternating-current power to operate radio sets in locations where only direct-current power is available. Some of these were only 100 45 36 TYPES OF ALTERNATING-CURRENT GENERATORS DAMPER WINDINGS SLIP RINGS ROTOR HUB FIELD COILS Fig. 39. A Large Rotor with Damper Windings and Pole Pieces Bolted to Rotor Courtesy of Westinghouse Electric and Manufacturing Company POLE SHOE POLE DOVE TAIL ROTOR WELDING Fig. 40. A Large High-Speed Rotor with Pole Pieces Dovetailed to It Courtesy of Westinghouse Electric and Manufacturing Company 46 TYPES OF ALTERNATING-CURRENT GENERATORS 37 watts for isolated plant use, usually 32 volts direct-current to 110 volts alternating-current. Others for hotel and similar service were one kilowatt units and operated on 115 volts direct-current to 110 alternating-current. All the radio sets in one section of a building would be operated from a single unit. Motor generator sets are rapidly being replaced by converters as they operate more efficiently and cost less to build than do motor generator sets. See Fig. 41. HIGH-FREQUENCY GENERATORS A line of high-frequency generators which will vary the fre- quency from 60 to 240 cycles is made in capacities from 5 to 100 kilowatt. These machines are sometimes referred to as frequency changers. A machine of this type is usually made from a slip 100 Fig. 41. A Motor Generator Set. An Adjustable Speed Direct- Current Motor Is Driving an Alternating-Current Generator Courtesy of Reliance Electric and Engineering Company ring motor preferably driven by a variable speed motor. The stator of the slip ring motor is connected to the line and the motor to be driven to the slip rings. The variable speed motor drives the rotor of the slip ring motor in the opposite direction from which the stator currents would rotate it. This will produce frequencies from the line frequency up to three times line frequency by 50 per cent over speed in the rotor; thus a 4-pole 60-cycle slip ring motor driven at 2700 r.p.m. will produce 180 cycles. A 2-pole motor connected to this frequency changer would have an operating speed of 10,800 r.p.m. Woodworking plants frequently require high-speed motors, and motor generator sets, arranged as described, produce the necessary speeds. 47 38 TYPES OF ALTERNATING-CURRENT GENERATORS Machines have been made for producing very high frequencies, some as high as 500,000 cycles for operating induction coils. At the present time all new high frequency circuits are operated from oscillations set up by vacuum tubes. This method is proving so satisfactory that motor-generator machines are no longer advertised for this purpose. FRAME STATOR WINDING ROTOR WINDING BEARING BRACKET BEARING EXCITER ROTOR FIELD TERMINALS A SYNCHRONOUS INDUCTION MOTOR AND EXCITER ARMATURE, WITH TOP HALF OF BEARING BRACKET AND EXCITER FRAME REMOVED TO SHOW THE DIFFERENT WINDINGS Courtesy of Westinghouse Electric and Manufacturing Company, East Pittsburgh, Pa. 48 TYPES OF ALTERNATING - CURRENT MOTORS Two or more magnetic fields are always required in either direct- or alternating-current motors to produce torque. These fields set up magnetic poles which act upon each other through at- traction or repulsion to produce the rotating forces called torque. The construction of the machines for utilizing direct current are quite different as a rule from those using alternating current to pro- duce these magnetic forces. The stationary field and revolving armature, with most of the line current passing through brushes to the moving element, is al- most universally used with direct-current motors. The alternating- current motor has practically the reverse arrangement, as this machine nearly always has the main line current passing through stationary windings. This current passing through these windings sets up a revolving field which acts on the rotating element in various ways with different types of motors to produce torque. How this is accomplished in the various types of alternating-current motors will be explained in the discussion of each. The important points of dif- ference to bear in mind are these. The direct-current motor has stationary poles and a revolving armature, while the alternating- current motor has stationary coils with rotating field flux. The stationary part of a direct-current motor is called the field and the moving element the armature. The stationary part of the alternating- current motor is called the stator and the moving element of the mo- tor is called the rotor. -- SPEED OF ALTERNATING-CURRENT MOTORS The speed of a direct-current motor can be easily changed by raising or lowering the applied voltage or using resistance in either the armature or the field circuit, wide ranges of speeds being ob- tainable with the direct-current motor through this means. Only very limited speed ranges are possible with alternating-current motors. One of the elements producing torque in the alternating- 49 2 TYPES OF ALTERNATING-CURRENT MOTORS current machine is the revolving field. No rotor of an induction motor can revolve faster than this field rotates. The top speed of a motor on an alternating-current circuit then becomes the synchro- nous speed of this revolving field. More about this fact will be dis- cussed under each type of motor. The speed of this rotating field is determined by the number of poles and the rapidity with which these change from north to south. The frequency which is determined by the number of changes of polarity in the poles depends upon the number of cycles per second obtained from the alternator supplying power to the circuit. A 2-pole motor connected to a 60-cycle source would have 60-pole changes each second for each pole which would make 3600 changes per minute. Therefore, the stator field would rotate at a syn- chronous speed of 3600 and would limit the rotor speed to a like amount. If the stator was wound with four poles instead of two, the rotor would advance only one-half a turn for each cycle of change; hence, two cycles would be required on the stator to turn the rotor one complete revolution. Thus with a 4-pole stator the rotor speed would be 1800 revolutions per minute or one-half what it was with a 2-pole stator. A stator wound with six poles would require three complete cycles or pole changes to make one complete turn of the rotor. Mathematically the synchronous speed of a rotor would be cycles X 60 X 2 r.p.m.=number of poles Sixty is used because there are 60 seconds in a minute and two must be used because it requires a pair of poles, one for each half cycle, to make the magnetic circuit. If the frequency was changed from 60 to 40, the speed at which the poles would change polarity would shift the same amount. A 60-cycle motor on a 40-cycle circuit would run at only two-thirds its former speed. Note-this is not a practical thing to do but is used merely for illustration. A motor under these conditions would run hot because of lack of iron in the magnetic circuit for the lower frequency. It is well to note at this time that the number of phases of the circuit supplying the motor has nothing to do with the speed at which it operates. 50 TYPES OF ALTERNATING-CURRENT MOTORS 3 SINGLE-PHASE MOTORS Single-phase motors may be classified according to the three following groupings: (1) series; (2) induction; and (3) repulsion. Taken as a whole the induction type is much more numerous than the others although certain fields of application may be almost. wholly supplied with one type. The small motor-driven tool and appliance industries use enormous quantities of series type motors with some companies making a specialty of this particular motor. The induction type is used in practically all applications where con- stant speed is desirable, as this motor is like the shunt in this charac- teristic. The repulsion motor provides better starting than the in- duction type and is also widely used where variable speed is required from an alternating-current source of power. Many types of re- pulsion motors have been developed, over half of which are now obsolete. Practically all companies making alternating-current machines make a repulsion motor. Some of these are discussed later in this lesson. Torque. An induction motor may have running torque but has little or no starting torque. Why this condition exists is explained by Fig. 1. A squirrel cage rotor is used in this illustration as it simplifies the diagram, and the theory is exactly the same whether the armature is wire wound or made up from short-circuited bars. Fig. 1 shows a 2-pole stator with single-phase winding connected to lines L1 and L2. During one-half cycle the current is flowing into the stator winding from L1. This makes the top half of the stator a north pole and the lower half a south pole. The flux in the stator, set up by the current during the first half cycle, will cut the rotor bars and induce currents in them as shown in A, Fig. 1. As these bars are short-circuited by end rings, currents will flow in the bars and cause the rotor to be polarized with a north pole, N, at the top and a south pole, S, at the bottom, as in B, Fig. 1. This position of the rotor poles with reference to the stator poles with north pole N at the top and south pole S at the bottom will produce no torque in the rotating member because the rotating forces are equal and in opposite directions. During the next half cycle the polarity conditions of both stator and rotor will be exactly reversed and no starting torque will be produced. 51 4 TYPES OF ALTERNATING-CURRENT MOTORS As long as the rotor and stator poles have this relationship, no torque can be developed, because some angular displacement of the rotor and stator pole positions must take place before any turning action becomes effective. How this displacement of the poles on the stator and rotor is effected for starting will be explained under split-phase motors. The single phase motor differs from the polyphase motor in ROTOR L₁ STATOR L2 L₁ JOVOL L2 Tomor N о S A N O S STATOR FLUX Berendi STATOR FLUX N SO S ROTOR FLUX' B о → ···Ⓡ + ROTOR FLUX C D Fig. 1. Direction of Flux Paths in Stator and Rotor N the following respect. The poles alternate in the single phase machine while the stator flux rotates when more than one phase is used. Figure 1, C and D shows the relative positions of stator and rotor polarities when the rotor is driven at synchronous speed in the changing field of the frame. In the case of a two-pole motor, the rotor would have to be turned once for each cycle. This rotation of the moving member causes the polarity to be at right angles to the stator poles. The main poles are located at the top and bottom while the induced poles are on the right and left sides of the rotor. 52 TYPES OF ALTERNATING-CURRENT MOTORS 5 This is the position which produces the maximum torque. Just why the rotor poles are now at right angles to the main poles is rather difficult to understand. This shift of poles from positions in Fig. 1 to the positions they now occupy is caused by the rotor rotation. Figure 2 shows the stator flux polarity on the second half of the cycle resulting from the current supply furnished by L1 and L2. This figure shows the rotor flux condition at very nearly synchronous speed. The rotative affect has now caused the rotor polarity to shift almost 90 degrees with reference to the stator polarity. A comparison of Fig. 2 with Fig. 1 will clearly indicate this fact. L L2 Fig. 2. S 田 ​N Θ A N, N₂í S2 IS, Direction of Flux when Stator Current Is Flowing from L2 to Li and Rotor Running at Synchronous Speed This relationship of rotor pole position with stator pole position results in maximum available torque. The angle between the true 90 degree position and the actual pole position is caused by the slip. In any motor where the rotor field is produced by the flux of the stator setting up a voltage in the rotor winding, the revolving or changing field must rotate faster than the moving element of the machine. Otherwise, no flux could cut the rotor and no voltage would be produced to force current through the circuits in the armature of the machine. This difference in speed between the revolving field and the rotor is called the slip. This usually varies from two to seven per cent on well-designed squirrel cage machines. It is seldom over four per cent on three-phase motors of this type. Series or Universal Motor. Figure 3 shows the diagram for a series or universal type of single-phase motor. This machine is almost identical with a direct-current series motor. The alternating- current conditions require that these machines have laminated iron pole pieces as well as the laminated armature. This construction 53 6 TYPES OF ALTERNATING-CURRENT MOTORS eliminates eddy currents in frame and pole pieces. In this motor both the stator and the rotor are magnetized from the line current. 11 L2- 1 COMMUTATOR FRAME ARMATURE Fig. 3. A Series on Universal Motor with Current Flowing as Shown by Arrows POLE When the current reverses in one part of the machine, it reverses in the other at the same time. This means that the operation with alternating current is essentially the same as though direct current was operating it. Fig. 4 shows the conditions in the series diagram in Fig. 3 on the second half of the cycle only. The direction of the current is reversed, but the polarity relationship between the arma- ture and the stator are relatively the same so the torque is developed regardless of the current direction through the motor. Thus, it is very essential that the direction of magnetism in the field and armature reverse at the same exact instant, because if one reversed first the direction of the torque would be reversed mo- mentarily. Universal motors will have somewhat different load speed characteristics on direct current than on alternating current. The inductive effects present in the alternating-current circuit will cut down the current and reduce the speed below what it would be on a L, ARMATURE WINDING L₂- FIELD COIL BRUSHES DO DOE Conce 200 Fig. 4. The Direction of Current Flow One-Half Cycle Later Than in Fig. 3 direct-current circuit of the same voltage. Motors of this type are used principally on small appliances such as drills, scrubbers, blowers, 54 TYPES OF ALTERNATING-CURRENT MOTORS 7 vacuum cleaners, sewing machines, mixers, etc. To meet these types of service, capacities from 1/150 to 1 horsepower have been de- veloped. Universal motors have high starting torque and operate most efficiently at speeds of 4000 to 10,000 revolutions per minute, speeds possible only with small armatures. Fig. 5 shows the parts of a universal motor just described. Many applications where universal motors have been tried show BRUSH SHUNT INSULATION dro SPRING BRUSH THOLDER BRUSH SLOTS SHAFT ARMATURE WINDING CORE COIL LEADS TWINE BAND STATOR WINDING 11 COMMUTATOR Fig. 5. Parts of a Westinghouse Type AD Universal Motor unsatisfactory results on account of the wide difference of the speed behavior of the motor when operating on direct and alternating current. To meet this condition, many concerns make two motors, one of alternating-current and the other for direct-current use. These are interchangeable so far as dimensions are concerned. This development indicates that considerable judgment must be used in universal motor application. Larger capacity universal motors require an additional wind- ing on the stator to cut down the high inductive effects at the brushes. This winding, called a compensating winding, is wound so that its field will neutralize the field of the coils being commutated, thus helping to reduce abnormal sparking. This would make the com- pensating winding 90 degrees from the main or stator windings. It 55 8 TYPES OF ALTERNATING-CURRENT MOTORS is connected in series with the main winding and armature. The high resistance of the small motor coils takes care of the inductive effects on small machines, but the low coil resistance and higher voltage usually used aggravate sparking at the brushes on larger motors of this type requiring a neutralizing winding to enable the machine to operate satisfactorily. Series motors used on alternating current have considerable advantage over direct-current series motors. Through the use of a transformer with a number of taps on the secondary, the voltage at the motor terminals may be efficiently changed. This variation of the motor terminal voltage provides a wide range of speeds obtain- able with the alternating-current motor. A large universal motor has been successfully developed for railway work. The direct-current voltage of 550 volts is used from the trolley on city streets and 1300 volts can be used from a trans- former when the car runs in interurban territory. This motor gives very satisfactory operating characteristics on either system and is widely used for this type of work. Split-Phase Motor. The split-phase motor is a squirrel cage motor with two windings on the stator, one of which is the running winding and the other the starting winding. A glance at Fig. 1 shows the conditions in the stator and rotor magnetic circuits with the like poles on each, exactly opposite, producing no starting torque. One of the most common methods of obtaining a displaced polarity condition between the rotor and the stator fields, to bring about torque for starting purposes, is to add another set of coils to the stator as shown in Fig. 1. These coils are wound 90 degrees from the original set and are connected to the power circuit only during the period of starting. The leads to this switch are disconnected from the line by a centrif- ugal switch as soon as the motor reaches about 85 per cent of syn- chronous speed, and remain off the line until the speed drops to approximately 60 per cent of normal when they will be cut in on the line again by the switch. Unless the speed comes up to normal in a short time after the reduced speed, this winding may burn out. The running winding R shown in Fig. 6 is the same winding as shown in Fig. 1. The starting winding X is wound between the coils of the running winding R and has high resistance and low induc- 56 TYPES OF ALTERNATING-CURRENT MOTORS 9 tance while R has a low resistance and high inductance. This will give the two windings a phase displacement of the two currents flow- ing in the running and starting coils approximating the conditions in a two-phase circuit. Instead of the polarity of the stator winding shifting 180 degrees and changing the polarity of the main wind- ing to a like amount, this additional set of coils causes a shifting of the magnetic flux only 90 degrees for a half cycle change in current. In Fig. 7, consider R the running winding to be phase 1 and the starting winding X to be phase 2. The current in R is at a maxi- mum value positively while the current in X is just ready to start L₁ RUNNING WINDING L₂ R. DEEL 15 Yooy YN X STARTING WINDING STATOR R ROTOR Fig. 6. Diagram of a Single-Phase Motor with Starting and Running Windings positively. As the current in R gets smaller, weakening its magnetic effect, the current in X is getting larger, strengthening its magnetic effect. The result is a polarity which moves around the rotor in a clockwise rotation. This in effect is a rotating magnetic field around the rotor which cuts the rotor bars setting up local circuits in this element, polariz-. ing it. These magnetic poles set up in the rotor tend to follow the main poles and a starting torque is produced. While this torque is weak compared to the running torque developed, as the rotor ap- proaches synchronous speed, it is sufficient to start light loads found in many types of motor applications where fractional horsepower motors are used. Split-phase motors are made only in fractional horsepower sizes for use where small amounts of power are needed from a single-phase lighting circuit. The starting torque is too low to start only very light loads, and the starting current is high, which causes line voltage disturbances. In some applications, a clutch disconnects the motor 57 10 TYPES OF ALTERNATING-CURRENT MOTORS from the load until it is up to speed where it has normal torque. Condenser in One Leg. Some split-phase motors are wound with two sets of coils like a two-phase motor as shown in Fig. 7. As the currents in coils R and X normally would be in phase from a single-phase source, resistance and capacity are introduced in coil X. This causes the current in coil X to lead the voltage which would result in a phase angle between the currents in the two coils. The resulting magnetic poles moving around the stator would develop starting torque, and the motor would operate very similar to a two- phase machine. This type of starting for split-phase motors is more expensive than starting winding with the switch, but it improves Լ, RUNNING WINDING L2- CONDENSER, R+ oo IN X STARTING WINDING R LE RESISTANCE Fig. 7. Method of Connecting a Condenser and Resistance in a Split-Phase Motor power factor, efficiency, and slip, as this motor acts more like a polyphase induction motor. In order to increase the effectiveness of the condenser for start- ing, in some cases an auto transformer is used to raise the voltage across the condenser terminals to three or four times normal. The condenser is sometimes left in the circuit with line voltage across the terminals while the motor is operating, as this improves efficiency and power factor of the motor. Figure 8 shows a capacitor-start induction-run motor for use in refrigerators, stokers, oil burners, and other household appliances where higher starting torque is required than is obtainable with the split-phase motor. There is also less radio disturbance from this motor than is caused by the split-phase machine. Reactance in One Leg. Reactance may be used in one leg of a two-phase winding for starting on single phase. This consists of a choke coil connected in one phase of the winding on the stator. 58 TYPES OF ALTERNATING-CURRENT MOTORS 11 This lagging of the current in one phase caused by the choke makes displaced phase relations between the currents in the two coils on the stator windings which sets up the starting torque in the rotor. In some cases a choke is used in one leg as a current limiting device when the condenser is utilized for starting. This tends to limit line disturbance but cuts down the starting torque of the motor. Fig. 8. Wagner Single-Phase Induction Motor with Electro- lytic Condenser Mounted on Top Resistance Wire. The use of resistance wire in the winding of the stator has been used in a few small motors to obtain this split- phase condition for starting. A few coils of resistance wire have been interspersed in the main winding to produce starting torque. Motors of this type have usually been fan motors in which efficiency is a minor item in the operation. Better methods have been de- veloped which have made this type of construction nearly obsolete. High resistance leads, from the coils to the commutator segments, are sometimes used with single-phase straight series motors to re- duce sparking which is especially bad during the starting period. 59 12 TYPES OF ALTERNATING-CURRENT MOTORS Squirrel Cage Rotor. Practically all motors of the split-phase type, now being manufactured, use the squirrel cage rotor and the wound stator, as this method of construction has proved much superior to the reversed scheme of the squirrel cage stator and the wound rotor. Fig. 9 shows clearly the main windings, the starting THRUST WASHER INSULATED DISC SPRING GOVERNOR LINKS STARTING LEADS FIBER- STARTING CONTACT CONTACT SPRINGS STARTING WINDINGS MAIN WINDINGS 0 000 FAN OIL SLINGER SQUIRREL CAGE WINDING TERMINAL BOX GOVERNOR WEIGHTS -BASE Fig. 9. (Top) Rotor of Century Split-Phase Motor Showing Governor Which Opens Starting Windings (Bottom) Rotor Assembled in Stator Showing Arrangement of Open-Circuiting Device Courtesy of Century Electric Company windings, and the open circuiting switch operated by the rotor of a motor of the split-phase type. Split-phase motors with the squirrel cage stator and the running and starting coils on the rotating member were made quite extensively by the General Electric Company up until a very few years ago. Due to the fact that the coils could be machine wound, the cost of construction for this type of motor was very low and therefore large 60 TYPES OF ALTERNATING-CURRENT MOTORS 13 quantities of these motors were sold. The construction shown, Fig. 10, required the power supplied to this machine to be passed through the carbon brushes to the bronze rings as shown on the rotor. Trouble was experienced from brush and ring wear with the resultant spark- ing causing considerable radio interference. There are two classifications of alternating-current commutator motors-those in which the speed materially changes with the load are called series motors, and the others in which there is only a slight change in speed with load are termed shunt motors. The latter type 0 Co C+ 23 6 22 23 26 0 市 ​10 Fig. 10. General Electric Type SA Single-Phase Rotor may be connected with auxiliary equipment which provides a vari- able voltage through which the speed may be increased or decreased independently of the load. They are still classified as alternating- current shunt motors however. Many of the repulsion type motors discussed later in this lesson fall in the latter classification. Repulsion Motor. The repulsion motor has the stator coil connected to the line. The armature is wound like a direct-current machine but has no connection to the line. Short-circuiting brushes provide an armature circuit which has an electromotive force across it because of the magnetic effects of the stator winding. The poles set up by the induced current in the rotor are the same polarity as the stator poles. The torque is set up by the opposing forces between these sets of like poles from which comes the name repulsion motor. A series motor, with the stator winding connected to the source of supply and the armature short-circuited, would become a motor of 61 Um 14 TYPES OF ALTERNATING-CURRENT MOTORS this type. The repulsion motor finds a wide field of application where comparatively high starting torque is essential. A great many modifications have been made of the original repulsion motor de- veloped by Elihu Thompson as early as 1887. Fig. 11 shows a diagrammatical representation of this early motor. The armature is provided with a pair of brushes for each pair of poles on the stator L FIELD WINDING www ROTOR L2 Fig. 11. Diagram of Circuits in the Early Repulsion-Induc- tion Motor winding. All positive brushes are short-circuited with all negative brushes. BRUSHES SHORT-CIRCUITED Currents developed in the rotor, through the action of the stator flux, will develop torque in any position of the brushes between poles except at the halfway point. Here as much rotative effort will be developed in one direction as the other; therefore, the result will be zero and no torque will result. This is made clear from an inspec- CURRENT ARMATURE SHORT CIRCUITED. 01010 BRUSHES TORQUE A 3 A 2) COMMUTATOR Fig. 12. Diagram Showing the Direction of Induced Voltage, Current, and Torque in a Repulsion Motor tion of Fig. 12. This shows stator coil A setting up a magnetic field across the rotor which changes polarity with the frequency of the supply circuit. This induces an electromotive force in the rotor windings. With brushes as in position (1) the electromotive force developed in the right side of the rotor will be exactly equal and opposite to electromotive force in the left side of the rotor. With 62 TYPES OF ALTERNATING-CURRENT MOTORS 15 brushes set at the position where these electromotive forces meet, a large current will flow, but no torque will be developed because the turning effort on the two sides of the rotor balance each other. If the brushes are now moved into position (2), we have a condition of balanced voltages across the brushes as shown by the two sets of arrows and no current flows through the short circuit. With brushes L₁ L2 STATOR WINDING www W Fig. 13. Diagram of Circuits of an Atkinson Repulsion Motor SHORT-CIRCUITED ARMATURE L2 in position (3), the condition of unbalanced voltage would cause current to flow through the short circuit and the turning effort would be more in one direction than the other, so useful torque would result causing the rotor to turn. COMPENSATING WINDING ATKINSON MOTORS The Thompson or original repulsion motor worked satisfactorily as long as lower voltages and small sizes were made. When larger sizes were made and higher voltages were applied to these motors, EXCITING - CURRENT BRUSHES SHORT-CIRCUITING BRUSHES COMPENSATING WINDING Fig. 14. Diagram of Circuits of Latour-Winter-Eichberg Repulsion Motor a great deal of commutator trouble developed from the large induc- tive effects on the short-circuited coils. The compensating winding was found to be a satisfactory solution for this trouble in the alternating-current series motor, so Atkinson applied the idea to the Thompson motor. The result is the conductively compensated re- pulsion motor shown in Fig. 13. Another variation of the com- pensated single-phase repulsion motor is shown in Fig. 14. This 63 16 TYPES OF ALTERNATING-CURRENT MOTORS motor employs two sets of brushes, one to pass the line current through the armature like a series motor and the other to short- circuit the armature to produce the repulsion effect. This idea is jointly credited to men by the names of Latour, Winter, and Eich- berg. The advantage of the last arrangement is in the elimination of the stator coil; the armature winding is made to furnish this field more effectively than was the case with a stator winding. All of the repulsion motors discussed have the direct-current series motor characteristic of losing considerable speed as the load is applied. REPULSION-START INDUCTION-RUN MOTORS The repulsion-start induction-run motor is by far the most numerous of all the various types of single-phase motors. This machine has the operating characteristics of the induction motor with starting torque from two to five times full load running torque. For the same line current it has higher starting torque than any other type of single-phase motor. Its maximum torque varies from. 2 to 2¼2 times full load torque and its pull in torque from 1½ to 2¼ times its full load value. The stator is usually wound with two sets of coils which makes possible the use of the motor on either 110 or 220 volts by simply connecting the coils in parallel or series. The stator core is high- grade steel laminations riveted together under pressure. The cores of these machines are usually insulated and completely wound be- fore being inserted into the frame. This type of construction makes repairs simply and quickly made, as a spare core may be kept on hand to replace burn outs. Frames are usually rolled from steel sheets, as this provides greater rigidity with less weight than is possible with cast frames. The feet are welded to the frame. Various types of vibration ab- sorbing bases are available for special applications where noise is objectionable. Some of these use steel spring mountings and others are set in rubber. The armature for repulsion-start induction-run motors is made of laminated iron and wound with coils like a direct-current or re- pulsion type machine. The commutator is provided with a short- 1 64 TYPES OF ALTERNATING-CURRENT MOTORS 17 STATOR WINDING WINDINGS IN ROTOR SLOT ROTOR WINDING GOVERNOR WEIGHTS BEARING SHAFT WOOL YARN OIL WELL OIL CUP GOVERNOR RODS BEARING BRACKET SLOT IN STATOR STATOR CORE INSULATION STATOR WINDING -BASE MICA MICA COMMUTATOR -RING FACE OF COMMUTATOR BRUSH HOLDER SPRINGS BRUSH LIFTING DEVICE -BRUSH HOLDER CARBON BRUSH SPRING BARREL SHORT CIRCUITING SEGMENTS -LEADS FROM ROTOR COILS TO COMMUTATOR BARS STATOR WINDINGS FRAME Fig. 15. Cutaway Section of Century Repulsion-Start Induction Motor 65 18 TYPES OF ALTERNATING-CURRENT MOTORS circuiting device which short-circuits the coils and makes the ma- chine function like a squirrel cage induction motor once it is up to speed. The short-circuiting device is operated by a centrifugal switch which forces a copper ring, made of small segments, against the commutator bars after the proper speed is reached. This is usually about 80 per cent of synchronous speed but varies with different motor manufacturers. End type and ring type commutators are both used with repulsion-start induction-run motors. Some are made to throw the COMMUTATOR- BRUSH HOLDER RING SPRING BRUSH HOLDER LINE LEADS KEY Fig. 16. Westinghouse Type CR Induction Repulsion-Start Mor brushes clear of the commutator, while others ride the commutator continuously. No matter what commutator type or brush riding arrangement is used, all of them short the commutator to make the rotor function as an induction machine while operating. During the starting period, the line current either passes through the armature as in Fig. 13 or excites the armature through induction as in Fig. 12, producing like poles on both rotor and stator. The re- pulsion effect sets up the high starting torque characteristic of these motors. Figure 15 shows cutaway section of a repulsion-start induction- run motor built in sizes of 1% to 40 horsepower. This machine has the end commutator with brush lifting rigging used in a very large percentage of these motors. Fig. 16 shows a motor with the ring type commutator on which the brushes ride permanently but carry 66 TYPES OF ALTERNATING-CURRENT MOTORS 19 current only during the starting period. These machines are built in capacities from 34 to 3 horsepower. Some of these motors are built with an inner squirrel cage winding which improves the torque curves of the straight repulsion- start motor. The outer winding connected to the commutator pro- vides the initial starting torque and assists the inner squirrel cage winding by carrying its share of the rotor current while running. This construction provides a motor with very smooth-speed-torque curve with sufficient torque to bring up to speed any load it can start. The speed is nearly uniform from no load to full load. Repulsion-start induction-run motors are used for a great variety of purposes, a few of which are given as illustrations: com- pressors; pumps; farm machinery; ventilating fans; blowers; ma- chine tools; grease guns; car washers; lifts; oil burners; and re- frigerators. Wherever there is a difficult power job to be done and only a single-phase source available, this type of motor will nearly always be found taking care of it. GENERAL ELECTRIC REPULSION-INDUCTION MOTORS The General Electric Company make single-phase repulsion- induction motors with two types of compensating windings. One type has an independent compensating circuit, while the other takes a tap from the main stator winding to neutralize induction. Both of the motors are a modification of the original Thompson motor. The compensating circuits used in this motor improve not only the power factor but also the speed characteristics of the original motor, both of which were very poor. This motor is not a constant-speed machine but is designed to approximate the speed characteristics of a compound direct-current motor. The starting torque varies from 2 to 212 times full load torque. It may be connected directly across the line, but a resistance type starting box may be used if direct starting causes too much line disturbance. The brushes ride the commutator at all times, and the motor may be reversed if the brushes are rotated far enough in any one direction. This motor is built for reversing by using a switch and add- ing another winding to the stator at 90 degrees to the original one. Whichever direction the current flows through this winding, with reference to the original stator winding, will determine the direction 67 20 TYPES OF ALTERNATING-CURRENT MOTORS of rotation of the motor. There are two ways of obtaining adjustable speed for these repulsion-induction motors. The brushes may be shifted, or through the use of a transformer with taps which changes the terminal voltage. For some applications, both the transformer with taps and a brush shifting device are employed to obtain adjust- able varying speeds. Fig. 17 shows a motor of this type for operation on either 110 or 220 volts with a speed variation of 21/2 to 1. It is Fig. 17. Single-Phase Motor in Which Speed Adjustment Is Obtained by Shifting Position of Brushes Courtesy of General Electric Company either reversible or not reversible as required in sizes varying from 1/4 to 2 horsepower. The starting torque will vary with the brush position and will be from 12 to 3 times full load torque for 4-pole motors and from 114 to 21/2 on 6-pole motors. The maximum torque obtainable from this type of motor will be approximately 32 times full load torque. Because this is a constant torque motor, the horsepower output will be proportional to the speed. The no load speed of this motor is about 1.6 times synchronous speed. Unless the motor is properly loaded the speed variation will not be obtained as the series char- acteristics will over speed it. Its principal fields of application are in the operation of printing press machinery and testing equipment. A larger motor for use on polyphase distribution systems is shown in Fig. 18. It can be obtained regularly in 3 to 1 speed ranges but is also available in other speed ratios. These motors have shunt 68 TYPES OF ALTERNATING-CURRENT MOTORS 21 field characteristics which open a wide field of application requiring any number of speed variations. A few examples of the various lines which are powered by these motors are as follows: baking ma- chinery; boiler-house fans; cement kilns; centrifugal compressors and pumps; conveyors; laundry ironers; oil refinery equipment; paper winders; stokers; textile machinery; and rubber working plants. CENTURY REPULSION-INDUCTION MOTORS The Century is not a repulsion-induction motor in the same sense that the General Electric motor is a repulsion-induction type. Fig. 18. General Electric Type BTA 3-Phase Adjustable Speed Motor with a Small Pilot Motor for Shifting the Brushes The Century repulsion-induction machine is, strictly speaking, a repulsion-start induction-run motor as described earlier in this les- son. Fig. 19 shows a detailed cross-sectional view of this motor built in sizes from 1% to 40 horsepower for single-phase operation at 110- or 220-volt. The starting torque of this motor ranges from 212 to 312 times full load torque and will not exceed 32 times full load current when directly connected to the line. The brushes ride the commutator only during the starting period, thus insuring long brush life and noiseless operation. As there is no sparking during opera- tion, this motor causes radio interference only while starting. Its torque characteristics make it especially adaptable to operation of apparatus such as plunger pumps, compressors, oil burners, and re- frigerating machines. 69 22 TYPES OF ALTERNATING-CURRENT MOTORS 2*406NÃO! 8. 6. 7. 8. 9. 10 11. 12. 13. 14. 16. 16. 17. 57 18 19. 20 21. 22- 23 24 25 26 15 14. 27 **W** 6. Field Fibres. 7. Field Core. 8. Rotor Core. 9. Back Bearing Bracket. 10. Rotor Ventilating Grid. 11. Rotor Fibres. 12. Back Flange. 13. Governor Weights. 14. Governor Weight Stud Washers. 15. Governor Weight Studs. | ACELI 3. Fig. 19. Assembly View of a Century Repulsion-Start Induction-Run Motor 1. Eye Bolt. 2. Motor Frame. 19. Oil Ring Guards. 20. Back Bearing. 21. Oil Rings. 22. Bell Crank. 3. Field Ring Locking Screws. 4. Field Ring. 23. Governor Weight Link. 5. Bearing Bracket Cap Screws. 24. Governor Weight Link Rivet. 25. Oil Plugs. 26. Bell Crank Stud. 27. Back Flange Nut. 28. Front Flange. 29. Commutator Head. 30. Commutator Segments. 31. Commutator V. Ring. 32. Parallel Motion Fin- 16. Governor Weight Rivet. 17. Oil Well Covers. 18. Dog Point Bearing Screws. ------- gers. 33. Brush Holder Gib. 34. Gib Screw Lock Nut. 35. Short Circuiting Seg- ments. 36. Gib Screw. 37. Carbon Brushes. 38. Brush Springs. 39. Paper Commutator In- -55 29 30 31 32 33 34 35 36 37 38 39 40 46. Spring Bearing Nut Locking Screw or Spring. 41 42 43 17 .18 19 -47 56 44 46 45 48 49 21 35 38 50 37 25 32 1588=0.88 30 52 -53 -54 sulating Ring. 40. Mica Commutator In- sulating Ring. 41. Spring Barrel. 42. Brush Holder. 43. Spring Barrel Nut. 44. Rotor Shaft. 45. Front Bearing Brac- ket. 47. Front Bearing. 48. Governor Weight Pins. 49. Governor Spring. 50. Paper Commutator In- sulating Ring (Taper). 51. Governor Weight Pin Guide Washer, 52. Parallel Motion Links. 53. Field Ventilating Grid. 54. Subbase. 55. Spring Barrel Ring (Steel). WAGNER REPULSION-INDUCTION MOTORS The Wagner Electric Company makes a line of motors very closely paralleling the Century line. Their repulsion-start induction- run motors are made in sizes from 10 to 15 horsepower in all standard voltages and frequencies. The frame is of rolled steel and welded construction into which the wound stator core is inserted. The stator iron is high-grade annealed sheet made especially for the 70 TYPES OF ALTERNATING-CURRENT MOTORS 23 work. Fig. 20 shows a section of the Wagner repulsion-start induction-run motor stator. Note the excellent coil fit in the slots and the maple wedges holding the coils firmly in place. These Fig. 20. Arrangement of Winding the Pole Groups in the Stator Courtesy of Wagner Electric Corporation stators are thoroughly impregnated with insulating compound and baked twice, after which they are thoroughly sprayed with air-dry varnish to increase resistance to oil and moisture. Fig. 21. Rotor of a Wagner Type RA, Repulsion-Start Induction-Run Motor The rotor shown in Fig. 21 is treated and insulated in the same way as the stator. The slots are slightly skewed to reduce magnetic noise and to eliminate variation in starting torque at different rotor positions. The commutator is of the end type construction and is 71 24 TYPES OF ALTERNATING-CURRENT MOTORS short-circuited by a necklace of small copper segments forced against the commutator by a centrifugal switch. At the same instant this switch short-circuits the commutator, it lifts the brushes so that no contact is made while the motor is operating at normal speed. Wagner also makes a straight repulsion-induction motor in capacities of 1 to 3 horsepower. The rotor, in addition to the wire winding like other armatures for repulsion motors, has a regular Fig. 22. Wagner Type RG Single-Phase Induction Motor www squirrel cage winding. Some of the advantages claimed for this con- struction of winding are: a smooth speed torque curve, without fluctuations, which makes the motor adaptable for severe starting duty; low starting current; close speed regulation; positive opera- tion on low voltage; excellent efficiency; high power factor; excellent commutation with resulting long brush and commutator life; and no internal short-circuiting mechanism. The brushes must be in contact with the commutator at all times. Fig. 22 shows an assembled view of this late development in repulsion-induction motors. 72 TYPES OF ALTERNATING-CURRENT MOTORS 25 DELCO REPULSION-INDUCTION MOTORS The Delco repulsion-induction motor is fundamentally the same as the Wagner and Century motors of this type. These motors have ROTOR GOVERNOR WEIGHT WOOL YARN OIL WELL STATIONARY RINGS Fig. 23. A Capacitor Motor with Internal Condenser. The Starting Winding Is Connected to the Stationary Rings and as the Rotor Approaches Full Speed, the Governor Weight Moves Outward and Opens the Circuit Courtesy of Howell Electric Motors Company CAPACITOR- OIL PIPE LEADS CONDENSER SPRING MOUNTING Fig. 24. Westinghouse Type FT Single-Phase Capacitor Motor. The Capacitor Unit Can Be Removed from the Motor and Mounted at any Convenient Location the end type commutator on the rotor. The short-circuiting device throws against the outside of the commutator while running, which is somewhat different than other motors of this kind. These machines 73 26 TYPES OF ALTERNATING-CURRENT MOTORS are made in capacities from % to 12 horsepower and used principally for refrigeration purposes. The following frequencies are available: 25, 30, 40, 42, 50 and 60 with voltages ranging as follows: 80-160, 100-200, 104-208, 105-210, 110-220, 120-240, 125-250, 150-300, 190- 380, 220-440. Capacitor Motor. The capacitor motor was first developed to provide a quiet operating fractional horsepower machine for driv- ing oil burners, pumps, compressors, stokers, refrigerators, and similar equipment requiring high starting torque, long annual run, and high power factor and efficiency. Motors of this type are made with condensers mounted internally and externally. The external mount- ing is favored especially with smaller units. Capacitor motors are now available up to 10 horsepower, but the condenser unit increases. the first cost very materially over repulsion-induction or squirrel cage machines. Figs. 23 and 24 show how condensers are mounted internally and externally with reference to the motor frame. CLASSIFICATION OF FRACTIONAL HORSEPOWER MOTORS The National Electric Manufacturers Association has set up the following classification of small motors according to what is called the annual service characteristics of the motors. The two classifica- tions are long annual service and short annual service. The short annual period is less than 1000 hours per year, and the long annual period is considerably over 1000 hours per year. Motors with long annual service characteristics are intended for use in general pur- pose applications where the motor is expected to operate at frequent intervals and for long periods of time; where high efficiency and high power factor are desirable; where quiet operation is required; and where normal torque characteristics are needed. Oil burners and refrigerators for household use are very excellent cases. Motors with short annual characteristics are intended for those applications where the motor is expected to operate only at infrequent intervals and for short periods of time. Washing machines and ironers are typical examples of this type of service. POLYPHASE MOTORS How the torque is developed for a two-phase motor has already been shown in the explanation of the operation of a single-phase 74 TYPES OF ALTERNATING-CURRENT MOTORS 27 motor. The only difference between a two-phase winding and a split-phase winding is that the two-phase winding is energized from separate phases of a two-phase circuit while the split-phase is ar- ranged through inductance or capacity to accomplish the necessary current displacement in the two windings. The currents must be out of phase with each other in the two circuits in order to set up torque through the revolving stator field. The two-phase alternator wind- ings are arranged to do this while the single-phase circuit must re- sort to artificial means to meet the requirements necessary to set up a revolving stator field. The two-phase circuit is far superior to the single-phase for providing starting torque for motors. The three- phase revolving field provided from the three-phase circuit has many advantages over the two-phase system. Installation costs are less; motors have better starting characteristics; power factor and speed regulation is better; and efficiency is higher with the three-phase system. Where the single-phase motor has one revolving magnetic field. set up by the stator, the two-phase circuit provides two fields 90 degrees apart, and the three-phase has three fields each 120 degrees apart. This phase relationship is maintained in the motor stator as well as in the generator windings which makes possible the effec- tive use of the magnetic poles provided by these currents. In a non- inductive circuit, the current curves would have exactly the same phase relationship as the voltage curves, but of course with different values. The introduction of a motor in the three-phase circuit would have practically the same phase displacement effect on the current and voltage in each phase, hence the 120 degree-phase relationship of the currents in each phase would be maintained even though the power factor was poor. How the three-phase winding, with its rotating magnetic field, polarizes the stator through the induced cur- rents is shown in Fig. 25. The stator winding is placed around the stator with the various. phases 60 degrees apart. Reversing the connections to one group of coils sets up the 120 degree-phase relationship which always exists. in the three-phase circuit. The current curves for the separate phases are shown in the lower part of Fig. 25. Coils of the stator windings are indicated as A, B, and C. At the first position selected on the sine waves, note that the current in phase A is at a maximum 75 28 TYPES OF ALTERNATING-CURRENT MOTORS value positively, and the currents in phases B and C are both nega- tive, but the current in phase B is approaching zero while the current in phase C is increasing in the negative direction. The induction from these phases causes poles on the rotor indicated by the arrows. Note that the arrows in rotor No. 1 are opposite phase A for the first A 1000 S A C S 0000 2 (3 N N ၂၀၀၀ N C 1000! Looo! PHASE A PHASE B D Tood A 3 4 S 500 ooo 1000 boo PHASE C A N ooo 2 Fig. 25. Rotor Positions During Different Parts of One Cycle B G position on the sine curves. Note how these arrows rotate for each of the four instantaneous valves of current as shown by the four rotor positions. The instantaneous valves of current are taken just 60 degrees apart, which makes the 1st and 4th positions 180 degrees apart. This is a 2-pole winding and the rotor has made just one-half turn from position 1 to position 4. If this stator had been wound with four poles instead of two, the same change on the sine wave would have rotated the rotor only one-fourth of a turn, and a 6-pole one- sixth of a revolution, etc. For this reason rotors used in the stator fields with a large number of poles have slow speeds. Squirrel Cage Motor. The squirrel cage motor is the most common type of alternating-current motor. It is used in single- phase induction motors, two-phase, and three-phase machines. Properly constructed, it is the least troublesome of any moving ele- ment made for motors. The simplest and most common type of 76 TYPES OF ALTERNATING-CURRENT MOTORS 29 squirrel cage is made by assembling a series of copper rods in the slots of the iron rotor case and welding the ends to a copper ring. If viewed with only the copper assembly, it looks like the old- fashioned squirrel cage from which it got its name. The single- phase motor has been already discussed in this lesson, and the two-phase is becoming scarce; therefore, only the three-phase motor will be illustrated and referred to in the remainder of this work. Fig. 26 shows two standard types of rotors. A shows an assembled welded copper bar and B shows the cast aluminum type. RINGS COPPER BARS WELDING Fig 264. Squirrel Cage Rotor as It Would Appear When Removed from the Slots of the Laminated Sheet Steel Rotor Core and Reassembled Fig. 26B. Section of Finished Cast- Aluminum Rotor. The Molten Aluminum Is Cast in Slots in the Laminated Sheet Steel Core Courtesy of General Electric Company The squirrel cage polyphase induction motor is built in any size needed from 1% to 5000 horsepower. Voltages are standardized at 110-220-440-550 and 2200 volts and built for frequencies of 25-, 40-, and 60-cycles. Sleeve bearings, ball bearings, and roller bearings may be obtained if desired, although the roller bearings are not standard with all makes of motors. All types of frames, open, semi- enclosed, enclosed, drip-proof, splash-proof, and explosion-proof, are available wherever the application requires. All manufacturers make motors with 40° C. rating and some add a line of 50° C. motors. A 40° C. motor has a 20 per cent greater overload capacity than a 50° C. motor. A great deal of care is taken in the design of all motors to provide proper ventilation for cooling not only the wind- ings but the iron as well. A current of air directed over and through the machine is usually the method employed to dissipate heat losses. Sometimes additional circulating apparatus is used, but ordinarily 77 30 TYPES OF ALTERNATING-CURRENT MOTORS fans on the motor are used for this purpose. Fig. 27 shows a cross- sectional view of a motor with arrows indicating the direction of air used for ventilation. Up until a few years ago, a squirrel cage motor was the only motor in the constant speed alternating-current field. At the present time all alternating-current motor manufacturers are making at least three and some as many as seven types of squirrel cage induc- tion motors. The three more common types of squirrel cage motors are grouped as follows: First, the normal torque normal-starting-current Cast Fan Guard AIR IN AIR IN TU Solid Cast Frame Dust and moisture proof overlapping machined fit AIR OUT Solid Cast Brackets AIR OUT ·Dust and grease tight cartridge type bearing housing Double width inner race ball bearing Fig. 27. Cross Section of a Fan-Cooled Fully Enclosed Squirrel Cage Motor motor. This motor has the highest efficiencies and power factors of all standard lines of induction motors and is more widely used than any of the others. Some type of starting device is usually required to reduce line disturbance when starting. The second group includes the normal torque, a low-starting-current motor designed to do the work of the ordinary motor but start with less starting current. Smaller and more compact control may be employed with this motor. The third group of motors of this type is high-torque, low-starting- current. These motors have a higher percentage of starting torque than either of the other groups, with a starting current no greater than the second group uses. This motor has high full speed efficiency and power factor and is recommended for driving compressors, con- veyors, and other loads requiring high starting torque. Fig. 28 shows the rotor construction which will provide the third group of motors with desired operating characteristics. Note the double squirrel cage and large deep slots provided for the low resistance part of cage. 78 TYPES OF ALTERNATING-CURRENT MOTORS 31 In Fig. 29 the comparative table gives a picture of the con- ditions developed in various types of squirrel cage rotors by chang- ing the shape of the slots and the winding used. The starting torque, starting current, slip, power factor, and efficiency are the essential factors in analyzing the behavior of a motor. Knowing the motor characteristics is only part of a job of selecting the proper machine to apply to the work. All the operating conditions such as 77 1.1 GALLO Fig. 28. Double Squirrel Cage Rotor Wind- ings. A-High-Resistance, Low-Reactance Winding Which Give High Starting Torque with Low Starting Current. B-Low Resist- ance Winding to Improve Efficiency and Speed Regulations at Full Load Courtesy of General Electric Company. starting, running, power company requirements, voltage, hazards such as explosive dust, flying particles, water and explosive gases must be given consideration before definite decision is made in picking a motor for a job. The interior view of a squirrel cage induction motor, Fig. 30, gives a very clear picture of the construction, assembly, ventilation, and lubrication features of this type of machine. The frame is welded steel, and stator and rotor cores are made from special lam- inated steel. The coils are well protected, and the shaft is pro- vided with a circulating fan which directs a current of air over the windings and the rotor and stator steel. All parts are interchange- able for a given size and can be easily and quickly changed whenever necessary. There is nothing to get out of order except possibly bear- ings and insulation which with proper care rarely happens. Wound Rotor Induction Motor. The squirrel cage induction 79 32 TYPES OF ALTERNATING-CURRENT MOTORS motor provides very little change in speed; only a very limited varia- tion may be made by raising or lowering the terminal voltage. In ROTOR AND SLOT CONSTRUCTION TIX T பி AMARA LEAKAGE FLUX LOW USEFUL FLUX HIGH LEAKAGE FLUX HIGH USEFUL FLUX MEDIUM HIGH RESISTANCE WINDING WAZA WORD CHAR. LEAKAGE FLUX HIGH LOW RESISTANCE WINDING USEFUL FLUX MEDIUM LEAKAGE FLUX HIGH ·USEFUL FLUX MEDIUM LEAKAGE FLUX LOW USEFUL FLUX HIGH LEAKAGE FLUX LOW USEFUL FLUX HIGH 1 LEAKAGE FLUX LOW USEFUL FLUX HIGH STARTING STARTING TORQUE CURRENT NORMAL NORMAL HIGH LOW LOW HIGH VERY HIGH NORMAL LOW LOW LOW NORMAL FAIRLY HIGH VERY HIGH SLIP LOW LOW VERY LOW LOW MODERATE LOW FAIRLY HIGH POWER FACTOR EFFICIENCY VERY HIGH HIGH FAIRLY HIGH HIGH HIGH FAIRLY HIGH FAIRLY HIGH VERY HIGH LOW GOOD HIGH * HIGH FAIRLY HIGH FAIR Fig. 29, Different Kinds of Slot and Rotor Construction and the Results Obtained from Them order to provide a motor for polyphase circuits with practically un- limited speed variation from no load to full load, the wound rotor slip- ring motor was developed. The torque developed by this motor is practically proportional to stator current. This makes the line cur- 80 TYPES OF ALTERNATING-CURRENT MOTORS 33 rent the lowest for starting of any induction motor. The efficiency is also good at slow speeds, but power factor is low for this machine. The stator construction is standard, as in other types of polyphase motors, but the rotor has a low resistance winding which is con- nected in phases to three slip rings. The control is obtained through the use of a contactor and resistance bank connected to the rings. Fig. 30. A Squirrel Cage Three-Phase Motor with Bearing Bracket Removed Courtesy of Lincoln Electric Company Slow speeds are developed when high resistance is introduced into the rotor circuit which increases as the resistance is decreased. Slip-ring motors are available in all sizes from 1/4 to 5000 horse- power for all standard voltages. Through the control they are made reversible speed. They are used on cranes, hoists, and metal rolling mills where reversing duty is essential and where frequent stops and starts are encountered. Because this motor may be "plugged," that is reversed from one direction to the other with power directly from the line, these motors require extra heavy shaft and rotor construc- tion to withstand this abuse. Fig. 31 shows a large heavy-duty wound rotor motor for steel mill service. Fig. 32 shows a partly wound rotor. 81 34 TYPES OF ALTERNATING-CURRENT MOTORS The other method of obtaining an Multispeed Motor. alternating-current adjustable speed motor is to use a squirrel cage LAMINATED STATOR THREE SLIP RINGS- Fig. 31. A Westinghouse Type CW Heavy-Duty Wound-Rotor Induction Motor AIR DUCTS SLOT INSULATION TINNED ENDS COILS OIL SLINGER TAPE Fig. 32. A Partially Wound-Rotor Courtesy of Westinghouse Electric Company THRUST BEARING SPIDER KEYWAY rotor and wind the stator a large number of stator poles. The leads from these coils are brought out to a pole changing switch. In this way as many as two, three, or four definite speeds may be obtained. For example, a 60-cycle three-phase motor may be made to run at 82 TYPES OF ALTERNATING-CURRENT MOTORS 35 1800, 1200, 900, and 600 r.p.m. Fig. 33 shows a multispeed motor installation with controlled apparatus. Synchronous Motor. Synchronous motors, like alternating- current generators, are usually built with stationary winding and revolving field which must be excited from some source of direct current. Any alternator can be made to operate as a synchronous Fig. 33. A Multispeed Induction Motor Controlled by a Drum-Type Pole-Changing Switch Courtesy of General Electric Company motor, but trouble due to hunting effects may develop objectionable power surges on the transmission system. All synchronous motors develop this tendency to oscillate depending upon the tortional con- ditions of the load being driven. To overcome this trouble, a damper winding is placed in slots in the pole faces. This short-circuited winding very effectively eliminates hunting troubles. The synchronous motor has proved itself more efficient, operates at higher power factor, has absolutely constant speed regulation, and competes very favorably in first cost with other induction motors. It is ideally suited for a constant load where speed must be main- tained uniform under all conditions. By field control the synchro- 83 36 TYPES OF ALTERNATING-CURRENT MOTORS nous motor can be made to improve the power factor of a plant or power line and thereby reduce the cost of power, especially where the contract with the power company carries a penalty clause for low power factor. These motors are built in capacities ranging from 20 to 9000 Fig. 34. A 600 Horsepower, Synchronous Motor Having 52 Poles and Operating at a Courtesy of Electric Machinery Manufacturing Company Speed of 138 r.p.m. horsepower at speeds varying from 1800 to 60 r.p.m. All standard voltage and frequencies are met in these motors. Synchronous motors are used to drive compressors, paper mills, pumps, blowers, rubber mills, cement mills, mines, steel mills, flour mills, motor generator sets, and oil refining machinery. Fig. 34 shows a large synchronous motor operating a flour mill. The stator frames for practically all these large machines are fabricated from steel plate and welded in the same manner as alternators are constructed. 84 TYPES OF ALTERNATING-CURRENT MOTORS 37 In the past, the chief objection to the synchronous motor was its lack of starting torque. This has been overcome in various ways. The General Electric Company makes what is called the super synchronous motor, Fig. 35, so arranged that the stator is free to rotate as well as the rotor. In starting, the stator is brought up to synchronous speed and a brake is then applied which gradually slows up the revolving stator as the field is increased in speed. Fig. 35. A General Electric 400 Horse- power Type TSR Synchronous Motor. Stator Is Supported on Inner Set of Bear- ings and Rotor on Outer Set of Bearings Other companies, by special rotor design with heavy squirrel cage windings in the poles, are now able to successfully build synchro- nous motors with satisfactory starting torque. Fynn-Weichsel Motor. The Fynn-Weichsel motor, Fig. 36, developed by the Wagner Electric Co., is a combination of the slip- ring and direct-current motor. The stator has two windings dis- placed by 90 degrees. One of these windings is connected through an adjustable resistance to the direct-current brushes and the other stator coil is short-circuited with another adjustable resistance. The rotor of this motor, Fig. 37, has two independent sets of wind- ings consisting of a direct-current set of coils connected to a direct- current commutator and a three-phase winding connected to slip rings. Three-phase power is supplied to the slip rings which is the only connection this motor has to the power lines. 85 38 TYPES OF ALTERNATING-CURRENT MOTORS In starting, this machine has the characteristics of a slip-ring induction motor. As soon as the machine reaches full speed, the direct current automatically supplied to the stator field from the commutator makes it a synchronous motor. The brushes in field Fig. 36. Exterior View of Fynn-Weichsel Motor with Hinged Cover over Commutator Courtesy of Wagner Electric Corporation circuits are set so as to give the motor proper starting torque to meet the needs of the load. This motor has the advantage over the ordinary synchronous motor, being able to operate as an induction Fig. 37. Rotor of Fynn-Weichsel Motor Courtesy of Wagner Electric Corporation motor on heavy overloads, and immediately pull into synchronism as soon as the load becomes normal again. The Fynn-Weichsel motor can be adjusted to have power factor corrective effects on the line by changing the resistance in the direct-current circuit to the stator. 86 ARMATURE CONSTRUCTION TYPES OF ARMATURES Ring Armatures. Ring armatures were first used by Pacinotti in 1860, who wound the wire upon an iron ring, Fig. 1. In ring wind- ings the parts of the windings which pass through the inside of the ring do not cut any magnetic lines (assuming there is no magnetic flux Fig. 1. Partially Completed Ring-Wound Armature пог R O MOM0M61 Fig. 2. Simple Gramme Ring Winding S • passing across the opening inside of the iron ring), and, as a result, are inoperative, so far as the e.m.f. of the machine is concerned. Thus only that portion of the winding on the outer surface, Fig. 1, is useful in producing a voltage. A core of the Gramme ring type is shown in Fig. 2, and a com- 87 2 ARMATURE CONSTRUCTION plete Gramme ring armature provided with a commutator of usual form is shown in Fig. 3. Drum Armatures. The principle of the drum winding is shown in Fig. 4, and it is apparent that it is much simpler than the ring :: Fig. 3. Couple Gramme Ring Winding winding. Each wire is placed on the outside of the drum, usually parallel to the axis of the armature core, and is joined to another wire by means of connecting wires called end-connections, which do not pass through the core. The only reason for having any opening O Fig. 4. Principle of Simple Drum Winding in the core at all, other than to save the material, is to improve the ventilation and cooling of the armature. In two-pole machines the end-connections run across the ends of the core and connect wires which are almost diametrically opposite. In multipolar ma- chines the end-connections join wires which are separated by a distance approximately equal to the distance between correspond- 88 ARMATURE CONSTRUCTION 3 من ing points on adjacent poles, so that the electrical pressures in the wires thus connected will act in the same direction around the loop. The drum armature may be thought of as derived from the ring armature by moving the inner connections of the winding, or the part of the winding on the inside of the ring, Fig. 2, to the outer surface, at the same time stretching the coil so that the two sides will occupy approximately corresponding positions under adjacent poles. Disc Armatures. The disc armature differs from the other two in that the wires in which the electrical pressure is induced, instead 0 S S N a € Fig. 5. Principle of Disc Armature S of being on the outer cylindrical surface of the armature core, are placed radially on the flat sides of a disc. The principle of the disc is shown in Fig. 5. The magnetic poles N and S can be produced by permanent magnets or, as is usually the case, by electromagnets. This type of armature was never used very much. A modified form of the disk armature, Fig. 5, is the homo-polar generator armature, Fig. 6. In this armature disk a continuous direct current is produced, without the use of a commutator. A brush bears on the disk at A and shaft at B to make the electrical connections to the external circuit. The homo-polar generators are low voltage machines. The few machines that have been built were for electro- plating work, which required several thousand amperes at one or two volts electrical pressure. 89 4 ARMATURE CONSTRUCTION CONSTRUCTION OF ARMATURE CORES Purpose of Armature Core. The function of the armature core is twofold: it supports the armature winding and it carries the flux. from one pole core to the adjacent pole cores; that is, it completes the magnetic circuit between the pole pieces. On account of its high permeability and great strength, iron is by far the best material 1 A SMO Fig. 6. Homo-polar Generator Armature for armature cores. It has become the practice to build up arma- ture cores of thin, soft iron or mild steel discs, insulated from one another by varnish, rust, thin oxide, or paper. An armature core composed of such sheets, forced together by hydraulic or screw pres- sure, is found to be from 85 to 95 per cent iron, the remainder of its volume being made up of insulation, air space, etc. Core Bodies. The cores of armatures are made of laminae (thin discs) of wrought iron or mild steel. These discs are stamped 2 B 3 www Fig. 7. Order of Stamping Armature Core Segments out of sheet metal, and range from 0.014 inch to 0.025 inch in thick- ness, the former thickness being that most often used at the present time. Core discs up to about 30 inches in diameter are punched in one piece, while larger diameters are stamped out in sections, Fig. 7, and the core built up as indicated in Fig. 8, alternating the joints. 90 ARMATURE CONSTRUCTION 5 1.00 These stampings are now so accurately made that, after assembling the discs into a core, the slots need not be milled out, as was formerly necessary. Milling is most objectionable because it burrs over the edges of the discs. The burrs thus produced connect adjacent discs and facilitate the flow of eddy currents, thereby defeating the pur- pose of lamination. Turning after assembling also tends to increase the iron losses. Hence, if it is found that the periphery of the core body is irregular, it should be ground true. Fig. 8. Method of Building up Armature Core from Segments The core discs are insulated from each other either by a thin coating of iron oxide on the discs or by a thin coating of japan varnish. Sometimes shellac or paper is used for insulating these W Fig. 9. Armature Teeth with Parallel Slots laminae; but on account of the greater expense and the fact that the efficiency is only slightly bettered, these latter are applied only in special cases. Shapes of Armature Teeth. The armature cores used in practice are almost always provided with a toothed surface. Thus the arma- ture winding is protected, the length of the air gap reduced, and the winding is prevented from slipping in the core. The general efficiency of the machine is greater than when a smooth core is used. The number of teeth must be relatively large, about four per inch of armature diameter, to prevent noise and excessive eddy-current losses in the pole faces. A common form of armature tooth is slightly narrower at the root than at the top, the resulting slot having parallel sides, Fig. 9. Fig. 10 illustrates a form in which the tops are slightly extended to give a larger magnetic area at the top, thus decreasing the reluctance of the air gap and helping to retain the inductors in the slots by the insertion of a wedge of wood. The latter object is also attained by notching the teeth as in Fig. 11, in case it is not desirable to increase the area of the top of the tooth. 91 6 ARMATURE CONSTRUCTION 20 Fig. 10. Teeth with Projecting Tops www AM Binding-Wire Channels. In machines using binding wires to hold the armature inductors in the slots, it is usual to stamp some of the core discs of slightly reduced diameter so that the binding wires may be flush with the surface of the armature. The reduction is seldom more than inch on the diameter, giving a channel not more than inch deep. The width is determined by the number and the size of the binding wires. SOLUTION Fig. 12. ww 8888 VERSLAS Fig. 11. Notched Teeth to Hold a Wedge BARBARA LE wwwwwwww Forms of Armature Core Discs for Small Machines www. wwww wwww wwww www Mounting of Core Discs. Some mechanical means must be provided to hold the core discs together, and to connect them rigidly to the shaft. In the case of small cores not exceeding 15 inches in diameter, the core discs take either of the forms shown in Fig. 12. The right-hand form is preferable on account of increased ventilation. The laminae are simply keyed to the shaft, being held together under heavy pressure by end-plates of cast steel or cast iron, which are in turn pressed inward either by nuts fitting in threads upon the shaft or by bolts passing through, but insulated from, the armature discs and end-plates. Large cores in which the discs are made in sections, or for which the material of the core near the shaft is not required, are built upon an auxiliary support called a spider, which has different forms, de- 92 ARMATURE CONSTRUCTION 7 pending on the mode of attachment between it and the core discs. Fig. 13 shows the discs held together and to a skeleton pulley, or spider, by bolts passing through them, the spider being keyed to the shaft. The objection to this construction is that the bolt-holes reduce the effective area of the core, thus strangling the magnetic flux. This difficulty may be overcome by placing the bolts internal to the core, Fig. 13. Core Discs Bolted to Spider-Bolts Pass through Discs JUUUUUU as in Fig. 14, in which case they need not be so well insulated. An- other and newer arrangement provides the discs with dovetail notches or extensions which fit into extensions or notches on the spider arms, Fig. 15. The sectional view shows the method of holding the laminae together by means of bolts and end-plates, also the R extensions for supporting the end-connections of a barrel winding. D D D ▪▪▪▪▪▪▪▪ I ME OB C I Fig. 14. Core Discs Bolted to Spider-Bolts Placed Inside of Discs R SALONE. Aravata 61014 ་་་་་་་ B Fig. 15. Method of Mounting Large Armature Core on Armature Spider R 93 8 ARMATURE CONSTRUCTION The hubs of armature spiders are usually cleared out between their front and back bearing surfaces to facilitate fitting the shaft, Fig. 15; and in larger sizes the seating on the shaft is often turned to two VENTILATING DUCTS DOVETAIL NOTCHES Fig. 16. Construction of Armature Hub ارود 111111 Fig. 17. # O O O O O nuchill O • ་་ Hil ་་་ Armature Spider for Large Generator W 貝 ​""" different sizes to admit of easier erecting, Fig. 16. A spider and other features of construction of a large generator are shown in Figs. 17 and 18. The outer rim of the spider is cut in six pieces, each of which has four dovetail notches. If it is cast in one piece, trouble may arise 94 ARMATURE CONSTRUCTION from unequal strains in the metal due to contraction. Ventilating apertures or ducts are provided, and on the side of each arm, Fig. 17, are seen the seatings and bolt-holes for attaching the commutator hub and the rim which supports the winding. In Fig. 18, which shows a completed core, the supporting rim and narrow ventilating ducts are visible. Figs. 19 and 20 show two views of a completely assembled Fig. 18. Armature Core and Commutator Mounted on Temporary Shaft armature core and commutator ready for the winding; the armature spider is shown in Fig. 21. An armature core (in the process of con- struction) for a revolving armature is shown in Fig. 22; and a core (also in the process of construction) for a stationary armature, as used in alternating-current machines, is shown in Fig. 23. A completed armature core for a small machine is shown in Fig. 24. The operator is shown driving a steel key or wedge in a groove in the inner hub. This key clamps and holds the end plate to the armature spider. In many cases, the laminae are compressed tightly in a press before the key is inserted. 95 10 ARMATURE CONSTRUCTION Fig. 19. Completely Assembled Armature and Commutator Ready for Winding (Rear View) Courtesy of General Electric Company Ventilating Ducts. Armature cores heat from three causes, namely, hysteresis, eddy-currents in the iron, and I2R losses in the copper inductors. In order that the temperature-rise of the armature shall not exceed a safe figure (60°C.), it is necessary in the large and Fig. 20. Completely Assembled Armature Core and Commutator Ready for Winding (Front View) Courtesy of General Electric Company 96 ARMATURE CONSTRUCTION 11 Fig. 21. Armature Spider for Armature Shown in Figs. 19 and 20 Courtesy of General Electric Company heavy-duty types to resort to means of ventilation, usually ducts which lead the air out between the core discs. When the length of the armature core exceeds about four inches, the armature core is divided into equal sections by radial ventilating ducts. Enough ducts should be used so that the length of each section will not be more than Fig. 22. Armature Core for Revolving Armature in Process of Construction Courtesy of Allis-Chalmers Company 97 12 ARMATURE CONSTRUCTION Fig. 23. Armature Core for Stationary Armature in Process of Construction Courtesy of Allis-Chalmers Company three inches. These ventilating ducts are usually from to inch wide. The narrow duct is used on the small-diameter, high speed machine, and the wide duct on the large-diameter, slow speed machine. There is always a ventilating duct at each end of the arma- Fig. 24. Complete Armature Core for Small Direct-Current Machine Courtesy of Reliance Electric and Engineering Company 98 ARMATURE CONSTRUCTION 13 ture laminations in all except the very small machines. To keep the core discs apart at these ducts, it is necessary to introduce distance pieces, or ventilators. Fig. 25 illustrates some of these devices. At A are shown simple pieces of rolled-steel, of I-beam or T cross-section, spot welded radially at intervals to a special core disk that is 3 to 4 times the thickness of the usual laminae. This form fails to provide adequate support for the teeth, a dif- ficulty obviated in the form shown at B, where the spacer extends nearly to the tip of the teeth. Additional strength is obtained by placing a crimp or bend in the long spacers shown at B, Fig. 25. A 11001 Fig. 25. Different Types of Distance Pieces of Ventilators www ALBANUNUNOL B Binding Wires. With toothed-core armatures the inductors may be held in the slots by wedges of wood, Figs. 10 and 11, or by bands of wire wound around the armature core. These binding wires must be strong enough to resist the centrifugal force which tends to throw the armature inductors out of the slots, and yet must occupy as little radial space as possible, in order not to interfere with the clearance between the armature and the pole pieces. The common practice is to employ a tinned wire of hard-drawn brass, phosphor bronze, or steel, which, after the winding, can be sweated together by solder into one continuous band. Under each belt of binding wire, placed over the ends of the armature conductors at each end of the core, a band of insulation is laid. This usually consists of two layers: first, a thin strip of vul- canized fiber or of hard red varnished paper slightly wider than the belt of wire, and then a strip of mica in short pieces of about equal width. Sometimes a small strip of thin brass, with tags which can be turned over and soldered down, is laid under each belt of binding wire to prevent the ends of the binding wires from flying out. Wedges. At the present time, it is the customary practice to use either a partially closed slot, Fig. 10, or the open slot, Fig. 11, 99 14 ARMATURE CONSTRUCTION on all modern machines. With the open slot, a notch is cut in the side of the slot in order to hold the wedge, which can be inserted after the armature coils are in position in the slots. 3 In the small armatures of fractional horsepower motors, the wedges are made from vulcanized fiber about to inch in thick- ness. These wedges are driven into the notches in the side of the teeth from one end of the core, Fig. 24. In this illustration, the operator is not driving a wedge in a slot but is fastening or driving a steel key in the armature core spider in order to fasten the end plate to the armature spider. The wedges used to hold armature coils in slots are also made of well baked hardwood, such as maple, and are shaped to fit the spaces provided for them as shown in Figs. 10 and 11. In some cases, specially prepared wedges are used, being treated with bake- lite and other substances to give them greater mechanical strength and insulating properties than wood or fiber. In the armatures of the machines at speeds of 1200 revolutions per minute and less, and in the smaller sizes when the weight of the conductors in the slots is not excessive, these wedges are used to withstand the action of centrifugal force and hold the coils firmly in the slots. In the larger size armatures and in those of greater diameter or operating at higher speed than 1200 revolutions per minute, it is also necessary to use band wires around the core and on top of wedges in order to hold the coils in the slots. 1 ठ Ad COMMUTATOR AND BRUSH CONSTRUCTION Commutator Bars. Commutator bars are almost always made of copper; other metals, such as brass, iron, or steel, are not satis- factory on account of pitting and burning. Rolled or hard-drawn copper is preferable, because of its toughness and uniform texture; but in some cases, on account of the shapes necessitated by different methods of connection to the armature conductors and various clamp- ing devices, the segments are either cast or drop-forged, the latter being at present the type used more often on large machines. In order to secure a good fit, the cross-section of the bars should be properly tapered according to the number of segments that makes up the whole circumference. It is obvious that if the number of segments equals 360, each segment plus its insulation (on one side) S 100 ARMATURE CONSTRUCTION 15 should have a taper of 1 degree; while if the number of segments equals 36, the taper would be 10 degrees, Fig. 26. It is not practicable, how- ever, to use mica insulation that has not parallel faces; hence the copper segment is tapered, and any defect in the taper of the copper segment cannot be made good with insulation. It is not practical to RISER COPPER BAR -10°TAPER B ·MICA Fig. 26. Commutator Bars B Fig. 27. End Insulating Ring of Commutator make the thickness of the commutator segment at A, Fig. 26, less than 0.100 (about 2) inch or less than .060 (1) inch at B. It is found, however, that when the number of segments exceeds 150, bars of the same taper can be used in constructing a commutator having either two more or two less than the designed number. Insulation. It is important to have good insulation between each bar and its neighbor. Especially good insulation is required between the bars and the sleeve or hub around which they are mounted, as well as between the bars and the clamping devices that hold them in place. The voltage between bars is not as great as that between the bars and the metal-work of the machine. It is essential that the in- sulating material be such that it will not absorb oil or moisture; hence, asbestos, plaster, and vulcanized fiber should not be used The end insulation rings may be of mica, or micanite, or, if for low + 101 16 ARMATURE CONSTRUCTION 1 voltage, of that preparation of paper pulp known as press-board or press-spahn. The conical rings, used to insulate the dovetails on the bottom of the bars from the hub, are usually built of micanite molded under pressure while hot. Fig. 27 illustrates such an end-ring, cut away to show its section. Commutators using air gaps between the segments as insula- tion have been tried; but, excepting in the case of arc-lighting HUB- STEEL V-RING MICA CLAMPING RING COPPER SEGMENTS O Fig. 28. Common Method Used for Commutator Construction for Small Machines machines where the segments are few in number and the air gap large, they have not proved successful, owing to the difficulty of keeping the gaps free from metallic dust. It is of importance that the mica selected for insulating the bars from one another should be soft enough to wear away at the same rate as the copper bars, and not project above the segments. Amber mica, soft and of rather cloudy color, is preferred to the harder, clear white or red Indian variety. The usual thicknesses used are as given in Table I. Commutator Construction. For small machines two common constructions are shown in Fig. 28. The commutator segments 102 ARMATURE CONSTRUCTION 17 MICA EXTENDS" BELOW BOTTOM OF BARS MICA SEGMENTS 035" THICK MICA COLLAR EXTENDS 58" JOINT HERE MADE OIL-TIGHT WITH OIL-PROOF COMPOUND CORNERS OF BARS ARE ROUNDED CAP SCREW HEADS ACCESSIBLE FROM OUTSIDE ANGLE AT V IS 30° GIVING A. GOOD GRIP ON THE BARS LARGE SOLID RISERS Pe" CLEARANCE BETWEEN BOTTOM OF BAR AND COMMUTATOR SLEEVE COMMUTATOR SLEEVE MICA COLLARS EXTEND AROUND BOTTOM OF BARS BOTTOM OF BAR IS ROUNDED Fig. 29. Commutator for Small Machine Cut Away to Show Construction Courtesy of Reliance Electric and Engineering Company Less than 1000 Less than 300 Less than 150 0.035 to 0.060 in. 0.025 to 0.040 in. 0.020 to 0.030 in. 0.100 to 0.160 in. 0.080 to 0.130 in. 0.040 to 0.100 in. Voltage of Machine Segments Between Neighboring Device Segments and Clamping Shell and between Between Segments and THICKNESS OF MICA Thickness of Commutator Insulation TABLE I 103 18 ARMATURE CONSTRUCTION are secured between a bushing or hub and a clamping ring, the latter being mounted on the hub, and forced to grip the bars by means of a nut on the hub or by bolts passing through the ring and hub, as in Fig. 29. The ends of the bars are beveled so that the ring and Fig. 30. 1078000 FILTE 111111 GALERIETATE Commutator Construction for Large Machines. Commutator Spider is Bolted to Armature Spider Fig. 31. Commutator Construction for Large Machines. Commutator Spider Is Mounted on Armature Shaft Independent of Armature Spider bushing draw the segments closer together by tightening bolts. The hub in small machines is usually of cast iron, Fig. 28, keyed to the shaft; but in large machines the commutator is built upon a strong flange-like support or shell, bolted to the armature spider, Fig. 30, or mounted on a separate spider secured to the shaft, Fig. 31. When drawn copper strip is used for commutator segments, the 104 ARMATURE CONSTRUCTION 19 INSULATING VARNISH APPLIED HERE AND BAKED ON Fig. 32. Method of Constructing and Forming Small Commutator Courtesy of Reliance Electric and Engineering Company design should be such that the available surface for the brushes takes up nearly the whole length of the bar, and the beveled ends should be as simple as possible. With drop-forged segments this is not so im- portant. In building commutators it is usual to assemble the bars to Fig. 33. Method of Constructing and Forming Large Commutator Courtesy of General Electric Company 105 20 ARMATURE CONSTRUCTION the proper number, with the interposed pieces of mica, clamping them temporarily around the outside with a strong iron clamp, as shown in Figs. 32 and 33, or forcing them into an external steel Fig. 34. Commutator Shell or Spider and Clamping Ring for Large Commutator Shown in Fig. 33 Courtesy of General Electric Company ring under hydraulic pressure. They are then put into a lathe and the interior surface is turned or bored out to form a V-groove, Fig. 33. Both ends are turned up in the same way to form V-grooves DOODD Fig. 35. Mica Insulating Rings for Commutator Shown in Fig. 33 Courtesy of General Electric Company which will receive the clamping pieces. The whole is then mounted with proper insulation upon the sleeve, and the clamping end-pieces are screwed up, Fig. 29. It is then heated and the clamps still further tightened up, after which the temporary clamp or ring, Figs. 32 and 106 ARMATURE CONSTRUCTION 21 Fig. 36. Completed Commutator for Small Machine Courtesy of Reliance Electric and Engineering Company 33, is removed and the external surface turned up. The commutator shell or spider and clamping ring for a large commutator are shown in Fig. 34, and the mica insulating rings for same are shown in Fig. 35. Two completed commutators are shown in Figs. 36 and 37. Fig. 37. Completed Commutator for Very Large Machine Courtesy of Allis-Chalmers Manufacturing Company 107 22 ARMATURE CONSTRUCTION 1516 Figs. 38 and 39. Methods of Connecting Commutator Risers to Commutator Bars Commutator Risers. Connection is made with the armature inductors or conductors by means of radial strips or wires, sometimes called risers, which are inserted into a cut at the corner of each bar Fig. 40. Armature Winding Connected Directly to Commutator Bar !!!!! Fig. 41. Methods of Connecting Armature Winding to Commutator Risers and firmly held there by a screw clamp and solder. Figs. 38, 39, and 40 illustrate various modes of making connection to the commu- tator bar. The risers are connected to the armature winding in several different ways as indicated in the top part of Fig. 41. The 108 ARMATURE CONSTRUCTION 23 methods of attaching the risers to the commutator bars are shown in the lower part of Fig. 41. In some evolute windings no risers are needed, the ends of the evolute being fastened directly to the com- mutator bars. Similarly, in the case of drum-wound armatures, no Fig. 42. Several Different Forms of Carbon Brushes =24111** Fig. 43. Methods of Attaching Flexible Stranded Shunts to Carbon Brushes risers are needed if the commutator diameter is very nearly that of the armature. Brushes. Carbon brushes are almost the only type that is now used. Their shape depends upon the type of brush holder selected, and upon whether the brushes are applied to the commutator 109 24 ARMATURE CONSTRUCTION radially or at an angle. Some of the various shapes and forms of carbon brushes are shown in Fig. 42. These are usually clamped or bolted to the brush holder arm which conducts the current to them. It often is desirable to have a flexible copper wire or cable to carry the current to the carbon brushes, Fig. 43. These shunts (or pigtails as they often are called in practice) are composed of a large number of very small wires twisted together, in order to be very flexible. These shunts may be attached to the brushes by several different methods. At the left, Fig. 43, a large copper washer, soldered to the end of the shunt, is fastened to the carbon brush by a hollow eyelet type rivet. In the center picture, Fig. 43, a hole is drilled in the carbon brush and filled with a soft solder into which the tinned end of the shunt is inserted. This solder is of such composition that it expands when it cools, thus forming a good tight connection. In the right- hand picture, Fig. 43, the copper shunt is clamped and soldered to tinned copper strips. These copper strips are clamped to the carbon brush by two tubular rivets. Brush Holders. The mechanism for holding the brushes must fulfill the following requirements: (1) The brushes must be held firmly against the commutator, but allowed to follow any irregularity in the contour of the latter without jumping away. (2) The mechanism must permit the brushes to be withdrawn while the commutator is rotating, and must feed them forward as required. (3) Spring pressure must be adjustable, and the spring must not carry current. (4) The springs must not have too great inertia, or they will not readily fulfill the first condition in regard to following the commutator. (5) Insulation must be very thorough. (6) The mechanism must be so arranged that the position of the brushes may be shifted. (7) All parts must be firm and strong, so the brushes will not chatter as the result of vibration while the machine is running. The commercial forms of holders for carbon brushes may be classified under three types: hinged structures, parallel spring holders, and reaction holders. Fig. 44 illustrates a hinged brush holder, and an arm holding 110 ARMATURE CONSTRUCTION 25 several. The carbon moves in a light frame, being held against the commutator by a spring whose tension may be adjusted. Connection เทออก LILL Fig. 44. Brush Rigging and Hinged Brush Holder is made between the brush and the arm by means of a flexible lead, tinned and laid in a slot in the upper part of the carbon. A metal cap placed over the top and sweated in place makes a permanent contact. This is shown by the two illustrations of the brush. S 9 C B A C 1AM Fig. 45. Reaction Type of Brush Holder A reaction type brush holder that has been used quite extensively on the older motor and generators is shown in Fig. 45. The carbon brush C is pressed against the commutator by finger A which is 111 26 ARMATURE CONSTRUCTION operated by spring L. The brush holder B is secured to the brush rocker arm P by means of a set screw q. It is very important that each end of the brush be beveled at the correct angle. The brush must not be too long or it will raise the finger A so high that the brush will be thrown away from the face of holder B. The troubles encountered with this type of brush holder were usually due to failure to observe the above facts. CARBON BRUSH FINGER SHUNTS SPRING BRUSH HOLDER Fig. 46. Type of Brush Holder Courtesy of Allis-Chalmers Manufacturing Company, Milwaukee, Wisconsin Another type of brush holder is shown in Fig. 46. It is called the box type and is usually made of cast brass or copper. The open- ing for the carbon brush is machined to very exact dimensions, in order that the brush may slide freely in the holder and at the same time not have so much clearance that the brush will wobble or shift its surface and position on the commutator. The pressure exerted by the finger on the carbon brush can be increased by moving the end of the spring up to a higher notch. The flexible stranded wires called "shunts," Fig. 46, are used to pro- vide a lower resistance path for the current from the commutator and brush to the brush holder than that obtained between the sides of the carbon brush and the holder. The machine surface A, Fig. 46, of the brush holder is bolted to the brush rocker arm. Rockers and Rocker Arms. The type of rocker arm used on small machines, 50 horsepower or kilowatt and less, is shown in 112 ARMATURE CONSTRUCTION 27 Fig. 47. It is clamped around a shoulder turned upon the hub of the bearing bracket, Fig. 48. The brush holders are fastened to the right-hand end of the long copper or brass rod, called the brush holder stud, which the assembler has in his hands, Fig. 47. The brush holders and studs are insulated from the brush rocker arm by large Bakelite or Micarta washers. First, tighten the nut at the left, مار tec Allow BG-10 DANE Figs. 47 and 48. Brush Rocker Arm for Small Machine and Method of Mounting Same on Bearing Pedestal Courtesy of Reliance Electric and Engineering Company Fig. 47, then clamp the brush holder stud securely to the sides of the slot in the rocker arms. Some manufacturers machine a square shoulder on that part of the brush holder stud which fits in the slot of the rocker arm, Fig. 47. Then a square insulating tube is slipped over this portion of the rod and the insulating washers with square holes on the inside are placed over this tube. This construction holds the brush holders more firmly in posi- tion on the commutator, with less tendency for the brush holder stud to turn, should the nut at the left loosen up in service. The reaction from the spring tension on the carbon brushes tends to turn the brush holder stud in the slot in the rocker arm and thus loosen the nut. 113 28 ARMATURE CONSTRUCTION After the machine is assembled and tested, the proper position of the brush rocker arm on the bearing bracket is marked. The right hand in Fig. 48 is pointing to this mark. Fig. 49. A Two-Pole Brush Rocker Arm Fig. 50. A Four-Pole Brush Rocker Arm Courtesy of Allis-Chalmers Manufacturing Company, Milwaukee, Wisconsin ROCKER RING ROCKER ARM INSULATION POLE BRUSHES TERMINAL LEADS TERMINALS BUS RINGS ROCKER SCREW BASE Fig. 51. Rocker Ring and Brush Mounting Each manufacturer will use a slightly different method or design in supporting the brushes, but the principle of all of them is similar. In Figs. 49 and 50, slots are provided in the brush rocker arm so that 114 ARMATURE CONSTRUCTION 29 F the brushes can be shifted to proper position on the commutator and then held securely in place by bolts to the bearing bracket or bearing pedestal. These parts are made quite large in proportion to the stress or strain that they will receive in order that the brushes will not be displaced from their correct position by even a few thousandths part of an inch. It is good practice always to use two or more brushes in parallel with each other, instead of one large brush. Then if one brush fails. to make good contact on the commutator or sticks in the holder, the other brush will carry the current while it is being cleaned or re- placed. On large multipolar generators, the armature is supported by bearings which are not attached to the frame. Instead, a steel rocker ring, Fig. 51, is clamped to the frame with bolts. The rocker arms which support the brushes and brush holders are fastened mechanically to this rocker ring for support but electrically insulated from it. An electrical connection is made from the rocker arm to one of the two copper bus rings. These copper bus rings are wrapped with black insulating tape after the electrical connections are com- pleted. A ring of insulation, to which the ends of the rocker arms are bolted, is used to hold the ends of the rocker arms securely in place and an equal distance apart. The position of the brushes on the commutator can be shifted by turning the rocker screw, Fig. 49. The type of brushes and brush holder used in Fig. 49 is similar to those shown in Fig. 46. The surface A, Fig. 46, is bolted to the ma- chined surface of the brush rocker arm. 115 BRUSH HOLDER BEARING- TERMINAL COVER PULLEY-END BEARING BRACKET TERMINALS A FAN POLE TIP ARMATURE TOR COMMUTATOR- FRONT BEARING BRACKET FIELD COIL INTERPOLE COVERS DISMANTLED VIEW OF A 20-HORSEPOWER, 1,150 R.P.M., 230-VOLT, DIRECT-CURRENT MOTOR Courtesy of Allis-Chalmers Manufacturing Company, Milwaukee, Wis. ARMATURE WINDING DIRECT-CURRENT ARMATURES INTRODUCTION Winding Terms. Owing to the lack of standardization of terms used by armature winders, there is much variety in the naming of common things and processes. There are many cases in which two or three different terms are used to express the same meaning. Because of this confusion in names, a winder who has secured all his experience at one shop and on one particular kind or type of machine may have considerable difficulty in producing satisfactory work in another shop. A thorough understanding of the use of different materials and fundamental principles will enable him to adapt himself easily to changed conditions. Types of Armature Windings. There are two general types of armature windings, the open circuit and the closed circuit. The open-circuit winding is used on alternating-current generators and the ends of the winding are connected to collector rings or to the external system. (The open-circuit system was used on the first direct-current generators constructed. The two ends of the coil were connected to commutator bars that made contact with the brushes only when the coil generated its maximum voltage. There was no current flowing through the coil except when it was con- nected by the brushes to the external circuit.) In the closed-circuit type all the armature coils are connected in series with each other at the commutator bars, and the voltage generated by all the coils is thus added together. This type of winding produces a higher voltage, with the same number of armature conductors or coils, than the open-circuit direct-current type of windings. For this reason it is used on practically all direct-current machines manu- factured at the present time. RING ARMATURE Use of Ring Armature. entirely to generators from The ring armatures are limited almost kw. to 2 kw. in size and are usually 117 ARMATURE WINDING directly connected to small steam turbines. These outfits are used for lighting purposes on locomotives, steam shovels, oil-well machines, ore handlers, in lumber camps, and similar outdoor work where they are subjected to very rough usage and are handled by those who are not familiar with electrical machinery. A view of such an armature is shown in Fig. 69. Winding Ring Armature. Before starting to wind an armature it is always necessary to remove any sharp burrs or fins which may exist in the slots of the core. Failure to watch this detail will allow the sharp edge of the laminations to cut through the insulation and "ground" the windings, making it necessary to spend additional time in locating the defective coil. In winding this type of ar- mature one end of the wire is attached to the commutator and the other end is passed through the slot and through the inside of the core, then through the slot again, and so on until the desired number of turns have been wound around the core. The end of the wire is then attached to the adjacent commutator bar. The beginning end of the next coil is attached to this commutator bar and the coil in the next slot is wound in the same manner as in the first slot. This operation is repeated for each slot. The ending end of the coil in the last slot is connected to the same commutator bar as the beginning end of the first coil. When the amount of wire needed for one slot is determined, the correct length is wound on a shuttle or bobbin which can be easily passed under and over the core of the armature. The commutator should be located on the shaft so that the center of the bar is opposite the center of the slot in the core. Fig. 69. Ring Armature for a Direct- Current Generator Courtesy of the Pyle-National Company In winding these armatures asbestos-covered wire is frequently used, instead of cotton-covered wire, in order to produce a machine that will withstand a higher temperature and not burn out as easily as the ordinary machine. When asbestos-covered wire is used, the leads should be soldered to the commutator bars with a special 118 ARMATURE WINDING 3 solder, which has a much higher melting point than the ordinary solder. When ordinary solder, which is composed of half tin and half lead, is used, the temperature may become high enough to cause it to loosen up and be thrown out from the bars. This makes a poor contact and causes great heating, and in time the leads and commutator bars become red-hot and destroy the machine. The 32-volt armatures instead of being wound with wire are frequently wound with a copper ribbon nearly as wide as the slot. The slots are usually lined with mica, fish paper, or asbestos paper in order to protect and insulate the windings from the core. The completed armature is often dipped in bakelite varnish. This not only makes the armature winding acid-proof, salt-water proof, and moisture proof, but it also enables the winding to operate at a higher tem- perature. The bakelite varnish fills up all air pockets in the winding and allows the heat to be conducted from the copper out through the insulation and radiated to the air. DRUM ARMATURES ARMATURE COILS There are two distinct types of drum windings or coils used on direct-current armatures-the wound type and the formed type. Wound Type. In the wound type the correct number of turns are wound by hand or machine directly into the slot. This winding is used on small motors and generators usually of less than 1 horse- power output. The number of slots on such an armature are small, usually less than 20, and the number of turns or conductors will be great and will range from 10 to 100 or more. Formed Type. In the formed type of winding the conductors are wound on a form and are bound together by means of tape into one coil which is then inserted in the slots. This winding is used on nearly all motors and generators larger than 1 horsepower. The conductors are formed from round and square wire, strap, ribbon and copper bars. Diamond Coil. This coil derives its name from its shape, which is similar to a diamond, as will be noted by referring to Fig. 70 and the center group of coils in Fig. 71. This type of coil is used more extensively than any other type of coil. The great advantage of this coil is that it can be easily manufactured in large quantities 119 4 ARMATURE WINDING for standard machines. These coils are all of like size and shape and are symmetrical, and there is no tendency for electrical unbalance to occur. When a wave winding or connection is used in winding a Fig. 70. Diamond Type Armature Coil direct-current armature, the leads are brought out from the straight portion of the coil as shown in Fig. 70. The leads from the coil are brought out near the point of the diamond, as shown in the center Hon Fig. 71. Concentric and Diamond Type Armature Coils coil, Fig. 71, when the coil is used on the stator or phase-wound rotor of an induction motor and on a direct-current armature when a lap or multiple connection is used. The conductors are usually first wound on a form in the shape of a long loop or hairpin, as shown at A in Fig. 72, and then pulled by means of a coil spreader into the form shown at B. This particular coil is three wires wide 120 ARMATURE WINDING 5 10 and has 5 turns. When there are two or more wires in parallel, square, double cotton-covered wire is frequently used instead of round wire, because a size smaller wire can be used and more space will be available for insulation. B Involute Coil. The involute coil is used mostly on direct- current industrial motors, low-voltage electroplating generators, and the rotors of induction motors. This type of coil is shown at C, Fig. 72, with the leads brought out at the point of the involute. A Fig. 72. Hairpin Loop, Diamond, and Involute Coils C The leads can be brought out at the straight part of the coil in the same manner as the diamond coil. It is not easy to insulate these coils properly, due to the number of bends in the coil, and the bends make it difficult to place the coils in the slots of the core. The bar type of coil with involute end connectors is easy to insulate and assemble and is used more extensively than the wire-formed coil. The great advantage of the involute coil is that less space is required for end connections than in any other type of coil and therefore it is used when the armature must be made as short as possible. The involute coil can be punched in one piece from a sheet of brass or copper. It is used extensively on the rotors. of induction motors driving electric elevators. A view of this coil is shown in Fig. 73. Fig. 73. Punched Involute Coil Courtesy of Roth Bros. and Company Concentric Coils. The simplest and easiest coil to wind and insulate is the concentric coil shown on the left and right in Fig. 71. The disadvantage of using these coils is the fact that several different sizes are required on the machine; and on all except single-phase machines some of the coils must be bent into two or three different 121 6 ARMATURE WINDING shapes. This makes it necessary to provide several different forms and molds for winding and shaping the coils. They are not inter- changeable and, due to this fact, the number of spare coils necessary for repairs is greatly increased making the cost of manufacture and repair more expensive than with the other types of windings. When A B C Fig. 74. Concentric Coils for Partially Closed Slots concentric coils are used on partially closed slots, each coil is shoved through from the end, and the end connectors are soldered on when the coil is in place. In Fig. 74 a view of the straight shoved-through type of coil is shown at A. B and C show coils bent at one and both ends. The coils used for the partially closed slot are of heavy copper Fig. 75. Chain Winding on a Section of G. E. Stator ribbon or bars, but round or square wire or thin ribbon is used for the open-type slot. When straight coils and those bent at one or both ends are used in the same machine, the combination is often referred to as a chain winding, Fig. 75. Threaded-in Coils. The threaded-in type of coil is used very extensively in winding the stators of induction motors because it is 122 ARMATURE WINDING desirable to use the partially closed slot in order to secure as high an efficiency and power factor as possible on this type of motor. The shuttle type of coil is shown in Fig. 76 which also shows that only the ends of the coils are insulated with cotton tape. This Fig. 76. Shuttle Type Coil method of insulation allows a few wires of the coil to be passed into the slot at one time. This coil is similar to the coils shown in Figs. 70 and 71 with the exception that only the ends of the coil outside the core are taped. Forming Coils. The diamond and involute coils are usually wound in the shape of a hairpin or long loop and then pulled into 午 ​Fig. 77. Coil Spreader or Former Courtesy of the Armature Coil Equipment Company the proper shape and size by means of a coil spreader or former, Fig. 77. These machines are adjustable so that the coil will be formed to the same radius as the center of the armature teeth of the core and will have the correct dimensions between the two sides of the coil. After the machine has been adjusted to give the desired coil, any number of coils can be spread or made and they will all be interchangeable. This adjustable machine is advantageous in wind- 123 8 ARMATURE WINDING ing a number of armatures of the same size. In small shops, where there is not sufficient work to justify the purchase of such a machine, the coils may be pulled to shape by hand. This can be accomplished by using two hardwood blocks about 2 inches square and an inch longer than the length of the core with grooves cut lengthwise of the blocks. The depth of the grooves is inch and the width the same as that of the coil. The first block is fastened in a bench vise and the coil is then slipped into the groove. The coil is spread to the proper distance by pulling on the second wood block with both hands. The desired angle for the sides of the coils is made by pull- ing this coil above or below the center line of the side of the coil held in the vise. It is usually necessary to make several trials before the correct spread of coil is obtained. The best method of forming the concentric, basket, or shuttle type of coils is to wind them on a form or mold, such as is shown in Fig. 78. The former is usually made of hard fiber and attached to B Fig. 78. Wood Coil Former } a maple board about an inch or two larger than the former. Another board or plate, the same size as the maple board, is clamped to the other side of the former by means of the center bolt. This forms a groove in which the wire is wound and gives the coil its correct form or shape. A saw-cut slot is made at the corners of the plates radially inward to the edges of the hard fiber former so that short lengths of cord or wire can be inserted in these slots before winding the coil. The wires of the coil may be held in place by tying the cord or wires after the correct number of turns have been wound on the former. The front plate or board of the former is then unclamped and re- moved, allowing the coil to be slipped off easily. The width of the groove, which is the thickness of the hard fiber former, is the height of coil in the slot and is determined by the designer of the machine. 124 ARMATURE WINDING 9 INSULATING MATERIALS Insulated Wire. The wire or ribbon used in winding coils has an insulating covering of cotton, silk, enamel, or a combination of these. On motors and generators larger than 1 horsepower, double cotton-covered wire or ribbon is used almost entirely; but if the space in the slot for the copper conductors is small, single cotton enamel covered wire is used. Enamel, single silk enamel, or double silk-covered wire is used on fractional horsepower motors. In in- sulating coils and slots it is necessary to provide for both mechanical protection and electrical insulation. The insulation placed in the slot is intended to afford mechanical protection and the insulation on the coil is more for electrical insulation than mechanical protection. In the following paragraphs the most common materials used in insulating armature coils and slots are discussed. Cotton Tape. This tape is made from a medium grade of cotton and has either a smooth or twilled weaving. It has a soft, starch- less finish and is specially treated so it will absorb insulating var- nishes and compounds. Its usual thickness is 7 to 10 mils (.007 to .010 inch). Linen Tape. A good grade of cotton, which has a hard finish and looks like linen, is used to make these tapes. If linen is used in their manufacture, they are known as "Real Linen Tape" or "Irish Linen Tape." Varnished Cloth. This is a cotton cloth that has been treated with an insulating compound, varnish, or linseed oil, which improves its insulating properties. Often it is called varnished cambric, varnished muslin, empire cloth, or Kabak cloth. Cut into tape widths, varnished cloth is sometimes referred to as linotape. The tape is cut so the threads will be straight or on the bias. The bias- cut tape is more elastic than the straight tape but has only about one-half the tensile strength. The treated cloth and these tapes are made in the usual thickness of 7 and 10 mils. Paper and Fibers. Express parchment paper, red rope paper, fish paper, pressboard, horn fiber, rawhide fiber, and leatheroid are some of the different kinds of paper insulating materials used in armature winding. The express parchment paper is a high-grade wood pulp paper, free from pinholes or any metallic particles. It is made 5 and 10 mils thick and is used extensively in insulating ribbon 125 10 ARMATURE WINDING 6 4 16 or bar armature conductors. Red rope paper is made of a long- fiber, all-hemp material and does not contain any wood fiber. Cotton rag stock or material, which is very tough and will stand more bending, creasing, and abrasion than any other insulating paper, is used to make fish paper. Horn fiber is made of strong hemp stock or material. The 5- and 10-mil thicknesses are used extensively for lining the slots and the to-inch thicknesses as separators, or spacers, between the different coils in the same slot. The to 1% 32 thicknesses are used as top sticks or slot wedges to retain the coils. in the slots. Rawhide fiber and leatheroids are very similar to horn fiber except that the rawhide fiber is subjected to a greater pressure in manufacture and is a harder material and not as flexible as horn fiber, but their uses are similar. All these paper insulations can be treated with various insulating compounds, which make them more flexible when first treated. This flexibility allows the coil to be bent to any desired shape. After the varnish or insulating compound has dried, it becomes a hard, dense mass. Slot and Coil Insulation. The best practice is to insulate both the coils and the slots before inserting the coils. The advantage of this is that insulation which will resist abrasion can be used in the slot to protect the coils from the sharp edges of the laminations of the core, and insulations with high electrical qualities may be used on the coils. The coil is usually insulated when the wires can be uniformly arranged in the slot. It is not necessary to use as thick a slot insulation with an open slot core as when the threaded-in type of coil is used on an armature having a partially closed slot. In the latter case the maximum slot insulation given in the following table should be used. S Operating Voltage 6 to 50 50 to 250 250 to 500 500 to 1000 1000 to 1500 Slot Insulation .010 to .025 .010 to .035 .020 to .045 .030 to .060 .040 to .075 KINDS OF WINDINGS Lap Winding. A lap winding derives its name from the fact that the leads or ends of the coils, connected to the commutator bars, 126 ARMATURE WINDING 11 2 3 4 lap back toward each other and are usually connected to adjacent bars. It will be seen in Fig. 79 that leads from the coils in slots 1 and 5 are connected to commutator bars 1 and 2. The dark lines represent the bottom part of the coils and the light lines the top part of the coils. When the armature winding is completed, only the top part of the coils can be seen. Frequently this winding is referred to as a 1 to 2 connection, but a better name for it is multiple, or parallel, winding, because there are as many circuits from the positive to the negative brushes as there are field poles. Multiple, or parallel, winding requires as many sets of brushes on the com- 115 16 18 10 11 12 8 9 10 3 4 567 Fig. 79. Diagram of Connections for a Lap Winding 2 13 15 له 19 10 = 12 Fig. 80. Diagram of Connections for a Wave Winding mutator as field poles and the connection is sometimes referred to as a 4-brush (4-B) or 6-brush (6-B) connection, when used on a 4-pole or 6-pole machine. Wave Winding. The zigzag or wave-like shape of the coils or the armature gives the wave winding its name. This is shown very well in Fig. 80, but it must be remembered that on a completed armature only the light-colored coils can be seen. The winding is often referred to as a series, or two-circuit, winding because half of the armature coils are connected in series and the two halves are in parallel with each other. There are only two current paths through the armature winding and only two sets of brushes are necessary regardless of the number of poles on the machine. This connection is also frequently called a 2-brush (2-B) connection. In actual practice there are usually as many sets of brushes on the commutator as there are field poles in order to reduce the amount of current that each brush must carry. In Fig. 80 it will be seen that the coil in slots 1 and 5 is connected to commutator bars 1 and 9. The next 127 12 ARMATURE WINDING coil in the circuit would be in slots 9 and 13 and connected to bars 9 and 17. This type of winding is used on all railway motors and on machines of small and medium size, when it is desired to keep the number of coils to a minimum. COIL PITCH AND COMMUTATOR PITCH The coil pitch or the winding pitch is the distance spanned by the two sides of a single coil. It is usually given in the number of slots spanned or the slot numbers in which the sides of the coil are placed. In Figs. 79 and 80 the coil pitch is 4 slots and is referred to as a 1-5 pitch. When referring to a complete armature winding diagram, the coil pitch is often expressed in the number of coil sides spanned by the coil. It is easier and less confusing for the armature winder to have the coil pitch or throw of the coils expressed in the slots in which the coil is placed. The distance between the centers of two adjacent field poles is called the pole pitch. When a coil spans this distance it is called a full-pitch coil. The distance ex- pressed in the number of armature slots spanned is equal to the total number of slots on the armature divided by the number of poles. Assume, for illustration, that a certain 4-pole machine has a 44-slot armature. The full coil span would be 44÷4 or 11 slots or a 1-12 throw of coil. If the coil throw should be made 1-11 or 1-10 it would be called a fractional-pitch, short-pitch, or short-cord winding. The fractional-pitch winding is used very extensively because the length of the end connectors of the coils are reduced, armature re- action is reduced and, in an alternating-current generator, a sine wave is more nearly obtained. The commutator pitch is the distance spanned by the leads to the commutator bars. It is expressed by giving the number of the bars to which the leads from one coil are connected. In Fig. 79 the throw of the leads or commutator pitch is 1-2 while in Fig. 80 the pitch is 1-9. In a lap winding the commutator pitch is usually 1-2, 1-3, or 1-4 while in the wave winding the pitch is always much greater, being equal to the number of commutator bars+or-1 divided by the number of pairs of poles. ELECTRICAL DATA There are a number of different methods of conveying the desired armature winding information or data which vary from the 128 ARMATURE WINDING 13 simple tag shown in Fig. 81 to a very elaborate drawing. Where a special connection is desired, such as is necessary when the brushes are located between the pole pieces instead of on the center line of the poles, a drawing is almost necessary. Fig. 82 gives the same data as Fig. 81 but, in addition, shows how to locate the commutator in relation to the winding in the slot. This style of con- nection is used extensively when the brushes are located under the center of the field poles as shown in Fig. 82. The dotted line from slots 2 to 6 shows the location of the field pole and its relation to the position of the brushes. The heavy dotted line represents the part of the coil in the bottom of the slot and the full line is that part of the coil in the top of the slot. 12 19 WINDING SMALL ARMATURES Kind of Wire. The majority of small arma- tures used on electric fans and household appliances have the insu- lated wire wound directly in the slot by hand or by machine. These armatures are usually less than 4 inches in diameter, have from 10 to 25 slots and use No. 16 to 36 B.&S. gage single insulated copper 3 LE OE COIL SPAN N -·-·-·|-·|-}|{{{ 5 20 21 22 23 | 24 2 3 4 5 6 ← BRUSH Fig. 82. Armature Winding Diagram Elect Spec Armature Na……….. Frame No..........2 fole No Slots. No Coils..... 12 24 Na Commutator Bars ...4..... No Coils per Slot ........?.. No. Turns per Coil ........... Size of Conductor 14 DCC Coil Pitch Slots .............. Commutator Pitch......... 1192 Fig. 81. Armature Winding Tag 7 8 S wire for the windings. A double cotton (DCC) or a single cotton and enamel (SCE) insulation is used on sizes 16 to 28 wire, but double silk (DSC), single silk enamel (SSE), or enamel insulations are used on the 28 to 36 sizes of wire. The use of enamel insulated wire has 129 14 ARMATURE WINDING increased rapidly in the past few years and is giving as good satis- faction as double silk-covered wire. Insulating the Core. The burrs or fins on the armature punch- ings are very sharp and cut through the slot insulation easily, so after securing the electrical data and armature, all the sharp burrs or fins in the slots are removed as well as the sharp edges at the end of the slot. By giving close attention to this detail the number of grounded armatures will be reduced to a minimum. After re- moving all the burrs and the filings from the slots, one or two large fiber headers or washers are slipped over the shaft and pressed up against each side of the core. These headers are usually from 32 to inch thick. They are generally made with the same punch and die as the sheet-steel laminations and resemble an armature 16 DRIFT STICK HORN FIBER- HORN FIBER !!!! #HAPA www PEG TO HOLD INSULATION TIGHT WHILE WORKING ON NEXT SLOT LPAPER TUBE TO COMMUTATOR G III Fig. 84. Winding a Small Armature Fig. 83. Method of Insulating the Core 4 punching. The next operation is to place insulation in the slots. The continuous strip method shown in Fig. 83 is best adapted for this size of armature. A continuous strip of fish paper, horn fiber, or leatheroid about .010 of an inch thick and about to inch wider than the length of the armature core is used. Insert one end in a slot and hold it in place with a peg so that the insulation can be pulled tight. Crease the insulation over the edge of the slot and with a drift stick force the insulation into the next slot as shown in Fig. 83. The next peg is inserted in the slot, then the insulation is pulled tight and creased over the edge of the tooth. The remain- ing slots are insulated in like manner. The creasing of the insula- tion over the edges of the teeth will cause it to hold in place and to fit snugly against the sides of the slots. Leave the first pin in place 130 ARMATURE WINDING 15 until the insulating of the slots is completed. When the third slot has been insulated and a peg placed in it, the second peg can be removed and used in the fourth slot, and so on, only three pegs being needed. The first and last ends can be joined together outside the slot with shellac or some other sticking compound, although this may be dispensed with if the ends are flared like a funnel. Never use liquid glues for sticking the ends together, because most of these glues contain a small amount of acid which, in time, will corrode the copper wire. Where it is desired to use empire cloth or oiled muslin insulation in addition to the fish paper, the two strips can be fitted in the slots in the same manner as the first strip. The empire cloth, being the upper strip, is always placed next the wires. When it is desired to insulate between the top and bottom coils in a slot, the method described will work satisfactorily but smaller and correctly shaped pegs must be used. The first coil will always lie in the slot diago- nally and the shape of the peg should be such as to take care of this. Winding the Coils in Slots. This particular armature is for a 2-pole motor, with 12 slots and 12 coils, each coil having 20 turns. The coil pitch is slot 1 to slot 6. In order that it can be easily handled by the men, the wire for winding the armature is furnished on small spools weighing from 2 to 3 pounds. The end of the wire is fastened around the shaft beyond the commutator. As it is un- rolled from the spool it is passed through slot 1 to the back end of the armature, across to slot 6, then through to the front end, across to slot 1 and then through the slots again in the same manner as the first turn. The winder must watch carefully and see that the wires are arranged in the proper order, or rows, in the slots, Fig. 84, and that the different layers fit snugly. It is often impossible to arrange the layers uniformly across the bottom of the slot. In such cases where the armature has a fractional pitch winding, the wires can be built up in layers from the nearest corners of the two slots. When the required number of turns for that coil has been wound in the slots, the wire is looped back about 2 to 3 inches beyond the commutator. The loop to the commutator is given from three to five half-turn twists in order to hold the two wires close together and enable cotton sleeving to be easily slipped over them, providing addi- tional insulation when desired. The sleeving should extend to the 131 16 ARMATURE WINDING inside of slot. The next coil is wound in slots 12 and 5 in the same manner as the first coil. The first 5 coils wound on the armature will be located in the bottom of the slots, and a strip of empire cloth or fish paper is inserted in the slots above the wires in order to separate the top and bottom coils. This insulation can be inserted in the same manner as in the bottom of the slot, or a strip twice the width of the slot and bent in a U-shape can be slipped in the slot. The rest of the coils are wound in the same manner. The end of the lead from the last coil and the lead fastened around the shaft from the first coil are given several half turns to hold them together. The winding is next tested for grounds by connecting the terminals of a testing transformer to the copper wire and the core and applying the desired voltage. Where no testing transformer is available, the winding can be tested by connecting the proper number of lamps in the leads from the electric light or power circuit and attaching them to the winding and the core. The lamps are used to limit the current taken from the power circuit to a safe value, in case the windings are grounded. Without the lamps a short circuit would be placed on the power circuit. If the filament of the lamps becomes red it indicates that the winding is touching the core and the defective spot must be located and repaired. The defective coil can be located by cutting the loop on the end of the leads from the coil and testing between each coil and the core. The grounds are usually located at the ends of the slots and can often be repaired by inserting a piece of mica or leatheroid between the core and winding. If the winding is free from grounds, the slot insulation is trimmed and folded over the wires in the slot and a slot wedge, or fiber top stick, is driven in between the insulation and the tips of the teeth which extend over the slot. Connecting Winding to Commutator. There are two important facts which the armature winder must know before attempting to connect the coil leads to the commutator bars. The first thing to find out is whether the brushes are located on the center line of the poles, exactly midway between the center lines of adjacent poles, or in some other position. The majority of small motors has the brushes located either on the center line of the poles or midway between the center lines, but nearly all large generators and motors have the brushes located on the center line of the poles. There is 132 ARMATURE WINDING 17 usually provision made on the large generators and motors whereby the brushes can be adjusted to the correct position. This is not the case in railway, mine, vehicle, or small motors, and greater care must be used on these types in connecting the coils to the commutator bars in order to secure satisfactory service from these motors. The second important fact is whether the coils are con- nected for a lap winding or for a wave winding. The wave winding is used more than the lap winding on railway, mine, and vehicle motors and also on the small starting motors on gasoline automobiles. 12 In this particular armature there are 12 coils and 12 commu- tator bars with the brushes located under the center of the poles. Then locate the point on the core midway from the slot in which the coil is located and locate the commutator on the shaft so that BOTTOM LEAD 2 3 5 ENDING END BEGINNING END 10 11 12 2 3 45 Fig. 85. Diagram of Connections to Commutator the mica between the bars will be on this center line. Call the bar to the left of the center line 1 and the one to the right 2, as in Fig. 85. Now connect the bottom lead, or beginning end, of the coil in the bottom of slot 1 to bar 1 and the ending end of that coil to com- mutator bar 2. The beginning end of the bottom coil in slot 2 is also connected to bar 2. This operation is repeated for all leads until they are connected to the commutator. In winding this armature the ending lead of the first coil and the beginning lead of the second coil are twisted together so these two leads can be con- sidered as one connection to be attached to the commutator bars. It is very important that the coils are connected in the proper order to the commutator bars or the motor will heat up very rapidly and there will be considerable sparking at the commutator. In Fig. 85 the coil has a pitch of 1-7 while in Fig. 84 the pitch is 1-6 which is a 133 18 ARMATURE WINDING fractional pitch winding. These armatures are used on a 2-pole machine. Testing Armature Windings. The next step after connecting the lead to the commutator is to test the windings for short circuits, open circuits, and grounded or reversed coils. Bar-to-Bar Test. The bar-to-bar test is a rapid and sure method of locating these defects. The method of making the test is the same for any armature, no matter whether it is a ring-wound armature or a drum-wound with lap or wave windings. A source of direct current is connected to two points on the commutator as shown in Fig. 86. The direct current can best be obtained from the RHEOSTAT سم || 10 12 9 a TO D. C. LINE +1 |- 10 12 8 11/2 7 6 2 3 4 5 3 4 5 MILLIVOLTMETER + Fig. 86. Diagram of Connections for Testing Winding 115-volt lighting circuit, although where this is not available a number of 6-volt or 12-volt batteries may be connected in series to give the required current. A rheostat is inserted in the circuit in order to regulate the amount of current passing through the armature and thus prevent overheating of the windings. The two leads from a direct-current millivoltmeter are touched to two adjacent commu- tator bars and the current adjusted until a quarter to a half of a full scale reading is obtained on the meter. The millivoltmeter leads. are then touched to bars 7 and 8, 8 and 9, etc., all around the com- mutator, and if about the same readings are obtained from adjacent bars the winding is connected properly. If there is only a very C 134 ARMATURE WINDING 19 small deflection on the meter or none at all when the leads are con- nected to bars 9 and 10, it indicates that coil 10 is short-circuited. If no deflection is obtained on the meter, the short circuit may be due to copper chips or dust forming a path over the mica insulation. When the test is made after the leads are soldered to the commutator bars, the short circuit will nearly always be due to the solder flowing over the mica to the adjacent bar. This solder can be filed or scraped off. When the millivoltmeter leads are touched to bars 11 and 12 and to 12 and 1 and there is no deflection of the pointer of the meter, but when the leads are touched to bars 1 and 2 the pointer is thrown violently off the end of the scale, either an open circuit in the coil connected between these two bars has occurred or a wrong connection of the leads to the bars has been made. The defect can be deter- mined by bridging the mica between bars 1 and 2 with a short piece of copper wire and noticing whether a spark is obtained when the wire is removed. The obtaining of a spark will indicate that there is an open circuit in the coil. Another method of determining whether the defect is an open or reversed coil is to reduce the current through the armature until the drop between bars 11 and 5 can be read on the millivoltmeter and then touch the leads to bars 1 and 2. If the drop across these two bars is the same as from bar 11 to 5 the open circuit is in this coil, but if the drop is only to of the reading across bars 11 to 5 it would indicate reversed coils. It is sometimes possible to locate the open circuit, especially if it is in the leads, by attaching the millivoltmeter to bars 1 and 2 and ham- mering and pressing the armature leads and the winding with the hands. In Fig. 86 the defect is at b. When the open circuit is in the body of the coil, it is usually necessary to remove the coil and rewind it. After this defect in armature coil 2 has been repaired, the remaining coils can then be tested. If, when the millivoltmeter leads are touched to bars 12 and 1, only half the usual deflection is obtained, it is indicated that either half the turns in the coil are short-circuited or only half the correct number of turns are wound in this coil. Should this number of turns be omitted, it may be easily detected by looking at the coil. If only a few turns are omitted or shorted, as indicated by the meter reading, it is necessary to use other tests to locate the defect. 1 10 135 20 ARMATURE WINDING If the deflection of the millivoltmeter needle is very much greater when connected to bars 2 and 3 than when connected to other bars, it indicates that there is a very poor connection between the coil and commutator bars, wrong connection of the coil leads to the commutator bars, a greater number of turns placed in that coil, or a smaller size of wire used. In this case the millivoltmeter de- flection is exactly twice the usual reading, indicating that the leads of the coils to bar 2 or bar 3 have been interchanged. Connecting the millivoltmeter leads to bars 3 and 4 gives a reversed reading which shows that these are the reversed leads. It will be found in testing armatures which have the wire wound directly in the slot, Fig. 84, that the millivoltmeter reading will not be the same for all bars. This is because more wire is used in winding the last coil, which is wound on top of the other coils. The millivoltmeter reading will be lowest for the first coil and greatest for the last. This condition will be most noticeable on armatures wound with a large number of turns or when fine wire has been used. There should be a gradual increase or decrease in the readings for the different bars except that there will be a big change between the readings for the bars connected to the first and the last coils. If not kept in mind this change may easily cause one to believe that there is a defect in the coil. A similar variation is sometimes obtained on large armatures when other than an even number of turns per coil is used. Frequently, such windings as 11, 13, or 13 turns per coil are specified by the designer. In the case of 1½ turns per coil, one coil will have 2 turns, the next coil 1 turn, the next 2 turns, etc., and one millivoltmeter reading will be high, the next one low, the next one high, etc. When 11 turns per coil are used, the number of turns per coil will be 2, 1, 1, 2, 1, 1, 2, 1, 1, etc. For 13 turns per coil the order will be 2, 1, 2, 2, 1, 2, 2, 1, 2, etc., and the readings will be high for the 2-turn and low for the 1-turn coils. Testing for Grounds. The armature winding is tested for grounds by connecting one terminal of a testing transformer to the commutator and the other terminal to the end of the shaft or core and supplying the desired alternating current voltage for one min- ute. There is a small fuse or circuit breaker in the primary or low voltage side of the transformer which. in case the insulation is 136 ARMATURE WINDING 21 defective, will blow or the circuit breaker will open. Often the location of the defect or ground may be located by observing a spark or smoke which occurs at the defective spot when the circuit breaker opens. The location of the ground may also be located by use of the apparatus shown in Fig. 86, except that one brush is connected to the shaft and the other one to the commutator. One of the millivoltmeter leads is connected to the shaft and the other lead is touched to the different commutator bars until the bar is found which gives the lowest reading, or no reading at all.. Dielectric Test. The voltage to be used in testing the insula- tion on the armatures is that recommended in the Standardization Rules of the American Institute of Electrical Engineers in section 500 which is as follows: The standard test for all classes of apparatus, except as other- wise specified, shall be twice the normal voltage of the circuit to which the apparatus is connected, plus 1000 volts, applied for one minute. One exception to the above rule is for motors of less than one- half horsepower which are used on household appliances, such as washing machines, vacuum cleaners, etc., on which a test voltage of 900 is applied for one minute. It is customary to use a slightly higher voltage on the test in the factory in order to insure that it will not fail on final test. In case a higher voltage is used, it is not necessary to apply the test for one minute. The test voltages recommended for shop use for different kinds of motors and generators operating at various volt- ages is given in Table I. Most testing transformers are provided with steps of 250 volts each. If the transformer is not provided with a tap for that particular voltage, use the next higher voltage. Testing for Short Circuits. The best way to locate short- circuited coils in an armature is by the use of a small transformer, frequently called a "bug" or "growler." The growler is placed on the armature core over the coils and an alternating current passed through its windings. It will then act as a transformer and gen- erate a voltage in the winding of the armature. If the insulation of the coils be perfect, no current can flow through the armature windings, which then become the secondary of the transformer. Should one or more turns of the armature coil be short-circuited, 137 22 ARMATURE WINDING RATED VOLTAGE 25 0 to 26 to 150 151 to 300 301 to 500 501 to 650 651 to 1000 TABLE I 60 Seconds 1000 1250 1500 2000 2250 2500 Test Voltage 2 Seconds 1250 1500 2000 2250 2500 3000 a heavy current will flow through that part of the winding causing the defective coil to heat up. The defective coil may be located by passing a piece of sheet metal around over the various armature coils and where there is a short-circuited turn in the coil it will cause the sheet metal to vibrate or be attracted when it is over the slot containing the defective winding. This outfit is a great help in testing the windings after the leads have been soldered to the commutator, because if there is sufficient current induced in the armature winding it will often melt the solder that extends across from one commutator bar to the other and remove the defect from the armature. If it is desired to see the effect of a short- circuited coil, the two commutator bars can be short-circuited with a screw driver or a short piece of wire and the same result will be obtained as when there is a short-circuited coil. It is pos- sible with this apparatus to locate or detect one short-circuited turn in an armature coil. Constructing Growler. The construction of such a device for use on an armature having a diameter of about 4 inches is shown in Fig. 87. This device is usually constructed by using a pole piece from the motor having an armature of corresponding size and cut- ting a slot about halfway through from the inner diameter of the pole piece. This will leave a core about an inch thick and the full length of the armature or pole piece. Several layers of empire cloth or linotape are wound around the core and the sides are insulated with pieces of horn or rawhide fiber about of an inch thick. Generally the groove is wound with as many turns as possible of No. 10 B.&S. gage, double cotton-covered magnet wire. This will enable the growler to be operated from a 110-volt alternating- current light circuit. 6 138 ARMATURE WINDING 23 By experimenting, a size of winding can be designed that will produce a voltage from two to three times as great between com- mutator bars as that which actually occurs in practice. This has an advantage in that the coils are subjected to a higher voltage than actually occurs in practice. The higher voltage will cause any slight defects which are likely to develop to be indicated at this time. A growler of larger size can be constructed to take care of the larger armatures and, by using two or three different sizes, it is HORN FIBER RIVETS- о *O -2/" O K~~~ 1 ½” — —✈ WIND THIS SPACE WITH HORN FIBER RADIUS ABOUT 2 Fig. 87. Small Testing "Bug" or "Growler" possible to take care of the complete range from a motor of small size to a 20- or 30-horsepower motor. In the larger growlers a smaller number of turns is used but the wire is of larger size. The construction of another type of growler is shown in Fig. 88. It is used very extensively for small armatures because it can be set on a bench and the armature placed on top of it. In building this growler the laminations, which are 5 by 6 inches, are assembled and held in place by clamps while the bolt holes are being drilled. After bolting the laminations together, the block thus formed can be placed in a milling machine or a shaper and the slots for the coil cut out. When such machines are not available, the two sides of each slot may be cut with a hack saw and, by removing the bolts, the bottom of the slot can be cut out with a sharp cold chisel, using the irst one of the laminations for a template or guide. The lamina- 139 24 ARMATURE WINDING tions can then be reassembled and held together by 1-inch bolts which are insulated from the laminations by paper bushings and washers. The burrs are then removed from the inside of the slot with a file, and the laminations shaped to the desired radius. The core of the growler should be insulated with a fiber sleeve to protect the winding from the core. When the growler is to be used on a 110-volt, 60-cycle circuit, it should be wound with 150 turns of No. 10 B.&S. gage square double cotton-covered magnet wire. For a 220-volt, 60-cycle circuit, 300 turns of No. 13 wire is used; and for a 110-volt, 25-cycle circuit, 350 turns of No. 14 wire is used. After each layer is wound, it should be painted with an insulating varnish, 60100 3100 NIL DRILL k-/". RAD DIG · 21½" 5" 0.074 LAMINATION |----3-- pa me vdekje Fig. 88. HI-Type "Growler" PUSH SWITCH 學分 ​"BRASS END PLATE such as bakelite, and then baked in an oven the same as the arma- ture coils. A snap or push switch should be placed in the connecting cord to shut off the current when shifting the armature or growler. The current should be turned on only when there is an armature across the core, because it takes three to five times as much current without an armature as with one. Other Uses of Growler. The growler can also be used for locat- ing reversed leads to the commutator and open coils by connecting a telephone receiver to two or three adjacent commutator bars and slowly revolving the armature, meanwhile keeping the testing leads in the same position with relation to the growler. A change in the tone of the telephone receiver will indicate a defective coil. When- ever it is possible, the contacts for the leads to the telephone receiver should be supported on a fixed arm so that their position will not change while testing the armature. 140 ARMATURE WINDING 25 WINDING A MEDIUM-SIZED ARMATURE Standard Ratings. The general method of procedure in wind- ing a medium-sized armature is similar to that described for a small armature in the preceding pages. The details are, however, entirely different. Each coil of a medium-sized armature is wound with the desired number of turns and is insulated before being placed in the slots of the armature. The diamond type of coil is used almost entirely. The output of a medium-sized armature is from 1 to 50 horse- power at a voltage of from 60 to 600 volts. The standard voltages for direct-current generators are 125, 250, and 600, while the standard voltage ratings for motors are 115, 230, and 550 volts. The generator voltage is about 10 per cent higher than the motor voltage because the circuits are usually designed for a 10 per cent voltage drop between the generator and the motor. Insulating Coils. The coils are usually wound in the form of a hairpin loop, as shown at A in Fig. 72, and then spread to the de- Fig. 89. Formed-Wound Coils Ready to be Taped Courtesy of the Reliance Electric and Engineering Company sired shape by means of the machine shown in Fig. 77. The coils are frequently wound on a former to give the desired shape, Fig. 89. It will be noted that these coils are composed of four turns of two cotton-covered wires wound side by side. The two wires of each read can be connected to the same commutator bars and thus 141 26 ARMATURE WINDING connect the two wires in parallel with each other, or each wire may be considered a separate coil and connected to different commutator bars. The two wires will be connected in parallel when the number of commutator bars, slots, and coils on the armature are the same, and there will be two coils in each bundle or slot when there are twice as many bars on the commutator as there are slots in the core of the armature. In Fig. 89 it will be seen that there are four bands used to hold the wires in place until the coil is taped. These bands are made from sheet lead about of an inch thick and can be easily attached or removed from the coil when desired. The coils, after Fig. 90. Taping Coils by Hand Courtesy of the Reliance Electric and Engineering Company being formed to the desired shape, are heated in an oven and, while hot, dipped in a tank containing amber-colored baking insulating varnish. They are then placed in an oven heated to about 100 degrees centigrade (212 degrees F.) and allowed to bake until dry. When dipping the coils, care must be taken not to permit the ends of the leads to enter the compound because it is very difficult to remove this insulation when connecting the leads to the commutator and it also makes it difficult to solder the leads to the commutator. In Fig. 89 the light-colored tips of the leads have not been dipped in the varnish, while the dark portion of the leads and coil have been. The insulating varnish penetrates the cotton covering on the wire and binds the wires together so that they cannot easily shift their position. 142 ARMATURE WINDING 27 Taping Coils. Cotton sleeving is slipped over the two wires forming the leads, as shown in Fig. 90, and the whole coil is taped with half overlapping cotton tape. The sleeving should extend into the coil about inch from where the leads leave the coil, and 2 or 3 turns of the tape should be taken around the sleeving at this point in order to fasten it securely to the coil. In Fig. 90 the opera- tor is winding the tape on the coil so that half the tape is lapped over the preceding turn, thus placing two thicknesses of cotton tape on the coil. It is necessary that the tape be stretched very tightly when taping the coils in order to produce a solid dense coil P Fig. 91. Taping Coils with a Machine Courtesy of the Reliance Electric and Engineering Company free from air pockets. The machine shown in Fig. 91 winds the tape on with a higher and more uniform tension than can be obtained by hand. The taped coil is then heated in an oven for half an hour and, while hot,, is dipped in amber-colored baking varnish as shown in Fig. 92 and allowed to remain for a few minutes. It is then placed in the oven with a temperature maintained at 200 to 220 degrees Fahrenheit until the coil is baked dry. This treatment is repeated two or more times until a glossy varnished surface is obtained on the coil. The coil is now ready for use on a 125-volt 143 28 ARMATURE WINDING Fig. 92. Dipping Coils in Insulating Compound Courtesy of the Reliance Electric and Engineering Company Fig. 93. Taping Field Coils Courtesy of the Reliance Electric and Engineering Company 144 ARMATURE WINDING 29 machine. For a 250-volt machine the whole bundle or coil is taped again with cotton tape, not overlapping, but for a 600-volt machine the cotton tape is half overlapped and the dipping and baking process is repeated again until a glossy surface is obtained. On 600-volt work a layer of half-overlapped linotape or empire cloth is often used under the first layer of cotton tape. The field coils of the motor are often dipped and baked in a manner similar to the armature coils, then taped as shown in Fig. 93, and given another dipping and baking after they are taped. Insulating the Core. It is important to see that all the sharp burrs or fins on the laminations are removed with a file before beginning to insulate the core. One small steel sliver or burr can very easily cut through the insulation and ground the coil. This may cause the armature to burn out when placed in service. A Fig. 94. Small Armature Core Ready for Winding Courtesy of the Reliance Electric and Engineering Company view of a core ready for winding is shown in Fig. 94. There is a supporting ring on the left-hand end plate of the core which should be insulated with wood, fiber, or tape. The diameter of this ring should be nearly the same as the bottom of the slots so the back end of the coil will extend out straight and rest on this ring. It is often necessary to build this ring up to the correct diameter with strips of fiber before binding them to the ring with tape. The method of performing this work is shown in Fig. 95. After insulating the supporting ring the next operation is to insert the U-shaped slot insulation in all the slots, Fig. 96. The treated coils shown in Fig. 92 are used in winding the armature and, if they have been spread to the correct shape and pitch, they can be easily inserted in the slots. A paraffin-coated fish paper is often used as the slot insulation. This allows the coil to enter the slot 145 30 ARMATURE WINDING Fig. 95. Insulating the Supporting Ring at the Back End of the Armature Courtesy of the Reliance Electric and Engineering Company Fig. 96. Placing Coils in the Slots of the Armature Core Courtesy of the Reliance Electric and Engineering Company 146 ARMATURE WINDING 31 much easier than the ordinary fiber paper does. When paraffined paper is not used in the slots, the portion of the coil that enters the slot should be treated by rubbing the coil with a bar of paraffin. This will enable the coil to enter the slot much easier and is well worth the time spent in doing the work, especially when the coils are a very tight fit. It is also necessary to insert strips of fiber between the top and bottom sides of the coils on both the front and back ends of the winding which is outside the slots. These fiber strips are to prevent the top coil from pressing against and becom- ing short-circuited with the lower coils, due to the pressure from the banding wires which are above these points on the winding. Winding the Armature. The coil is inserted in the slot so that one side will be in the bottom of the slot and the other side in the top of another slot. After inserting the first coil its span should be checked with the electrical data for that particular armature, be- cause it frequently happens that the coils may have been spread for a different span than that called for and the error would not be discovered until the completed machine was placed on test. The next coil is inserted either to the right or the left of the slot in which the bottom side of the first coil was placed. This coil will always be placed so that the center of it will be over or above the first coil. The coils are all inserted in this manner until the winding is com- pleted. It will be necessary to raise up out of the slot all the top coils that have not been placed on top of the bottom coils so that the bottom sides of the last coils can be inserted in the slots. It may be necessary to use a wooden or, better still, a rawhide mallet to drive the coils down in the slots. When a mallet is not avail- able, a strip of hard fiber to inch thick and about 2 inches wide can be held on the coil while a hammer is used on the fiber to drive the coil into place. This will allow the coils to be driven into place without smashing or cutting the insulation. The slot insulation is folded over the top of the coils and any excess length is cut off, so that the slot wedge, or top stick, can be driven in under the teeth of the slot. The leads of all the coils should be connected together with a piece of fine, bare copper wire and the winding given the usual dielectric test in order to locate any defects or grounds which may exist in it. The top leads from the coils are all bent back so that they will point toward the pulley end of the 147 32 ARMATURE WINDING Fig. 97. Placing Upper Layer of Connections to the Commutator in Position Courtesy of the Reliance Electric and Engineering Company Fig. 98. Placing Insulation over the Lower Leads to the Commutator Courtesy of the Reliance Electric and Engineering Company 148 ARMATURE WINDING 33 shaft, and the bottom leads are pulled outward in an inverted cone shape to enable the commutator to be pressed into position on the shaft. Connecting the Coils. The correct commutator bar to which the bottom lead of the coil is connected is located from the data as explained and illustrated in the preceding pages. The bottom leads of adjacent coils are connected to adjacent commutator bars until the bottom leads have been connected to all the bars. The lower leads are insulated from each other near the commutator by a cotton tape, about an inch wide, that is passed over one lead, under the next lead, over the next lead, etc., as is also done on the top leads, Fig. 97. This tape is shown lying loosely on the top leads that have been bent back over the core. A piece of heavy canvas is placed over the lower leads, Fig. 98, after they have been connected to the commutator bars. The canvas is secured in place with friction tape, which is represented by the black bands in Fig. 97. The winder is now ready to connect the top leads or end con- nections to the commutator bars. A pair of test leads, with a lamp in series with one or both leads which are connected to the electric light circuit, is needed in order to find the two ends of the same coil. After locating the correct bar and connecting the first of the top leads to it, the lead for the adjacent coil is located with the test lamps and connected to the next commutator bar. This process is repeated until all the leads have been connected to the com- mutator. The excess part of the wires that extend through the tang or riser of the commutator bars is cut off, either with a wire cutter or chisel, so that a heavy soldering iron can be held up against the end of the wires or risers in order to heat them for soldering. In soldering the leads a half tin and half lead solder is used with solution of rosin in alcohol for a flux. In this operation care must be taken that the solder does not run down the back side of the commutator and bridge across from one bar to the next, causing that coil to be short-circuited. When soldering, it is a good plan to place the armature so that the front of the commutator will be much lower than the back. The solder will then run away from the back side of the commutator. Dipping the Armature. The completed armature should be placed in the oven for from one to two hours in order to dry out 149 34 ARMATURE WINDING all moisture and, while hot, dipped in an insulating compound, Fig. 99. Care must be taken with large armatures when attaching the clamp to the shaft to prevent the shaft from becoming dented at the portion which fits in the bearing. In order to avoid this trouble a split steel sleeve, having an inside diameter the same as the shaft, should be provided and placed inside the clamp, so that the pressure from the clamp will be over a considerable area. The bearing portion of the shaft is finished to within a half thousandth Fig. 99. Dipping Completed Winding in Insulating Compound Courtesy of the Reliance Electric and Engineering Company of an inch (0.0005 inch), and any nicks or flat spots will cause the hearings to overheat. Banding the Armature. A band of high-grade steel piano wire is wound on a strip of leatheroid that is placed around the arma- ture and over the coils about half an inch to two inches from the edge of the core in order to prevent centrifugal force from throwing the coils outward when running at high speed. This is done either before or after the armature has been dipped and baked. It is best to do this work while the armature windings are hot, because the insulation shrinks when heated, is more flexible, and can be pulled down tightly much easier than when cold. When the first wire of the band is wound on the armature, small tin clips should 150 ARMATURE WINDING 35 TEETH be inserted under the wire; and when the required number of turns has been wound on the armature, the ends of these clips can be turned up over the wires in order to hold them tightly side by side. These clips are soldered over with a tin solder and a thin coat of solder is run over the whole band to hold the wires together. The completed armature is then placed in a lathe and a very light cut is taken over the face and side of the tang or riser of the commutator to make it perfectly true. If a commutator is eccen- tric even five thousandths of an inch (0.005 inch), it will push the brushes away from the commutator this much when the machine SLOT END FLANGE CLAMPING BOLTS SPIDER HUB COMMUTATOR KEY Fig. 100. Rotor Assembly for a 6-Volt 7500-Ampere Generator Courtesy of The Ideal Electric and Mfg. Co., Mansfield, Ohio is running. Instead of being conducted from the commutator to the brush the current must pass through this much of a gap, which will cause a slight arc and sparking. This will cause the commutator to operate at a higher temperature than otherwise. WINDING A LOW-VOLTAGE ARMATURE The winding of a low-voltage generator which is used for battery charging and electroplating is very similar to that of a medium-sized armature. The main difference is that in winding the low-voltage armatures fewer turns of wire are made per coil, and the size of wire used in the windings is larger. Often, in order to obtain the required cross-sectional area of the conductor, several wires are connected in 151 36 ARMATURE WINDING parallel. In larger armatures, small copper bars bent to shape and insulated with tape are used for the coils. On low-voltage generators used in electroplating work, the rotor core is usually much shorter in length and has a larger number of slots than the 125 or 250-volt machines. The slots are usually narrow and very deep as shown in Fig. 100. The laminations are assembled on the spider and keyed to it, then they are clamped tightly together by bolts that pass through the end flanges and rotor spider. The rotor spider is pressed on the shaft and secured to the hub by a key. SLOT WEDGES SLOT INSULATION COIL INSULATION COIL ENDS COIL LEADS Fig. 101. Insertion of Armature Coils in Slots Has Been Completed Courtesy of The Ideal Electric and Mfg. Co., Mansfield, Ohio The particular rotor in Fig. 100 is used on a 6-volt generator that will produce 7500 amperes of current for use in electroplating work. The armature coils are of the involute type and pressed to shape in a forming die or jig. The coils are insulated with linen tape, then dipped in insulating varnish and baked dry. Each slot is insulated with horn fiber and paper insulation, Fig. 101, before the coil is inserted. After the coil is put in place, the paper insulation is folded over and a hard fiber top stick or wedge is driven into the keyway or groove in the top of the slot. These wedges hold the coils in place. The operation of inserting the coils and wedges in the slots has been completed in Fig. 101. There are two sets of windings, and a commutator is to be placed on each end of the armature in Fig. 101. Each coil in this particular 152 ARMATURE WINDING 37 RISER SLOT armature consists of three square wires, probably some size between No. 10 and No. 6, connected in parallel. There are two coil sides (one side of each of two coils) placed in each slot. The coils in the odd- numbered slots are connected to one commutator and the coils in the even-numbered slots, to the other commutator. There are about 126 slots in the core and 126 armature coils. One of the assembled commutators, Fig. 102, for the above armature contains 63 bars and 63 risers. In large machines equalizers EQUALIZERS COMMUTATOR CLAMPING BOLTS RISERS COMMUTATOR BARS MICA Fig. 102. Commutator Assembly Ready for Test on Dynamic Balancing Machine Courtesy of The Ideal Electric and Mfg. Co., Mansfield, Ohio are used to join together commutator bars that have the same voltage. The number of commutator bars joined together is the same as the number of pairs of poles or the number of sets of positive brushes. The armature shown in Fig. 101 is for a 14-pole machine (7 pairs) which will have 7 sets of positive brushes. The number of commutator bars in Fig. 102 from one positive brush to the next is (637) 9. Therefore, every ninth commutator bar is joined together. Thus bars 1, 10, 19, 28, 37, 46, and 55 are joined together and form one equalizer ring. Then bars 2, 11, 20, 29, 38, 47, and 56 are joined together and form the second equalizer ring. There are as many equalizer rings as there are commutator bars between positive sets of brushes. The purpose of these rings is to 153 38 ARMATURE WINDING equalize any slight difference in voltage produced by one set of armature conductors under one pair of poles as compared to those under some of the other sets of poles, since it is impossible to have all magnetic fields of the same exact magnetic strength. The current flows through these equalizer rings instead of flowing from one com- BOTTOM COIL LEADS EQUALIZERS TOP COIL LEADS SPACER WEDGES Fig. 103. Connecting Coils to Commutator Courtesy of The Ideal Electric and Mfg. Co., Mansfield, Ohio mutator bar through the positive brush to the brush holder frame and then to another positive brush and commutator bar. The re- sistance of the parallel path through the brushes is many times that through the equalizer ring, and so these equalizers reduce unnecessary heating of the commutator bars and brushes, thus improving the operation of the generator. The assembled commutators are fastened to the shaft with a key. The ends of the armature coils in the bottom of the slots are bent to secure the proper "throw" and then connected to the bottom of the groove in the riser as shown in the top part of Fig. 103. All the bottom coil leads are bent in the same manner and connected to the risers. Then the top coil leads are bent in the opposite direction from that of the bottom leads and connected to the top of the groove in the riser. The connections of the coil leads to the risers have been completed for the right-hand commutator in Fig. 103. A wood or fiber spacer wedge is inserted between the commutator 154 ARMATURE WINDING 39 risers in order to hold the sides of the riser slot tightly against the coil leads when they are being soldered. After the soldering work is completed, the wedges are removed. The next operation on the armature is to put the band wires in place, then the armature windings and risers are painted with a BAND WIRES BALANCING WEIGHT RISERS EQUALIZERS Fig. 104. Completed Armature Ready for Test on Dynamic Balancing Machine Courtesy of The Ideal Electric and Mfg. Co., Mansfield, Ohio good air-drying insulating varnish. The completed armature is next placed on a dynamic balancing machine, Fig. 104, where it is run at speeds up to 1/2 times the normal operating speed. Any tendency to vibrate due to more weight on one side of the shaft than on the other is corrected by adding more weight, usually solder on the band wires, to the lighter side. 155 CONNECTING COIL LEADS TO COMMUTATOR RISERS Courtesy of Carnegie-Illinois Steel Corporation, Pittsburgh, Pa. DIRECT-CURRENT REPAIRING MOTORS AND GENERATORS REPAIRING MECHANICAL PARTS Locating Defects. The general nature of the defect in a motor or generator is usually determined before the motor is sent to the repair shop, or repair department. In those cases where the nature of the defect is not known to the repair shop or to the one doing the work, the motor should be connected to a source of supply the same as that given on the nameplate. In many cases the name- plate will be missing, and therefore the only thing to do is to connect it to the lowest voltage circuit available. The usual voltages for motors used for industrial power work is 110 to 220. When the size of the motor is such that the output may be two horsepower or less, it may be used either on 110 or 220 volts; while if the motor is larger, it undoubtedly will be operated on 220 volts. The field winding of industrial power motors is either shunt or compound, except crane, hoisting, mining, and railway motors, which are nearly always series motors. Motors that are used on this class of service. can be easily identified by their appearance. When testing out the motor a small fuse should be placed in the line circuit, and when possible a continuous duty rheostat, with sufficient resistance to limit the starting current to a safe value, should be inserted in series with the armature. This resistance can be decreased as the motor speeds up until it is running at normal speed. With the motor running at normal speed it should be examined for sparking at the commutator, for end thrust against either one of the bearings, and for lubrication of the bearings by the oil rings. When there is sparking at the commutator, the defect can be located by using the methods given in section on "Locating Motor and Generator Troubles." The end thrust against one of the bearing sleeves can be located by using a pointed stick to push the armature endwise in the bearings. It should be possible to push the armature endwise fromto of an inch at each end. If it is impossible to push 8 157 2 DIRECT-CURRENT MOTORS AND GENERATORS the armature endwise in its bearings while it is running, the arma- ture is pushing against the bearing on the opposite end. This end thrust is due to the fact that the center of the armature core is not in line with center of the pole pieces. Where this thrust is excessive, it may be due to the fact that the pulley end of the machine was placed on the wrong side of the frame. This condition can easily occur when the poles are located near the center of the frame and the brush holders are supported from the bearing bracket. This can be remedied by removing the armature and bearing brackets and turning the frame end for end, or by removing the pole pieces, when they are bolted against the frame, and turning them end for end. Tearing Down the Machine. It is always best to mark the parts that fit on one another before removing them from the machine. The brush rocker arm is usually fastened in place on motors or generators that have interpoles so that it cannot be shifted from its correct position. If it should be necessary to remove the brush rocker arm, its location should be marked by means of a center punch or small narrow chisel so that it can be replaced in the same position as originally. When the brush rocker arm is supported from the bearing bracket, it is seldom necessary to remove it in taking the machine apart. It is nearly always necessary to remove the brush yoke when it is supported from the frame and before removing it a chisel mark should be made on the frame and one directly opposite it on the brush yoke. In removing field coils and pole pieces the numbers 1, 2, 3, and 4, should be stamped on the commutator side of the pole and also on that edge of the frame in order that they may be returned to the proper place when reassembling the machine. The reason for this is because sometimes the manufacturers do not make the poles symmetrical or, in order to make the machine meet certain require- ments, one side of the pole tips may be cut off or made to have a greater air gap on one side than on the other. It is also necessary to watch and see that any shims or thin pieces of sheet steel that are between the pole and frame are securely attached to the pole in order to prevent them from being lost. The cap screws that are used to hold the pole pieces to the frame should be inserted in the tapped hole in the pole and they should be examined to see if they will fit properly. A half-inch cap screw with 13 threads per inch 158 DIRECT-CURRENT MOTORS AND GENERATORS 3 is used on a large number of machines of medium size for holding the pole pieces in position, and often a mistake may be made and a cap screw with 12 threads per inch will be used which will give trouble, because it will not fit properly. The hole in the pole piece may not be drilled deep enough or threaded clear to the bottom, and this will not allow the cap screw to enter far enough to hold the pole firmly against the frame, although the cap screw has been tightened as tight as the rest with a large wrench. If this condition is not remedied before the motor is connected to the line, there will be trouble due to the pole piece being attracted toward the armature and possibly coming in contact with it while it was running, which would wreck the machine. Worn Sleeve Bearings. A worn bearing can be discovered by taking hold of the end of the shaft and lifting it vertically and side- ways and noting if there is any play between the shaft and bearing. The bearing on the pulley end of a motor or generator usually wears more than the one on the front or commutator end of the machine. The action of the shaft and belt on the pulley is similar to a lever. The force on the bearing on the pulley end multiplied by the distance from its center to the center line of the belt must equal the force on the bearing on the commutator end times the distance from the center of its bearing to the center line of the belt. The distance from the bearing on the commutator end to the belt is several times the distance the other bearing is from the belt; therefore the force on the pulley end bearing must be several times that on the other bearing. Removing Sleeve Bearings. It is necessary to use care when attempting to remove the bearings from the bearing bracket, other- wise the bracket will be damaged so badly that it will be necessary to replace it. Each manufacturer almost invariably uses a different method of preventing the bearing sleeve from turning in the bracket and for retaining the oil ring in its proper place. In Fig. 1 the bearing sleeve A is pressed up against the shoulder of the bearing bracket at B and the set screw P prevents the sleeve from working loose in the bracket and revolving with the shaft. It is necessary to remove this set screw before attempting to remove the bearing from the bracket; otherwise the set screw P will be broken or, as is usually the case, the part of the hub of the bearing bracket shown 159 4 DIRECT-CURRENT MOTORS AND GENERATORS at X will be broken off. The bearing bracket is usually made of cast iron, and it is impossible to repair it, thus making it necessary to secure a new one from the manufacturer. On some machines there is a slot milled in the bearing sleeve from the set screw P to the right hand of the sleeve. In this case the set screw will have B G X. P. BUCCOONE --A— E £100000 O Fig. 1. Method of Locking Bearing in the Bracket one end milled off, as shown in the upper right corner of Fig. 1. The thickness of the flat portion of the set screw E will be about 64 a ¿ of an inch less than the slot. With this type of locking device it is impossible to insert or remove the set screw while the bearing is in place. Another method of holding the bearing in place is by the use of a small key, as shown in Fig. 1 at C. In Fig. 2 a lug is cast on the bearing sleeve which, when forced into position in the bearing bracket, is located between two lugs cast on the hub of the bracket. The disadvantage of this type of bearing sleeve is that a special pattern must be used and it is harder to obtain as good castings and bearings as when the sleeve is made from a hollow cylinder, Fig. 1. When the diameter of the shaft exceeds two or three inches, a babbitted 160 DIRECT-CURRENT MOTORS AND GENERATORS 5 bearing is often used. There is usually a cast or malleable iron sleeve used to transmit the strain from the babbitt metal to the bearing bracket and also act as the outside of the mold when the molten babbitt metal is being poured into place. A lug may be cast on the iron sleeve to prevent the bearing from turning, or a three-eighths Fig. 2. A Phosphor Bronze Bearing Courtesy of the Louis Allis Company of an inch hole can be drilled nearly through the iron sleeve and a short steel driven into this hole. It is also necessary to see that the oil ring is moved so that it will not interfere with the bearing sleeve when it is being removed. The bearing bracket shown in Fig. 1 should be turned upside down so that the oil ring will drop into the cavity or groove D while the sleeve is being removed. If this precaution is not taken and the oil ring is left in the position shown, the sides of the ring will catch on the edges of the hub at G, thus damaging itself and also the bearing. The oil ring is often retained in the slot by means of a wire that is run through a small hole which is drilled through the upper part of the sleeve and parallel to the center line of the shaft. Another method sometimes used is to attach a small metal clip to the top of the sleeve with a small screw after the bearing is in place. This clip is inserted through the top oil cover F in Fig. 1 and when in place will extend over the top of the oil ring groove and keep the oil ring in place. Replacing Sleeve Bearings. When placing new bearing sleeves in the bearing bracket care should be taken to see that any slots, lugs, and keyways are in line with the proper set screws and grooves 161 6 DIRECT-CURRENT MOTORS AND GENERATORS before starting to press them in place. The outside diameter of the sleeve is usually from one to five thousandths of an inch larger than the hole in the hub so they will be a light press fit. When possible the bearings should be pushed into place with a small hand press or by a heavy lever. When these methods cannot be used and it is necessary to drive the bearing into place with a hammer, a short length of round brass or copper bar the same size as the largest diameter of the sleeve should be held against the sleeve. The hammer should be used on the end of the bar in order to prevent marring or damaging the end of the bearing sleeve. Assembling Ball Bearings. The use of ball bearings on electric motors and generators is becoming greater each year due to the fact OUTER CAP -FELT BEARING BRACKET INNER END CAP. INNER- BALL BEARING RACE 5 BEARING BRACKET Fig. 3. Method of Mounting Ball Bearings ANNIN OUTER END CAP LOCKING DEVICE OUTER BALL BEARING RACE that they will operate for long periods of time without attention. This does not mean that they will operate forever without any attention, but where the motor having sleeve bearings has to be given attention once a week, the motor with ball bearings will only have to be looked at once a month. This change is more noticeable when the motor is installed in a very dusty place as it may then be necessary to clean the oil wells and renew the oil every week. The 162 DIRECT-CURRENT MOTORS AND GENERATORS *7 method of mounting the ball bearings in the housing of the bearing brackets is shown in Fig. 3. It will be seen that the housing caps on the right hand or pulley end bracket must be removed before the bearing bracket can be removed from the frame. This type of con- struction is used by the majority of manufacturers, although there are some that do not use the inner housing cap, but machine the housing in the bearing bracket as is the case in the left-hand bearing of this figure. It is more difficult to dismantle and assemble a machine where this type of construction is used, because both ball bearings must be removed before the brackets can be removed. The method of assembling the bearings on the shaft is shown in Fig. 4. It will be seen that a smaller ball bearing is used on the Ω Fig. 4. Assembling Ball Bearings on Shaft Courtesy of the SKF Industries commutator end of this motor than on tne pulley end. The shaft in this particular case is ground a few thousands smaller than the inside diameter of the ball bearing so that it can be pushed into place and then locked by the clamping ring that the assembler has 163 8 DIRECT-CURRENT MOTORS AND GENERATORS in his left hand. The shaft is usually made so that the bearing is a light press or drive fit on it, while the inside of the housing is made so that there is a light sucking fit between it and the outer race of 100001 10 10 30 A B с Fig. 5. Method of Locking Ball Bearings on the Shaft the bearing. The inner race is locked on the shaft and revolves with it by means of a narrow nut which is locked on the shaft by means of a wire spring, or two nuts as shown in Fig. 3. In Fig. 5 some of the other methods used in locking the inner race on the shaft are shown. In handling ball bearings care must be taken to see that no grit or dirt is allowed to get in the raceways. After being removed from SHAFT BURA Vaat B BABBIT OR LEAD A Fig. 6. Wrong and Right Methods of Installing Bearing on Shaft Courtesy of New Departure Manufacturing Company ur the shaft they should be cleaned in gasoline or kerosene and then given a spin to see if they work freely and if they can be used again in this motor. When they are to be used again, they should be 164 DIRECT-CURRENT MOTORS AND GENERATORS 9 lubricated with vaseline or ball-bearing grease and revolved several times to work the lubricant into all parts of the bearing and then wrapped in clean brown or white paper until ready to be replaced on the shaft. The best method of placing bearings on a shaft is to use a small arbor or hand press and push them into position. When this method cannot be used, secure a copper or brass tube that will slip over the shaft, as shown at C, Fig. 6, and the bearing can be forced into place by hammering the tube. Do not under any cir- cumstances strike the outer race with a hammer or rawhide mallet or any piece of metal as this will only cause the inner race to dig in the shaft, as shown at A and B, Fig. 6. The bearing may also be forced into position by holding a piece of hardwood against the inner race and striking the wood with a hammer, as shown in Fig. 7. INNER RACE OUTER RACE SHAFT HARD WOOD BLOCK Fig. 7. Assembling Bearings with Aid of Wood Block Courtesy of New Departure Manufacturing Company Lubrication of Ball Bearings. The ball bearings used on electric motors may be lubricated either with oil or a good grade of ball bearing grease or petroleum lubricant. When the manufacturer has provided an oil cup, a good grade of mineral oil should be added when necessary. It is advisable to use oil instead of grease when possible to do so, especially on high speed motors. When the manufacturer has not made any provision for supplying oil or grease, the outer housing caps should be removed from both bearings about every six months and the old grease washed out with clean gasoline or kerosene and the bearing inspected to see that it is operating properly. The bearings should then be packed with a grease, made 165 10 DIRECT-CURRENT MOTORS AND GENERATORS especially for ball bearing work, using care to see that the bearing space is filled completely. When filling the bearing box, the motor should be revolved slowly in order to force the grease into the other side of the bearing. The ordinary vaseline or petroleum jelly can be used when the ideal grease for ball bearings cannot be obtained. When the caps of the bearing housing of the motor are fitted with pipe plugs, a grease gun, such as is used for lubricating automobiles, can be used to force new grease into the bearing housing. The old grease will be forced out around the shaft, where it can be wiped off with rags. The armature of the motor should be revolved while the grease is being forced into place in order that all parts of the bearing will be filled. The motor should then be run for several minutes in order to force the old surplus grease out around the shaft, where it can be wiped off. REPAIRING FIELD COILS Grounded Field Coils. The field coils should be tested for "grounds" by applying twice normal voltage between the windings of the fields and the frame of the machine. This can be done with a testing transformer or by securing the higher voltage from some other circuit. When there is no high voltage available, the insula- tion can be tested by connecting a voltmeter in series with the field winding connected to one side of the line while the other side of the line is attached to the frame of the machine. If the voltmeter should indicate nearly the same voltage as when attached to the line, it indicates that the field coils are making contact with the frame. Another method is to take a pair of test leads which have a small lamp in series with each side of the line and attach one lead to the field windings and the other lead to the frame. Then if there is very much current flowing through the circuit the lamps will burn dimly or brightly. While the test leads are attached to the field and frame, each coil should be tried to see if it can be moved on the pole piece and thus discover where the defect exists. It may be necessary to remove the coils from the pole pieces or open the con- nections in the leads between the coils in order to locate the defective When the defective field coil is wound on a metal spool or bobbin, it is necessary to rewind the coil. Where the "ground" is due to defective insulation between the field windings, it can often one. 166 DIRECT-CURRENT MOTORS AND GENERATORS 11 be repaired by inserting a piece of horn fiber between the coil and the frame, or by retaping the coil. Short or Open Circuited Field. The shunt and series fields should be connected to a circuit that will pass the normal current through their windings. The voltage drop between the two terminals of each coil should be obtained with a voltmeter. The readings for all coils of the shunt or the series winding should be the same. The coil with a low reading would indicate either that it did not contain as many turns of wire as the others, a larger size of wire was used, or some of its turns were "shorted." The defective coil should be removed and tested for short circuited turns on the E-shape coil tester shown in Fig. 8. The top yoke of the tester is easily removed Ħ HANDLE *2** ס נכot O (COIL B 6"-2" - ·18". 1014 COIL A 6" 2" YOKE FIBER COIL C 3/8 BRASS DOWEL PIN COIL B COIL C FOO FUSES COIL A Fig. 8. Device for Testing Field Coils TELEPHONE RECEIVER 110-VOLTS A.G by means of the handles so that the coil to be tested can be slipped over one of the outer legs, and the yoke is replaced. The two brass dowell pins make it possible to place the yoke in the proper position. The coil A on the center leg is composed of 250 turns of No. 12 B & S gage double cotton covered wire and the coils B and C each have 100 turns of No. 30 enamel single cotton covered wire. The coils B and C are connected so that the voltage induced in them will buck each other and normally there will be a very small current if any flowing through the telephone receiver, which will only pro- duce a slight hum. When a coil that has a short-circuited turn in it is placed over the outer core or leg and the yoke is replaced, a magnetic unbalance will occur and the telephone receiver will give off a louder sound or noise than otherwise. A push button switch should be located in the wooden base so that the current can be turned on only for a few moments at a time. The A coil should be 167 12 DIRECT-CURRENT MOTORS AND GENERATORS connected to a 110-volt alternating-current circuit, although where direct current is the only kind available, a large door bell can be connected in series with one of the line leads and produce an inter- rupted current. The door bell should be located far enough away from the testing outfit that it will not interfere with the sound given off by the telephone receiver. An open circuit in the field coil will not allow any current to pass through that circuit. It can be located by momentarily touch- ing a copper wire jumper to the two terminals of each of the coils until the defective one is located. When the shunt field is wound with small wire, the defect may be where the terminal is attached to the coil, and the connection can be resoldered. When the open circuit is inside the winding of the coil, it is necessary to rewind the coils with new insulated wire. Rewinding Field Coil. When it is necessary to wind a field coil to replace a defective one, the insulation should be cut so that F A M - B - -B My A --THIS SIDE NEXT TO ARMATURE D O Field Coil Data Dimensions with Insulation Removed:- Inches B Inches D Inches F Series Field Winding Turns, No.. A C E Location Remarks Shunt Field Winding Turns. No.. (Place circle around kind of wire) Location Remarks Insulation Used. Inches Inches Inches SCC DCC ESC |--E →→ Fig. 9. Recording Field Coil Data the dimensions shown in Fig. 9 can be obtained. These dimensions are taken so the person winding the coil will have a guide and they must not be exceeded, or the completed coil will not fit in the machine. SCC - SSC DCC - DSC ECC-Enamel 168 DIRECT-CURRENT MOTORS AND GENERATORS 13 3 A block of wood having the thickness of the A dimension and a length and width of the B and C dimensions is obtained. When a machine for winding field coils is available, a hole is drilled in the center of the B and C dimensions and the block is clamped between the two face plates of the machine. If such a machine is not avail- able, the sides for the former can be made from 2 inch or 1 inch boards. The dimensions of one board will be twice the D dimensions added to both B and C, while the other one will be twice the E dimension added to B and C dimensions. One board is nailed or fastened on one side of the block and the other one on the other side. The center of the coil former is located, and it is clamped between the center pins on a lathe; one side is fastened to the face plate so it will revolve when driven by the lathe. The lathe is placed in back gear or slow speed in order that the winder can con- trol the wire while it is being wound on the former. A strip of heavy paper the width of the former is cut and wound around it, and six or eight strips of cotton tape about a foot long are inserted under this band and their ends are fastened on the outside of the sides of the coil former. These strips of tape are tied around the coil when the winding is completed in order to hold it in place when the former is removed. It is best to use rubber covered wire of a size smaller than that used in winding the coil, for the external leads from the coil. When the wire used on the fields coils is smaller than No. 17 B & S Gage, number 18 rubber covered lamp cord should be used. The length of the leads should be such that they can make one turn around the coil or former and should be carefully soldered to the wire used in winding the coil, care being taken to obtain a good connection. When the wire for winding the fields is larger than number 20, it should be wound in layers, otherwise there will be difficulty in wind- ing the correct number of turns in the space allowed. When the coil has been wound so that the last layer is level with the top of the former, that side of the coil should be tapered by placing one less turn on that side in each layer; then when the top of the other side of the former is reached, it should be tapered in like manner. As soon as the correct number of turns have been wound on the coil and the external leads connected to it, the ends of the cotton tape should be drawn over the coil and tied tightly. The series 169 14 DIRECT-CURRENT MOTORS AND GENERATORS field winding is sometimes wound next the pole piece and under the shunt winding, on the top or along side of the shunt winding and near the armature side of the coil, as shown in Fig. 9. When the series winding is on the inside or along side of the shunt, its winding should be wound in place before starting the shunt winding. With this winding on top of the shunt, it should be wound in posi- 'tion before the coil is removed from the former. The completed field coil is dipped in insulating compound and baked and then the required layers of insulating tape wrapped in place. Assembling Field Coils. When the new field coils are being baked, the old coils should be dipped in the insulating varnish or else painted with a coat of paint that will match the new coil. All dirt and oil should be removed from the old coils before painting, and where this cannot be done the outer layer of old tape should be removed and new tape applied. This extra work, while it may not be necessary, is well worth the cost, because it will give the motor the appearance of a new machine, and the customer will be well satisfied with the work. When all the field coils have been removed from the machine, and no record has been made so as to aid in identifying their location, it is best to lay them out on a table with the side that goes toward the armature upward and make temporary connections between coils in the same manner as when they are connected in the machine. The coils will appear similar to A, Fig. 10. The coil marked S1 is the one on the lower left-hand pole piece when looking from the commutator end toward the driven or pulley end. This is the same as cutting the machine through the vertical center line and laying the right-hand half on the right side and the left-hand half on the left side. Thus poles numbered 1 and 4 have the same position as when they are in the machines. The inter- poles or commutating poles are numbered in similar manner, and number 1 is between No. 1 and No. 2 main pole as will be seen at D, Fig. 10. The letters I and 0 indicate which is the outer and which is the inner turns of the coil. In connecting the coils together it will be seen that the O end of one coil is connected to the 0 of the next coil, and the I ends in like manner. At B, Fig. 10, the leads from two of the coils have been crossed inside the taping of the coil so that the crossing of the leads as shown at A, Fig. 10, will be eliminated. In all these sketches the I 170 DIRECT-CURRENT MOTORS AND GENERATORS 15 lead of the left-hand and the right-hand coils while connected in the machine are not shown connected here in order to convey the manner of making the connection. In these figures the left-hand arrow con- N 4 QOPQ 100 S N 4 N 2 N 2 N 2 S F- N 4 0 D ww. A ப Fig. 10. Method of Connecting Field Coils in a Machine S S 3 A F+ B F+ C nects with the V-shaped end of the lead on the right. In some machines the space for the end connections is very small, and then part of the coils are connected together on the front or commutator 171 16 DIRECT-CURRENT MOTORS AND GENERATORS end and part are connected on the rear end of the pole pieces, as shown at C, Fig. 10. The interpole, or commutating pole, winding is usually wound out of strap copper in the larger sizes and the con- nection between coils is usually made with this material, which is then insulated with cotton tape and insulating varnish. The strap copper connections occupy less space than cables and can be bent to any desired shape. The usual method of connecting the inter- poles is shown at D, Fig. 10. The interpole of a motor is connected so that it has the same magnetic polarity as the pole tip nearest it in a direction back against the direction of rotation. On a generator the commutating pole has the same magnetic polarity as a pole tip nearest it in a direction forward with the rotation. Thus the polarity of the main and commutating poles shown at C and D, Fig. 10, is for a motor running in a clockwise direction or a generator running in a counter- clockwise direction. A motor may run in the opposite direction from that for which the polarity of the poles were figured. In this case its direction should be reversed by reversing the leads connected to the brush holders, which will make the direction of rotation and polarity cor- rect. If a generator should give the opposite polarity from that originally calculated and thus reverse the magnetic polarity of the interpoles, it can be corrected by interchanging or reversing the leads at the brush holders. When it is desired to reverse the direc- tion of rotation of a machine, the leads from the armature and inter- pole should be interchanged where they are connected to the line. REPAIRING ARMATURE Determining Extent of Repairs. The first thing to do with an armature as soon as it has been removed from the machine is to locate the defects. When the machine appears to be ten to fifteen years old and there are several defects-such as open circuits in the coils, coils grounded, and commutator has deep grooves or ridges- it is best to rewind the armature and not spend any time in attempt- ing to repair the defects. The portion of the shaft that fits in the bearings will undoubtedly be worn and grooved due to the wear from the oil ring and will have to be repaired. It will be well to consider whether the machine is worth the cost of repairs, which is 172 DIRECT-CURRENT MOTORS AND GENERATORS 17 always higher on the older types of machines, or would it be cheaper to scrap the old machine and apply its value towards the purchase of a modern machine. The life of an electric motor or generator is from ten to twenty years and the depreciation is figured at 8 to 12 per cent of its original cost each year. Thus if the cost of repairs plus its value as scrap is more than one-third of the cost of a new machine of the same capacity, it would be cheaper to purchase the new machine. The new machine will undoubtedly have a higher efficiency, which will reduce the operating cost several per cent. When the windings appear to be in good condition and the defects appear to be confined to one or two coils, the armature can then be repaired without rewinding. Should the defects be such that it is necessary to replace several coils, it is best to rewind the armature, because the insulation on the coils is very brittle and due to handling they will have to be reinsulated. One or two coils in an armature that may have a short or open circuit in them can be easily cut out, and the machine will operate without them. The methods used in locating defects are the same as those described in the section on "Winding Armatures." Locating Defective Coils. An open circuit in an armature of a machine is usually first indicated by sparking at the commutator. A vicious greenish-purple spark will usually appear at each brush as the open-circuited coil passes from one pole to the next one. The commutator bars that are connected to this coil will be rough and burned and the mica between them will be burned out to a consid- erable depth. With a wave instead of a lap winding it is more difficult to locate the defect because in a four-pole machine there may be two bars that are blackened or the mica may be burned out between commutator bars diametrically opposite each other. The method for cutting out an open coil is shown in Fig. 11. In this illustration coil 3 is the defective one. When the defect is due to an open circuit, the commutator bars 3 and 4 can be connected together by soldering across the riser or tang of these bars. It is better however to remove the leads A and B from bars 3 and 4 and connect a wire jumper across the two bars. When there is a short circuit in the coil and there is more than one turn in each coil, the wires should be cut as shown at C. The ends of the leads at A, B, and C should be insulated with tape and bound to the other coils so 173 18 DIRECT-CURRENT MOTORS AND GENERATORS that they will not be thrown outward when the armature is revolving and strike other coils and wear the insulation off them. This dead ď e I coil will have voltage generated in it the same as the others, but no current can flow because the circuit is open. MAUS DATAKS | || / // // / // | |/ ///// T⠀⠀⠀⠀⠀ [1]|||||||||||||||||||||||||//| EL mnuu ENEMEDADE 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 [I]//[!!!]]]] Summm!!!}/}} ………………………… FIED 1 !………………↓↓↓↓↓ÿÿÿ↓↓…2……üüs Fig. 11. Method of Cutting Out Coils in a Lap Winding |||||||| ELE C 1 2 3 4 5 Quman|X|||$||¶//}[S] INDERSIA \…↓↓↓↓ÿÿÿÿÿÿÿÿ↓↓…#↓/UMMAS LEL 2 3 4 5 |||||||| Samm D= -C*0=U= משש WITŸŸk↓↓↓↓↓↓↓↓THAULING GAMINIMIIIFIRDIRI Qum/770/ EMES mit 4-mind • SILT!!14-20-.-⠀⠀0}}} |||||| BUZI: munit Sim 10: Communa |||||||| #ITI Summa ununi SEIBIFONI #///////////// | || ww E mus STUULLITTUALI SA mumm mu !!!!!!!!! Mun NUI/EB……||||||||||||||||||OUN> TEDEDEIVIAINA S|||||||||||||||||||||||||⠀⠀⠀⠀⠀⠀ FEISEKSISI (HOTEL||||||||||BERAS FIE FIN MILITIAN MIK H #L IN --e 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 C Fig. 12. Method of Cutting Out Coils in a Wave Winding It is not an easy job to repair or cut out an open or short-circuited coil in a wave or series winding. There are several ways of cutting 174 DIRECT-CURRENT MOTORS AND GENERATORS 19 out the defective coil, but the simplest and easiest way is to discon- nect the leads from the defective coil and the commutator bars to which it is connected. The leads from coil 14, which are con- nected to bars 8 and 20, are removed and a jumper connected to these commutator bars. When there is a short-circuit in the coil, the rear part of the coil can be cut open like the coil in Fig. 11. Recording Winding Data. There are certain data that should be taken from the winding and recorded before attempting to tear the winding from the armature. If the necessary data are not recorded at this time, there will be great difficulty in making the proper connections when the new coils are placed on the armature. It may also happen that the one who removed the old winding is engaged on some other work and some one else must connect the winding. It is also desirable that there be a record of the winding data kept in the repair shop, because frequently a duplicate armature may come in for repairs which has been rewound, after leaving the manufacturer's works with the incorrect size of wire or number of turns, and this error can be discovered and the correct winding applied. This will enable the motor to give more satisfactory service than before, thus pleasing the customer, who will favor that particular repair shop with more business. It is of great help to the winder if some form is provided where he can fill in the required data taken from the old winding. A form 5.0. M. P__________ Poles Generator Motor Serial No.. No Slots Wires per Slot Wires in Parallel. Size of Wire Lbs. Scrap. Bands on Core_ Bands on Coils Customer Manufacturer. Volts Interpoles. Speed Amperes. No. Coils. Turns per Coll Formed. Length 1 Turn Shaft Marked No. of Wires. No. of Wires Type. Shunt. Series, Comp. 40° or 50°C "Hr.} Rating. Cont. Na Comm, Bars. Wires per Bar. Wide x Length of Leads Core Marked Size of Wires. Size of Wires. Cost $ Deep INCHES → H ] SLOT- ✯ OF COIL SPAN> SLOT A 。° Fig. 13. Method for Recording Armature Data similar to that used by one of the largest motor manufacturers who operate a series of service or repair stations in a number of the large cities is shown in Fig. 13. This blank form could be printed on 175 20 DIRECT-CURRENT MOTORS AND GENERATORS letter size paper, 8 x 11 inches, and then filed away with the corre spondence or other papers. However, this size is not very convenient to the winder, a card about 4 inches by 6 inches or 5 inches by 7 inches being much easier to handle. When the 4 x 6 card is used, the data can be recorded on the face of the card and the diagram of connections of the coil placed on the reverse side. With the 5 x 7 card, the data and diagram can be recorded on the face side of the card. The cards can be filed away under the name of the different manufacturers, and in a short time a complete record of the windings of the different standard makes of the machines can be obtained. When the same armature comes into the shop for rewinding the second time, it is not necessary to spend the time in recording the data and a helper can be put to work removing the winding. Another very important thing is the fact that the winder may make a mistake and not wind the armature properly, and if no record was kept, this mistake would be repeated every time it was rewound. There will occasionally be armatures that come in for repair where some inexperienced winder has attempted to modify the windings for some other speed or voltage from that on the nameplate and the marking has not been changed on the nameplate. When the customer desires that the motor operate at the speed or voltage shown on the nameplate, the correct winding data should be obtained from the manufacturer. When writing the manufacturer, all the data on the nameplate should be given and in addition all the data shown in Fig. 13, which was taken from the armature. This will enable them to identify the machine in case the serial number had been changed, which is sometimes done by unreliable second-hand dealers. While some manufacturers do not care to give out the data of their machines, they are nearly always willing to check the data that you obtain from the machine with their specifications and give you the correct data. They realize that, unless the correct winding is used, the machine will not perform satisfactorily, and this will reflect on their good name. When the repairing of motors is done by the company owning and operating them, the correct winding data should be secured for each and every motor in the plant and kept on file where it can be easily consulted when necessary to repair the motor. When the maintenance and inspection of the electrical equipment in a small factory is done by a motor repair or service ! 176 DIRECT-CURRENT MOTORS AND GENERATORS 21 company, they should have the data in regard to the windings of all the motors in their customers' plant, so that they can render prompt and reliable service. In the skeleton outline of the core and commutator bars shown in Fig. 13, it will be seen that there are two groups of commutator bars, marked A' and B'. In group A' the commutator bars are lined up so that the center line of the slot is on the center line of the bar, while in group B the center line of the slot is in line with the mica between the bars. In Fig. 13 the data on the first four lines of the card can be obtained from the nameplate on the motor or generator as the case may be. It is also desirable to know whether the motor is designed for 40 or 50 degree Centigrade temperature rise above that of the room and also if the machine is intended for continuous service at the rating marked on nameplate or whether for a shorter length of time. This last item will be of service in case the motor burns out again and there is a dispute with the customer, because that par- ticular motor may have been designed for a 15-minute rating and naturally would soon burn out if operated at its full load continu- ously. The number of wires in one slot will be of service in checking to see that the other data is correct. This is equal to two times the number of coils per slot, times the number of turns per coil, times the number of wires in parallel. The number of wires per bar is the number of conductors connected to the commutator bars, and is twice the number of wires in parallel. The length of one turn and the length of the leads is of service to the winding department, in that it would be possible to start at once to wind the loops should the machine come into the shop for rewinding a second time. The method of filling in the diagram on the reverse side of the card is shown in Figs. 14 and 15. In filling out this diagram the following should be kept in mind, and the armature and diagram should be marked accordingly. Mark the tooth on each side of the slot that contains the bottom side of the coil with X. Mark the tooth on each side of the slot that contains the top side of the coil with XX. Mark the end of each commutator bar with one dent from a center punch that has a lead from the top or bottom side of the coil under consideration con- nected to it. 177 22 DIRECT-CURRENT MOTORS AND GENERATORS 麻 ​ DI 日 ​SOLDER HERE -A- 無 ​D. 5049 -C- C ↓ A 띵 ​B' | A DB 遅 ​B END OF COIL TAPED UP A' B' D 448円 ​5655 18 T T B W |20|19|18|17| g · B · -D- JOE -F- XIX LE 5 JIF ·E. Fig. 14. Method of Connecting Coils When Brushes Are Under the Poles λ [A B' ▸ A B SOLDER HERE A' B 178 DIRECT-CURRENT MOTORS AND GENERATORS 23 Mark with two punch marks the bar that is on a center line with the side of the coil marked with one X. When the center line is on the mica between bars, mark each bar on both sides of the mica with two punch marks. Mark with three punch marks the bar that is on the center line of the slot containing the top side of the coil and marked XX. When the center line of the slot falls on the mica between bars, mark the bar on both sides of the mica with three punch marks. When the armature has a dead coil, always use this slot for taking data and recording the information on the diagram. When the commutator is to be removed for repairs do not punch mark the bars. The diagram on the card, in addition to showing the same mark- ing as the armature, should have recorded the slot numbers for the B AD 56 A 47 B A X SLOT / 0 AA A [xx SLOT 17 XX TOP A 234 B OF SLOT -* Co -B- COMMUTATOR BARS SHOWING HOW TO LOCATE COM- MUTATOR BARS FROM CENTER LINE OF A SLOT ON A SPIRAL OR SKEWED CORE -D- A & OF CORE -C- Fig. 15. Method of Connecting Coils When Brushes Are Not Under the Poles bottom and top sides of the coil, the number of the commutator bar to which the leads are connected, and the number of the commutator bar opposite the center line of the slot in which the bottom coil is located. The slot containing the bottom side of the coil is usually 179 24 DIRECT-CURRENT MOTORS AND GENERATORS marked number 1, and the commutator bar connected to this coil should also be marked 1. The distance that the winding extends on the back side away from the core should be recorded so that when rewinding the back side of the coils will not be allowed to exceed this limit. If this is not watched, the back side or end of the coils may strike on the frame of the machine when it is running and wreck the armature windings. In Fig. 14 the method of marking the diagram for a Westing- house Type SA armature having 31 slots and 31 commutator bars is shown at A. It will be noted that the top side of the coil is in slot 8, which is marked XX, and the top lead of the coil is connected to commutator bar 17. It will be seen that the center line of the bottom slot is on the center line of the commutator bar number 6, which is marked with two punch marks. The letters A, B, C, D, and E are used when it is desired to tabulate the data from a number of windings into tables where it can be easily consulted. The letters A and C always represent slot and commutator bar 1, which is always the slot containing the bottom side of the coil and the bottom lead. In this winding the commutator pitch is what is known as a long pitch, that is, the pitch is 16 bars. If the pitch had been 15 bars, or 1-16, it would have been known as a short pitch. Here is a case where if the winder had only marked the commutator bars and had not marked the slots in which the coil was located or the com- mutator bar opposite the bottom slot, it would have been very easy to insert the coils in the slots diametrically opposite and then connect the leads to the marked bars. The coil pitch would then be 1-16, and the motor would run in the reverse direction; or in case of a generator, its polarity would be reversed. If the machine had inter- poles or commutating poles, it would be necessary to reverse them and connect them to the brush holder that is of opposite polarity. This condition can only happen on a four-pole machine, but this condition should be watched because the majority of motors are four-pole machines. In Fig. 14 the connections B are given for a Westinghouse 50E frame, 220-volt crane or railway motor, which was used quite ex- tensively in mine work. This is a lap winding with 52 slots and 156 coils and commutator bars. The commutator is located on the 180 DIRECT-CURRENT MOTORS AND GENERATORS 25 shaft so that the center of the mica is on the center line of the slots. The commutator pitch is 18-19, or what is more often called or known as a 1-2 connection. In this winding the leads are connected to bars opposite the center line of the two sides of the coil, although they may be shifted either to the right or left, and it will be necessary to locate them with reference to bar E. In Fig. 14 C is similar to A except there are three coils per slot instead of one coil per slot. This data is taken from a Westinghouse type R-7 motor which has 37 slots and 111 commutator bars. It will be seen that the center line of the slots falls on the center of the bar as in A, Fig. 14, which has one coil per slot and would be the same when there are five or seven coils per slot. When there are two, four, or six coils per slot, the center line of the slot would be in line with the mica between bars as in D, Fig. 14. There are 47 slots and 93 bars on this armature and one of the coils has the ends of the leads cut off and taped up and is referred to as the dead coil. When an armature contains a dead coil or special connections, that coil should be chosen for the diagram. It may happen that the commutator contains an even number of bars and it is desired to use a wave winding, especially if the winding is being changed from a lap winding. The method of making the connections is shown in E and F, Fig. 14. In E one end of the coil is dead ended and the other side is connected to the commutator bar. A jumper is connected from this lead to the adjacent top lead and the connection is soldered. In F the top part of the idle coil is connected to the commutator bar while the bottom lead is connected to the same commutator bar as the other coil. In this case bar 55 has only one lead attached to it, which is a top lead. In A, B, C, D, E, F, Fig. 14, the commutator throw is equal on each side of the center line of the coil in the slots and the brushes that bear on the commutator bars will be opposite the center line of the pole pieces. It is sometimes desirable for mechanical reasons to locate the brushes at some other location than opposite the center line of the pole pieces. Such is the case in the General Electric 51A motor, which has the coils connected as shown in A, Fig. 15. This armature has 37 slots and 111 commutator bars. The bottom lead is connected out straight from the slot to the commutator bar, while the top lead has all the throw. Right-hand coils are used on 181 26 DIRECT-CURRENT MOTORS AND GENERATORS this armature instead of left-hand coils as in the preceding diagrams. An armature coil is called a right-hand coil when the side of the coi! that is placed in the top half of a slot is to the right of the side that goes in the bottom half of the slot. A left-hand coil would be the reverse and the top side would be to the left of the bot- tom side. The bottom lead of the winding may be brought out near the center of the coil as in B, Fig. 15, which is the winding of a General Electric type 1000 armature which has 93 slots and the same number of commutator bars. When the length of the leads to the commu- tator bars from the top and bottom sides of the coils are not the same, care should be taken to give on the data sheet the correct length for the top leads and for the bottom leads. This information will enable those making the coils to provide leads of the correct length, which are usually about two inches longer than the exact length which is recorded on the card. This extra length will allow the winder to grip the wires with a pair of pliers and insert them in the slot in the riser, while if a longer length was used, more time would be required to remove the insulation and the wasted copper wire would be greater. Reducing the extra length of the leads below two inches will make it harder for the winder to insert the leads in the slot, and this extra cost will be several times the saving in copper wire. The method of filling in the diagram for a lap-wound armature, having 32 slots and 64 segments with the connections shifted so that the brushes are located midway between the pole pieces, is shown in C, Fig. 15. The coil is right handed with a span of slots 1 to 17. When the slots of the core are spiraled or skewed, as shown in D, Fig. 15, it is more difficult to determine which bar is opposite the slot in the core. In this illustration it will be seen that the center line from the slot is extended from the middle point of the core and not from the commutator end of the slot, as is sometimes done and which will cause trouble. A combination steel square, steel scale, or a piece of straight key stock will be of assistance in locating the commutator bar opposite the center of the slot. The scale or straight edge should be held or clamped to the core so that the amount of the tooth visible at one end of the core is equal to that under the scale 182 DIRECT-CURRENT MOTORS AND GENERATORS 27 or straight edge at the other end of the core. In D, Fig. 15, the edge of the scale would be in line with the edge of one tooth on the back side of the core and the front edge of the tooth on the other side of the slot. Removing Old Coils. When removing the old coils from an armature that is to be rewound, one of the coils should be removed very carefully so that it can be used as a sample by those that are winding and forming the new coils for that armature. In securing this coil the wedges should be driven out of the slots and the top half of the coil cut at both ends and that portion in the slots pried or pulled out of the slot. This process should be repeated for one or two more slots than the coil span, so that the special coil can be removed for measurements. The leads should be unsoldered from the commutator bar on this particular coil before it is removed from the slots. After removing the desired coil for measurement, the remaining coils are cut flush with the commutator side of the core and then pried or pulled out of the slot. The leads to the commutator are cut off at the edge of the coil and unsoldered from the commu- tator by heating the riser with a blow torch or better still with a heavy soldering iron. Care should be taken to remove all the solder when the leads are removed so that there will be room to insert the wires of the new winding. A broken hack saw blade that has its edges ground square and sharp is useful in scraping the soft molten solder from the slot in the riser. When using a blow torch to heat the commutator risers, do not allow the inner blue cone part of the flame to come in contact with the copper, or the copper will be oxidized and become very brittle, which will give trouble when the new winding is connected. Before removing the wedges from the slots they should first be loosened by hammering down on a narrow steel bar that is held on them near the teeth. They are then driven out by holding a hack saw blade on the wedge and hammering the end of the saw blade so that the teeth will be driven into and grip the wedge as it is driven out. When the armature windings are made of copper bars or ribbon. it is sometimes desirable to use the same copper in the new winding. In removing such windings the leads to the commutator should first be unsoldered, all the slot wedges removed and then each coil should be pried out of the slot, using care not to bend the coil any more than 183 28 DIRECT-CURRENT MOTORS AND GENERATORS is necessary. The old insulation must be removed from the coils completely before they can be insulated. If high pressure steam is available, the coils can be placed in a sheet metal oven or container and live steam turned on from twelve to twenty-four hours, which will cook the insulation and then it can be peeled off very easily. The insulation is sometimes burned off the wire or copper, but this is not good practice because there is a tendency to overheat the copper and thus destroy its usefulness. On railway and mine haulage motors a number of the large manufacturers can furnish a complete set of armature coils and all the insulation required to rewind the motor is cut exact size. These materials are of the same quality as those used in the original winding. When it is possible to secure the coils and insulations in this manner it should be done, as it is more economical and they will give better service than those not adapted for this special work. Where there are a number of these motors of the same make and size in service, a spare set of the coils and insulations should be carried in stock. Winding and Forming New Coils. The majority of motors and generators of medium size are wound with a formed coil, and it is desirable to rewind the armature with the same kind of a coil. When the shop is equipped with a loop winder and coil spreading machine, such as shown in the section on "Winding Armatures," the new coils can be easily constructed. Without this equipment it is necessary to wind the loop and spread it to the desired shape by hand. A simple device that can be easily constructed by any repair shop is shown in Fig. 16. This frame is constructed of one inch by three-eighths inch steel or iron bars and can be attached to the slow speed shaft of a small back gear motor that has a large speed re- duction. 3 8 The material required for this frame consists of 9 feet of 3 inch strap steel or iron, four inch carriage bolts 14 inches long, nine 3 inch bolts or cap screws that have at least 2 inches without threads, one foot of round steel 2 inches in diameter which can be cut into disks half an inch in thickness, eighteen set screws inch in diameter and inch long, twenty-two inch hexagon nuts, and fifteen inch iron washers. The 2 inch disks are drilled off center with a ginch drill, and a hole is drilled and tapped at right angles for a inch set screw. In the small detail sketch the assembly of the 3 8 3 8 184 DIRECT-CURRENT MOTORS AND GENERATORS 29 disks and nuts on the bolt which fits in the slots is shown. The right-hand hexagon nut is turned on the bolt as far as possible and the threads at the back side of this nut should be flattened slightly with a blunt chisel in order to prevent them loosening up. The face of the bolts that bears on the sides of the slot should be nicked with a sharp cold chisel the same as the side of the slot, in order to prevent them from sliding out of position. The head of the bolt is cut off so that the outer disk can be slipped off easily when removing the coil that has been wound in the slot between the disks. These bolts make good guide pins that can be easily adjusted in the slots for any length of coil desired, while the adjustment for the desired coil span or pitch is obtained by adjusting the upper and lower bars **THICK 10" ……………………………………FITTI › Glen K………………………………………………………………………… 7" dej Ma HIMAT": ||18125624235JUTERII ……………18………………18(1) A……|||S|TER……13020711---2012…………………………………………28464|||||| BAR " THICK ABILITIE Zenum ANG KUITE yi DISK mic 24"- - 32' SR SEMILIE TUHIA. 182494- 341410 14……21a1a6236 SERIO2042 RIVETS סאותי SLETTERSKOLA AUTAN [ITEƒ41484) '2016||||||||||| 23 Fig. 16. Coil Former or Winder {···Ð·Ð·Ð´·{ }·ØDGØT·TT·ÐIH 7 9 10 7 8 9 12 F LL. TURN SKEIN LEFT TO RIGHT 10EE 12 1·1·1®£•]}]·7·7·1·1°Ð·¶774««I 8 9 10 15 10 16 13 E Fig. 17. Method of inserting skein-type coils in stator slots. 12 13 14 much as when the same turn is made on both the front and back ends of the core. With some windings it is immaterial whether the half turn is made the same on both ends or not, because there 206 WINDING ALTERNATING-CURRENT MOTORS 17 is sufficient space for the winding on the core. The skein is then inserted back through slots 5 and 12 as shown in E, Fig. 17, and again twisted and passed through the next slot-an operation which is repeated until the slots are filled as shown in F, Fig. 17. This completes the winding of the first skein in the slots. The second skein, which in this particular motor is 88 inches in length, is then passed through slots 3 and 14 as in G, Fig. 17. Its end is then given a half turn and passed back through the same slots and the operation repeated until the slots are filled according to the winding data given in Fig. 16. It will be noted from the data that there are two coils of fifteen turns each in slots 1 and 16. TO AUTOMATIC STARTING SWITCH BOLT HOLE- - ·ROTATION- 910 18 -MAIN WINDING TWO POLE SERIES CONNECTION CLOCKWISE ROTATION WHEN FACING SWITCH END STARTING WINDING TO AUTOMATIC STARTING SWITCH EXTERNAL LEADS MAIN WINDING 놀 ​4 休 ​MAIN WINDING Fig. 18. Wiring diagram for the stator of a single-phase motor. STARTING WINDG When completing the main winding of the first pole, the skein is placed in slots 1 and 16 only once, the same as shown in A, Fig. 17, for slots 6 and 11. When the main winding is placed on the other pole, which is diametrically opposite it in the stator core, the end of the second skein will lie in the top half of slots 1 and 16. The main winding for all poles is first placed in position and the starting winding is afterwards inserted in place. The starting winding is inserted in place in a manner similar to the main winding. The first side of the starting winding is passed through slots 6 and 26 and then doubled twice through slots 7 and 25 and 8 and 24. On this winding, which does not contain nearly as much wire as the main winding, it is only neces- 207 18 WINDING ALTERNATING-CURRENT MOTORS sary to use one skein; the other half of the starting winding, which is diametrically opposite, is passed through slots 11 and 21 once and then doubled back twice through slots 10 and 22 and 9 and 23. A type of winding diagram used by several manufacturers for this particular connection is shown in Fig. 18. In this diagram the winding is definitely located on the core by means of bolt holes in the stator core. One of the bolt holes is opposite the bottom of slot 5, and the other one is opposite the 5 3 30 13 15 BE 3 RUNNING WINDING 1 də đ CN CN UN ---------- TO STARTING SWITCH ·STARTING WINDING 1•1•1•1•LEZITI|||||||||||TTTHHHH 18 19 G TO STARTING SWITCH --------------------- 5 -------------------- ------------------- 3 - 1 - 1 ----P Fig. 19. Complete winding diagram showing method of connecting skein coils. " 13 15 tooth between slots 12 and 13. The bulk or mass of end connec- tions of the main winding is located midway between these two bolt holes. These holes are used in clamping the bearing brackets to the stator core and frame. A complete wiring diagram of the same motor is shown in Fig. 19. In this figure the dotted lines indicate the starting winding, and the full lines the main or running winding. The external leads marked 1 and 3 are connected to one of the line leads, and leads marked 2 and 4 to the other line lead. When the motor is standing still, the circuit through the starting winding is completed by the starting or centrifugal switch. Closing the line switch will allow current to pass through the two parallel windings and thus produce a rotating magnetic field similar to that obtained in a two-phase motor. As soon as the rotor attains about one-half to two-thirds of its normal speed, the centrifugal switch opens the circuit through the starting winding and the motor operates as a single-phase motor. 208 WINDING ALTERNATING-CURRENT MOTORS 19 Hand Winding. The insulated wire is wound directly from the spool into the slots by hand and the stator core is insulated in the same manner as when the skein winding is used. The slot insulation should extend at least 1 to 3 of an inch beyond the edge of the core. The slot numbers into which the first coil is wound are obtained from the specifications or data sheet. Assuming that the data contained in Fig. 16 is used, the first coil to be wound is the one in the center of the main winding, which is located in slots 6 and 11. The two slots M ZMY 7727 O O Fig. 20. Winding coil in slots by hand. 1 chosen on the core to represent these numbers should be located an equal distance from the two studs, or bolt holes. A piece of cotton sleeving 6 to 8 inches long is slipped over the end of the wire which forms the beginning end of the winding. The sleeving on this wire should extend at least an inch into the slot, in order to hold it in place and provide additional insulation at the edge of the core. The end of the wire with the sleeving on it is bent down over the front end of slot 6 and the wire looped at the back side of the core across to slot 11. The wire is looped as shown in Fig. 20 and another turn placed in the same slot. The loop is usually formed by holding the wire with the right hand, while the left hand is used to guide the wire into the correct position in the slot. This process is repeated until the desired number of turns are in place, which, according to data 209 20 WINDING ALTERNATING-CURRENT MOTORS 1. халта contained in Fig. 16, is fifteen turns. The wire is then looped in the same manner as before into slots 5 and 12. It is not necessary to cut the wire when looping from one slot to the next, thus eliminating splices in the coil. This process of winding the wire in the slot is continued until thirty turns have been placed in these particular slots; then the wire is looped into the next slots on each side and the process continued until the winding of that group is completed. In winding the wires in the slot, care should be taken to see that they are arranged uniformly and drawn tightly in position in the slot and across the end of the core. Otherwise the winding will be bulky and there will be trouble when assembling the stator in the frame of the machine. This is especially the case when all or part of the main or starting windings are located in the same slots. In those cases where this occurs, the main winding should be confined to the bottom half of the slot in order that proper insulation can be placed on top of this winding when placing the starting winding in position. The foregoing procedure is repeated until all the coils for a pole group-which in Fig. 16 is from slots 1 to 6 and 11 to 16-have been wound in place. The wire is then cut off from the reel or spool, being sure to allow 6 to 8 inches for connecting to the next pole group or to the external leads. Cotton sleeving is then slipped over this lead so that it will extend back into the slot an inch or two. After the winder has had considerable experience in winding single- phase machines, the skein type of coil can be wound into the slots in the core by the same method as is used for hand winding. Connecting Winding. The next operation, after all the coils of both the starting and running windings have been wound in slots of the core, is to connect the proper coils together. The beginning ends of the leads to the coils are usually brought out on the back side of the winding or on the bottom of the slot, while the ending ends of the leads are brought out on the inside of the winding. In Fig. 21 the beginning ends of the leads are marked OUT and the ending ends of the leads are marked IN. Thus the OUT ends of the leads are those pointing toward the outside of the stator core, and the IN ends of the leads are those pointing toward the center. In order that the current flowing through all the groups of coils in series will produce magnetic poles which have opposite polarity, it is necessary that the current flow in the opposite direction in half of 210 WINDING ALTERNATING-CURRENT MOTORS 21 the windings. In Fig. 7 it will be noted that in passing around the rotor core the poles are alternately north and south. In Fig. 21 assume that the current is flowing into the A lead, and that a south pole is produced by the coil in slots 1, 2, 5, and 6. In the winding which is in slots 7, 8, 11, and 12, it is desired to produce a north pole, so the current will have to flow into the ending lead which is OUTSIDE 100 DOOD'S INSIDE 1 RUNNING WINDING Do'adop 2 3 4 5 6 7 8 To'qo'n'o'o' IN OUT 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 DOGODE STARTING WINDING IN B INSIDE OUT 11 12 13 14 15 16 17 18 19 20 21 22 23 24 1 2 INSIDE IN OUT сут Fig. 21. Method of connecting coil groups of a single-phase motor. IN OUT IN marked IN. Thus the two ending ends of the adjacent pole groups of coils should be connected together. These are the two leads that are near the center or inside the rotor core. This process of connect- ing two inside and two outside leads together is repeated around the winding until all the coils are connected. In this particular motor there are 4 poles formed, which have polarity as shown in Fig. 21. It is assumed that the current is flowing into the A lead, and out of the B lead. It will be recalled that this method of connecting the leads is very similar to the method used in connecting the field coils on a direct-current machine in which the two inner leads of the coil were connected together and the two outer leads of the coil were connected together. The starting winding is connected in a manner similar to the main winding. Assuming that the current is flowing in the winding at lead C, north and south poles will be formed, which are located three slots farther to the right than the same magnetic pole formed by the running winding. After the coil groups have been connected 211 22 WINDING ALTERNATING-CURRENT MOTORS together, direct current can be passed into lead A and out of lead B, and the polarity can be checked by passing a compass around the inner bore of the stator. The compass needle should indicate north, south, north, and south. The starting winding can be tested out in like manner, and should indicate similar polarity. If one of the coil or pole groups is incorrectly connected, you would have two poles of like polarity alongside each other. The direction of rotation of a rotor can be determined by the method of connecting the windings. If the leads A and C of the run- ning and starting winding, Fig. 21, are connected to the same line leads, the rotor will turn from the running winding toward the starting winding that has the same polarity. In this particular case, the rotor will tend to revolve from slot 3 toward slot 6. The rule is that the rotor will turn from a running coil of a certain magnetic polarity toward the starting coil that has the same polarity. The direction of rotation of a single-phase motor can be reversed by inter- changing or reversing the leads of the starting winding where they are connected with the main winding to the line wires. 3 4 လိုစားစား IN OUT OUTSIDE LA RUNNING WINDING 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 || $ |||||||$||||||| $ |||| IN OUT IN OUT Fig. 22. Method of connecting winding for consequent poles. INSIDE 18 Consequent Poles. In Fig. 21 the running and starting windings are shown connected for a 4-pole motor. It is often desirable to operate a motor at half this speed, in which case there would be 8 poles. In many cases where there are a small number of slots in the stator, it is not advisable to rearrange or group the windings for this number of poles. When such a condition occurs, the winding may be reconnected to take care of this connection by the "consequent-pole” method. This method consists of connecting the coils so that the current will flow through all of them in the same direction, and thus produce poles all of the same magnetic polarity, Fig. 22. These main magnetic poles, which are represented by the letter S, produce 212 WINDING ALTERNATING-CURRENT MOTORS 23 consequent poles midway between them that are of opposite polarity. In connecting windings of this type, the lead on the inside of the core or winding is connected to the outside lead of the next coil as shown in Fig. 22. All the coil groups on the stator are connected together in this manner, which is the reverse of the standard or usual method. The starting coils are all connected to each other in the same manner as the running winding. WINDING POLYPHASE INDUCTION MOTORS Types of Windings. There are three general types or kinds of windings used on small two- or three-phase induction motors. These different windings are usually known as hand windings, basket windings, and diamond coil windings. In many of the older makes of induction motors, the insulated wire was wound directly from the spool into the slots, in a manner similar to that described in connection with single-phase motors. The use of this type of winding is being replaced rapidly by the basket and diamond coil windings. It is used, however, to a certain extent in repairing induction motors when only one or two coils are defective, and it is not necessary to rewind the stator completely. The basket winding derives its name from the fact that the dif- ferent coils overlap each other in a manner similar to the woven parts of a basket. This will be readily seen by referring to Fig. 23. These coils are formed by winding the wire on a shuttle or pins, in a manner similar to the forming of the shuttle-type coil mentioned in the section on Winding Direct-Current Armatures. Each side of the coil usually occupies a complete slot, and thus the number of coils in a winding is equal to one-half the number of slots in a stator core. This makes it necessary that the number of slots in the stator be an even number, and that the number of slots spanned by the coil (which is the pitch of the coil) must always be odd. The diamond coil winding is used more than any other type of winding, especially on motors of medium and large size. The method of forming this coil is the same as that described in the section on Winding Direct-Current Armatures, except that the leads are always brought out at the point of the diamond. This type of coil may be constructed so that each coil side will occupy a complete slot, or the top and bottom sides of two different coils may be in the 213 24 WINDING ALTERNATING-CURRENT MOTORS same slot. In the first case, the number of coils is equal to one-half the number of slots. In the second case, the number of coils is equal to the number of slots. The majority of induction motors use a partially closed slot in which the opening is about one-half the width of the tooth. This Fig. 23. Basket-type winding. makes it impossible to tape all portions of the coil as was the case with the coils used in winding direct-current armatures. For this reason, only the end portions of the coils are taped and insulated before being inserted in the slots. Insulating Core. The same precaution should be taken in removing burrs and sharp edges from the slots of induction motors before insulating the core as was taken with direct-current armatures. The slots of the stator are insulated in a manner similar to direct- current armatures. There is, however, a slight difference in detail, because on direct-current motors a fully insulated and treated coil is usually used. With partially closed slots, which are almost univer- sally used on induction motors, it is impossible to insulate that portion of the coil which is placed in the slot. These slots are lined with 0.007 to 0.010-inch horn fiber or fish paper, which is cut off flush with the edges of the sides of the teeth, as shown in A, Fig. 24. Then a layer of treated cloth, such as empire cloth or varnished cambric, is inserted inside the horn fiber insulation and extends out- side the slot approximately inch on each side in order to serve as a guide for fitting the wires of the coil into place in the slot. The thick- 214 WINDING ALTERNATING-CURRENT MOTORS 25 ness of this treated cloth, which is often referred to as a "slot slider," is usually about the same as that of horn fiber. Thus the thickness of insulation between the core and the wires is from 0.014 to 0.020 inch, which is usually sufficient for voltages up to 250. When higher voltages are used, such as 440, it is best to use two layers of the insulating cloth. HORN FIBER INSULAT- Í ION CUT OFF HERE INSULATING CLOTH రరం B C Fig. 24. Method of insulating slot and coils. TOP OF TOOTH SLOT INSULATION HORN FIBER CORE A phases 3 r.p.m. 1150 coil pitch 1-7 TOP STICK cycles 60 slots 54 Series Y connection SEPARATOR CUT HERE ALTITUDE Inserting Coils in Slots. The pitch of the coil will be obtained from the winding data or engineering specifications. Assume that the data on a particular induction motor will be as follows: D volts 220 coils 54 The number of coils and slots being the same, there will be one coil per slot or two coil sides in each slot. The number of poles formed by the winding will be 60×2×60-7200÷1150-6.25. The speed of this induction motor is rated at full-load speed, which is less than the synchronous or no-load speed. The no-load or synchronous speed would be 1200 r.p.m. and there will be 6 poles in the stator winding. The number of coils in each phase of the stator winding will be 54÷3=18. There are 6 poles formed by these 18 coils, so the number of coils in each pole-phase group will be 18÷6-3. Thus for this particular motor there will be 3 coils, which are con- nected in series with each other in a manner similar to the windings in the different slots of a single-phase motor. It is necessary to 215 26 WINDING ALTERNATING-CURRENT MOTORS know the number of coils in a pole-phase group before inserting them in the slots in order to know where to insert additional insulation between the ends of the coils where they overlap each other. Ad ka whakaut lolaple lackinkulo Imbulat Fig. 25. Inserting diamond coils in partially closed slot. When the diamond type of coil is used, the ends of the coil are taped, as shown in Fig. 25, and the leads are brought out near the point of the diamond. The leads are covered with cotton sleeving, which extends back into the coil about an inch or so, and in addition they are reenforced by two or three turns of cotton tape when the ends of the coil that are outside the core are taped. This manner of insulating the coil prevents dust and dirt from entering it and prevents electrical break-down and failure in service. The untaped portion of the bottom side of the coil is flattened out at one end near the leads with the fingers of the left hand, and this end is inserted in the corner of the slot in a manner similar to that shown in Fig. 25. This coil is then pulled into position in the slot with the left hand until the taped portion of the coil is against the core, when the lead end of the coil can be dropped into place. The coil is then pushed back into correct position in the slot so 216 WINDING ALTERNATING-CURRENT MOTORS 27 that the taped ends of the coil will be an equal distance from the core. On this particular motor the coil pitch is 1-7, so the top side of the coil will be located in slot 7. The top side of the coil is laid on top of this slot but is not inserted in the slot until the bottom coil in this slot has been put in place. 1 32 The next coils are inserted in the same manner. As soon as the bottom sides of seven coils in this particular motor have been placed in position, the top side of the seventh coil can be inserted in the slot because it is placed on top of the bottom side of the first coil. If the pitch had been 1-10 instead of 1-7, it would have been necessary to place the bottom sides of ten coils in the slots before beginning to insert the top sides of the coils. Before insert- ing the top sides of the coils in the slots, it is necessary to trim off the insulating cloth, shown in A, Fig. 24, which projects beyond the edge of the core and fold it over so that a separator, which con- sists of a piece of horn fiber approximately to of an inch in thickness, can be placed between the two sides of the coil. This insulating cloth is usually trimmed off by grasping both ends of it which project above the core and lifting the wires in the bottom of the slot up until they strike against the top of the teeth and cut- ting off the surplus insulation with a sharp knife, scissors, or a slot insulation cutter. After the insulation is cut off, the coil is forced to the bottom of the slot by gripping the two ends of the coil. The wires are arranged in order, the insulating cloth is folded over and a separator placed on top of it as shown in B, Fig. 24. The width of the separators should be such that they will make a very tight fit when hammered in place with a fiber block. After the top side of the coil has been inserted in the slot, the slot insula- tion is cut off, folded over, and forced down in the slot far enough to allow the fiber top stick or slot wedge to be inserted. It is usually necessary to hold a piece of hard fiber on the insulation directly ahead of the top stick and hammer it while the top stick is being driven into place. In many cases this insulating cloth is not cut off and folded over, in which case a separator is placed directly on top of the wires of the bottom coil and another slot slider is inserted on top of the separator. In this case the two slot sliders are trimmed off after the top coil is in place and folded over in the same manner as the top slider before the top stick is driven into 217 28 WINDING ALTERNATING-CURRENT MOTORS place. It is the best practice, however, to fold over the insulation of each coil separately as shown in B and C, Fig. 24. It is advisable to provide additional insulation between two coils of different phases, especially where the voltage of the motor is over 250 volts. There are two ways of providing this additional insulation. One method is to tape one-fourth to one-half of the coils with a layer of half-lapping empire cloth or linen tape in addi- tion to the usual cotton taping. This specially taped coil is used on the first coil of each pole-phase group. Thus if there are two coils in each pole-phase group, one-half of the coils would have this added insulation, while if there are three coils in a pole-phase group, as in the motor under consideration, every third coil should be heavily insulated. The other method of insulating the pole- phase groups is to insert a triangular piece of insulating material under the first coil of each pole-phase group. These triangular pieces of cloth are cut from a square of cloth of such dimensions that the altitude of the triangular piece is equal to the distance from the point of the coil to the edge of the core plus 1 inch. The method of cutting these pieces from squares of cloth is shown in D, Fig. 24. There is a short space between the ends of the slot slider or cell and the taped portion of the coil where the only insulation on the wires is that due to the cotton covering. This portion of the coil is usually insulated by inserting a strip of linotape around the coil sides and see-sawing it back and forth until it is partly under the slot insulation. One end of this tape is then tucked in between the two coil sides and the tape is wrapped around the ends of the coil and the slot insulation several times, thus making the insulation of the coil continuous throughout. The end of this tape is inserted under the last turn and then pulled tightly in position, which will hold it firmly in place. The inside or top leads of the coils are then bent upward and inward and the cotton insulation is removed for about an inch or more. These leads are all connected together with bare copper wire so that the coils can be tested for grounds. A testing trans- former is used in applying the voltage between the windings and the iron case. The voltage to be applied in making the ground test on new windings is "two times the name-plate voltage, plus 218 WINDING ALTERNATING-CURRENT MOTORS 29 1000 volts" and should be held on the windings for one minute. Thus for a 220-volt motor the test voltage would be 220X2+1000, or 1440 volts. Most of the testing transformers will give voltages in steps of 250 or 500 volts so a 1500-volt test should be applied to this motor. In case there is a ground or defective spot in the insulation, current will flow from the windings to the core and blow the fuse in the transformer circuit or open the circuit breaker. When a testing transformer is not available, the windings can be tested by using the highest voltage available. With this method the correct number of lamps should be connected in series with the test leads in order to limit the current flowing through the defective winding. With the lamps in the circuit a defect is indicated by the filament of the lamp becoming bright. The defective coil can be located by dividing the winding into groups and testing each group and then each coil in that group until it is found. Connecting Coils. After all the coils have been inserted in the slots in the stator, the ends insulated, and slot wedges driven in place, the next step is to connect the coils of each pole-phase group in series. The number of coils in each group is equal to the total number of coils in the stator divided by the number of poles and the number of phases. In this case, 36 divided by 4×3 equals 3. Thus there are three coils which will be connected in series with each other in order to form a pole-phase group, Fig. 26. In this figure all of the coils of the stator windings are shown. In con- necting the coils, the outside end or lead of one coil is connected to the inside end or lead of the next coil, the outside end of that coil to the inside of the next, etc., thus connecting the three coils together. The inside end of the first coil and the outside end of the last coil will be used in connecting one pole-phase group to another pole-phase group. In connecting the coils into groups, it is best to start at one place and bend the inside lead of the first coil in toward the center, then bend the outside lead of that coil and the inside lead of the next coil together. The outside lead of the last coil is connected with the inside lead of the next one, and the outside lead of this coil would be bent away from the center, out of the way. This process is repeated for each of the pole-phase groups all around the stator. If an error has been made in dividing 219 30 WINDING ALTERNATING-CURRENT MOTORS the coils into phase groups, it would be discovered and could easily be corrected before the coils have been actually joined together. -- THILD ANTIMEMINE [113] Vanu -⠀⠀⠀⠀NTOS ------ GLU2|13138. EMBRA ------- CHEMIST Sunnu ***I <}}}|||||||!! 11111 · HEITIMMTETIZIA MELANIEM Gu……|||||||| -----ONLI 15132:410531INILAD, REPTILIENMEDEN ------ Su R000 ZAPEELTEMARIO PISANORIALS Jung ANEMIES } ▬ : Q Q -----* ■ - 120 #CI ww GARANTIIMIINI MESTRIMLESSIN MOREMIUMALITY Marissen KIMRHUND KMALEUN PREJ TTL EPSON DU 23 23 ED BOL CHINIUM HU ISO ČOR MLITA ici APETHIEMELTETILENSUULUIS) (NEMASHITINt ........ SUMMUMBUMASIKIKA?? KASETME13AZIPEDIITTIMANANTINY ZITIÚINNMUHUIIIIIIN #1212474) ---- IMMINUMTESIUMujaki?? 1 ------- # mi Fig. 26. Method of connecting stator coils into groups. The next step is to remove the surplus insulation, such as the cotton covering and sleeving, from that portion of the wires that will be twisted together in connecting one coil to the next. If the copper wire is tarnished or enameled, it must be polished with sandpaper and then tinned. The process is repeated for all the leads that are used in connecting the coils into phase groups. The bared ends of the two leads are then gripped with a pair of pliers and twisted together as shown in Fig. 27. The length of the twisted portion should be about an inch, and each wire should make at least two turns about the other one. After the ends are twisted together, the winding should be checked to see that the proper number of coils have been connected together. The twisted ends. are then coated with a soldering flux and soldered either with an iron or by using a small ladle and dipping the terminals in the molten solder or pouring it over them. It is best to use a rosin flux in soldering. If an acid flux is used and any of the flux is left on the wire, it will collect moisture, which will corrode the copper wire and in time will injure the insula- tion. A good soldering flux which is not corrosive can be made by mixing one part glycerine, four parts alcohol, and five parts satu- rated solution of zinc chloride. A flux which gives good results can also be made by dissolving rosin in benzine, but it is more difficult to solder with this flux than with the zinc chloride mixture. 220 WINDING ALTERNATING-CURRENT MOTORS 31 4 The ends of the wires are next cut off so that the soldered ends or stubs will be about to 1 inch in length. These stubs are insu- lated by wrapping them with friction or linen tape. A better and a neater job can be produced if the tape is cut into - to -inch 3 LEADS @ 01 I nimus. LEADS ENDS OF WIRE BRAIDED COTTON SLEEVING EXTENDS TO HERE Fig. 27. Method of connecting coils into pole-phase groups. widths instead of the standard 2-inch width. At the present time, flexible varnished cambric tubing or sleeving is being used quite extensively instead of tape in insulating the stubs. This sleeving is easily slipped over the stub ends of the wires and when in place is cut off about one-fourth of an inch beyond the ends of the stubs. When the distance to the bearing brackets or frame of the machine is small, the insulated stubs are then bent inward between the coils so that they will not come in contact with the frame when the stator is assembled in the machine. When there is sufficient clear- ance, they do not need to be bent inward. Connecting Pole-Phase Groups. The next step is to connect the different pole-phase groups together. The groups of coils of one phase can be connected so they are all in series, all in parallel, or a combination of series and parallel groupings, depending entirely upon the number of pole-phase groups in each machine. In the particular motor that we have been considering, the coils are all connected in series, as will be noted by referring to the data sheet which states, "series Y connection." One of the groups of coils near to the place in the frame where the external leads will be brought outside can be considered as phase A. The outside lead 221 322 WINDING ALTERNATING-CURRENT MOTORS ! from this group will be connected to the outside lead of the next phase-A group, and the inside end or lead of this group to the inside end of the next group-and so on around the armature, Fig. 26. NEUTRAL A' Lo 14 15 13 16 12 17 a man and aut !!! 18 'C' 10 9 360 *-120º. 2 B' L ·120° ·120° ∞ 7 A 6 5 A CONNECT_A', B, C' TOGETHER FOR Y OR STAR CONNECT A'B, B'C, C'A TOGETHER FOR DELTA Fig. 28. Standard diagram for a 6-pole, three-phase, Y or Delta stator. B A standard conventional diagram for this machine is shown in Fig. 28. The coils of the phase-B group, next to the phase-A group, are not connected at this time. The coils of the phase-C group, beyond the phase-B group, are next connected in the same manner as the coils of the phase-A group. Then the phase-B group can be connected in like manner beginning with the group which is to the right of the phase-C group that was connected. It will be seen in Fig. 28 that the group of phase-B coils between those 222 WINDING ALTERNATING-CURRENT MOTORS 33 connected to the external A and C' leads is not used as the beginning of that phase winding but as the ending. This is because there are 120 electrical degrees between each of the phases, as shown in the volt- age wave in Fig. 4. In an alternating-current motor or generator the electrical distance from the center of one pole-phase group to the third pole-phase group of the same phase is 360 electrical degrees, Fig. 28. In A, Fig. 29, the different phases are repre- sented by the lines AA', BB', and CC', and the A', B', and C' ends of the phases are connected together at a point called the neutral, thus forming a Y connection. IA IC NEUTRAL 0 · 120º, -1209 VAI B' -120°- B' B A Fig. 29. Graphic representation of winding of a three-phase motor. الدورة d B you In case the phase-B external lead had been connected to the phase winding between the leads of phases A and C of Fig. 28, the resulting connection would be that indicated in B, Fig. 29. Thus will see, referring to this figure, that there are only 60 electrical degrees between phases A and B and B and C. An induction motor connected in this manner would not operate satisfactorily and would soon overheat. In connecting B- and C-phase groups of coils of a three-phase motor, it is a good rule to remember to pass one phase group and start on the third and the fifth phase groups as a beginning for phases C and B. The mistake of con- necting the winding in a reverse manner is frequently made even by experienced armature winders. In making the connection from one phase group to another, it is not advisable to use cotton-covered wire, but rubber-covered or slow- 223 34 WINDING ALTERNATING-CURRENT MOTORS burning insulated wire of the next size larger than that used in the coils. The reason for the use of a larger size is because the heat is not radiated as fast from the rubber-covered wire as from the cotton- covered wire. When there are a number of coils connected in parallel, as will be noted by the diagrams given in the section on "Standard Induction Motor Diagrams," it is well to run four copper rings of insulated wire around the stator and tape the coil groupings to these rings. The cross-section area of the wire used in these rings should be equal to the area of the wire in the winding multiplied by one-half the number of coils connected in parallel. Thus on a 6-pole, three- phase motor where there are six groups connected in parallel, the size of the wires for the ring should be three times that of the wire used in the coil. If No. 20 wire, which has an area of 1022 circular mils, is used in the coil, it will be necessary to use No. 15 wire, which has an area of 3255 circular mils, in the ring. After the coil groups have been connected together, soldered, and taped, and the external leads connected to the winding, the wires used in making these connections are tied securely in place with twine or cord so that they will not be injured or become caught in the revolving parts of the machine. WINDING ALTERNATING-CURRENT GENERATORS Small Generators. The general appearance of a small, alternat- ing-current generator is very similar to that of a direct-current machine. The electrical connections, however, are different in that the commutator is replaced with collector rings. On a single-phase machine two collector rings are necessary; on a two-phase machine four rings are required; and on a three-phase generator three rings are used. The field coils are constructed in the same manner as for direct-current generators and there is very little difference in the mechanical construction of the frame and armature. Frequently the manufacturer uses the same armature and field punchings for an alternating-current machine that was used with the direct-current machine. The armature coils are insulated before being placed in the slots in the same manner as described in the section on "Winding Direct- Current Armatures." Instead of connecting each coil to a commuta- tor bar, the coils are divided into phase groups in the same manner as 224 WINDING ALTERNATING-CURRENT MOTORS 35 for the stator of an induction motor. These different pole-phase groups are connected in a manner similar to those on induction motors. The windings on the armature are connected either Star or Delta, and the leads that were brought outside of the frame of the induction. motor correspond to the leads in the armature which are connected to the collector rings. In connecting the different pole-phase groups together on the armature, it is necessary to make these connections more secure and tie the connectors more securely in place than in the induction-motor stator, because centrifugal force will tend to throw the coils outward and wreck the armature windings. When the capacity is less than 5 horsepower, it is sometimes advisable to make the machine produce both direct and alternating current. The direct current is used for exciting the fields of the generator, which then becomes a self-excited or self-contained machine. In this case the collector rings are usually mounted on the opposite end from the commutator, and a connection is made from the collector rings to the correct points in the armature winding. In a three-phase generator the leads would be connected to points that are 120 electrical degrees apart. The majority of machines using this type of construction are either 2- or 4-pole, and the alternating cur- rent leads are connected to points that are one-third or one-sixth of the circumference of the armature. Thus with a 4-pole machine. having 60 armature coils, one collector ring would be connected to armature coil No. 1, the next ring to coil No. 11, and the third ring to coil No. 21. Large Generators. In alternating-current generators of a capacity greater than 25 to 50 kv.-a., the armature winding is placed on the stationary part of the machine the same as in an induction motor, and the field coils are placed on the revolving part called the rotor. The advantage of this is that the field coils instead of the armature coils are subjected to centrifugal force which tends to throw them out of place. It is easier and cheaper to make the field coils. withstand this force than the armature coils. The armature coils and connections can be secured firmly in place on the stator much easier and cheaper than when they are placed on the revolving part of the machine. In these generators the slots are of the open type and the coils are usually insulated thoroughly by special processes before being inserted in the slots. The reason for this is because 225 36 WINDING ALTERNATING-CURRENT MOTORS these machines are usually operated at much higher voltage than the other machines described in this section. Special instructions, drawings, and diagrams showing how the coils are to be constructed, insulated, and connected are usually furnished by the Engineering Department to the shop for each particular machine. Happy ネット ​INSTALLING THE ARMATURE COILS IN A 7,500 KVA SYNCHRONOUS CONDENSER, 13,200 VOLTS Courtesy of Westinghouse Electric & Manufacturing Co., East Pittsburgh, Pa. 226 REPAIRING ALTERNATING- CURRENT MOTORS AND GENERATORS Introduction. The first part of this section will take up the subject of testing the windings and the latter part will deal with repairing, rewinding, and reconnecting the windings of motors and generators. It is very fitting that the subject of testing windings should be located between those describing the winding of new machines and the repairing of old ones, because with a new machine it is about the last operation, while in repairing an old one it is the first. It is essential that a new winding be properly tested in order to locate all defects before the motor is placed in service. The little defects can be easily removed at this time before they have a chance to damage the whole winding. It is a good practice to check and test the winding after every operation, or when each person finishes his work on the winding, for then the responsibility can be placed where it should be. The manufacturers of electric motors usually have a regular schedule of tests that must be made on the windings during each step in their construction so that they will function properly in service. In order that these tests can be made quickly and easily, it is necessary to provide special testing equipment. It is impossible for the repair man or small shop to provide the same testing equipment that the large manufacturer uses because the expense would be too great in proportion to the work done. How- ever, there is some equipment that the repair man can build during spare time from junk materials which accumulate in the shop. TESTING THE WINDINGS The defects in the windings of alternating-current motors and generators can usually be grouped under five headings which are given in the order in which the greatest number occur: grounds; short-circuited coils; reversed connections; open circuits; and wrong connections. The methods described for testing and locating the 227 2 REPAIRING ALTERNATING-CURRENT MOTORS defects will apply both to a new machine that is built by the manu- facturer and to repairs that are made on an old winding in the repair shop. Grounds. The testing of the windings for grounds is done by connecting one terminal of a testing transformer to the windings and the other terminal to the frame of the machine. The test voltage applied to a new winding is usually twice the rated voltage of the machine plus 1000 volts. The test is applied for one minute. When there is considerable testing to be done, the time is shortened to one or two seconds and the test voltage is made 1.2 times that for one minute. The winding of a machine that has been in service for some time will not be able to stand the above voltage test. The test voltage for these machines should be twice the rated operating voltage. However, if several coils or part of the winding is replaced with new coils, this portion should be tested when inserted in the slots at the higher voltage, but after it is connected to the old wind- ing, the test voltage should only be twice the operating voltage. The windings should be tested for grounds as soon as the coils are inserted in the slots, the insulation folded over, and the slot wedges driven into place. Take a piece of bare copper wire and connect all the leads of the coils together so that they can be at- tached to one of the leads of the testing transformer. The other lead of the transformer is connected to the core or frame. If a ground exists, current will flow through the frame and winding from the secondary winding of the transformer. A fuse or a small circuit- breaker is located on the primary side of the transformer and this fuse or breaker will open the circuit when a ground exists between the frame and winding of the motor being tested. The ground can usually be located by seeing a flash or small arc between the winding or core, or by a small puff of smoke, which is the result of a burned insulation. When the defects cannot be located by the above methods, the windings that are connected together by the bare copper wire should be divided into two groups and each group tested. The group that has the defect in it is divided. into two more groups and tested again. This process of dividing the defective coils into two groups is continued until the defect is located. This method is the quickest and surest because in case there are two or more defects they will be discovered. 228 REPAIRING ALTERNATING-CURRENT MOTORS 3 The majority of the defects due to the grounding of the wind- ings of an induction motor occur at the edge of the core. This is often caused by bending or forcing the winding down over the end of the core at the end of the slot. The sharp edge of the end lamina- tion of the core cuts through the insulation and allows the copper wires in the winding to touch the iron of the core. The slot wedge of this slot and one or two slots on either side of the defective coil should be removed so that the defective coil can be lifted or raised out of the slot for repairs. When a portion of the coil inside the core is not taped or insulated before being placed in the slot, as is often the case with partially closed slots, the defect can be repaired by inserting additional insulating material between the core and winding. This additional insulation should be of such size that it will extend at least an inch beyond the burned spot on the original insulation. The wire of the coil, where the ground occurs, should be examined to see that the arc produced between it and the core by the testing transformer did not injure the wire or reduce its cross- sectional area. If the wire is burned or melted away at this point enough to reduce the area to three-quarters of the area of that size wire or conductor, the coil should be replaced with a new coil. If this is not done, the wire will overheat at that point and in a short time the insulation will burn and the winding will either be grounded or a short circuit will be formed between several turns of the coil. These few turns will heat very rapidly and if the motor is operated for any length of time in this condition, the whole motor winding will burn up. When a ground occurs on a coil that has been taped or treated before being placed in the slots, it is best to either remove the coil or to raise up that side so that the burned insulation can be removed and the portion of the coil retaped and insulated or treated with insulating varnish. The burned spot should be examined to see that the arc between the wires and core did not injure the insu- lation between adjacent turns. If it appears that the insulation between turns is injured, it should be strengthened by inserting small pieces of treated or varnished cloth between the adjacent turns. The windings of the machine are tested again for grounds after the coils have been connected together in the proper manner. The final ground test is made after the machine has been completely : 229 4 REPAIRING ALTERNATING-CURRENT MOTORS assembled and given a shop or heat test. It is seldom that a ground will show up on the later tests unless the winding is injured in the shop or during assembly, especially if any defects that developed and appeared on the first test are properly repaired. Testing Transformer. The transformer used for applying a voltage test to the windings in order to locate grounds can be pur- chased from a manufacturer of transformers, or it can be built when the necessary materials are available in the shop. A small 500-watt bench type is very handy for the armature winder and repair man as it can be easily carried from one place to another and set on the bench near the work. When there is only one transformer in the plant or shop, it should be of a larger size, usually of a one- or two- kilowatt capacity. The dimension and construction of the core for a one-kilowatt transformer is shown in Fig. 1. The transformer core is composed of a No. 26 U.S. gage (0.019 inch) sheet steel of the same quality as is used in the cores of armatures. The sheet steel is cut into strips that are 11 and 17 inches long and 2 inches wide. Half of these strips are dipped into thin insulating varnish and dried before assembling in a core. When the core is assembled or stacked, a layer of the laminations are arranged as in A, Fig. 1, and the next layer with the varnished strips are arranged as in B. The next layer, which is not varnished, is arranged as in A, and this process of arranging the layers and having every other one varnished is continued until the core is completed. The reason for arranging the laminations as shown in A and B is to break the joints and form a solid core that will allow the magnetic lines of force to pass through it easily. The purpose of using the varnished strips is to keep the laminations from making metal contact and thus prevent any electrical current from flowing from one lamination to another. These electrical currents are usually called eddy currents. The core is clamped by the pieces of angle iron and bolts, as in C and D, Fig. 1. A piece of pressboard or fiber is inserted between the core and the angle iron braces. They are put on after the coils are in place. The sides of the core where the coils are located are taped with half-lap cotton webbing or tape, which is wrapped on as tight as possible in order to hold the laminations in place when the coil is being wound on the core. The clamps and the laminations 230 REPAIRING ALTERNATING-CURRENT MOTORS сл 5 17". i 2" C BOLT 4" LONG -3" -2"*- PLUG DETAIL OF TERMINAL BOARD 9H |~—-5″- A - |" → 8/2 FIBER -- 17" x 2" D 4-PIECES ANGLE IRON 2"x2"x16" -3" -3″ —— -⇒ TERMINAL BOARD 0 250 2 500 3 11" x 2" 500 4 1000 (5 250 (6) B O LAMP 15". RED 1 TAPE F חד A m 6 3 4 5 CIRCUIT BREAKER HIGH TENSION CABLE Fig. 1. Details of Testing Transformer FUSE этт lleges BEGINNING / END B ENDING END E с oooooo COIL NO. I COIL NO.I relllllll COIL NO. 2 00000000000000 еееее PRIMARY WINDING COIL NO.2 SECONDARY WINDING A SWITCH -> B 110-VOLT LINE 231 6 REPAIRING ALTERNATING-CURRENT MOTORS under the clamps are removed in order that the taped core can be fastened in a lathe or winding machine and the coils can be wound on the core. The core is insulated with one layer of 0.030-inch pressboard, one layer of 0.010-inch flexible mica or empire cloth, and one layer of 0.020-inch horn fiber. The material should be arranged so that joints of the different layers do not come opposite each other, but each sheet will go around about one and one-quarter times. The electrical data for the winding of the transformer is given below. Primary voltage. Number of turns. • Number of turns per coil. Size of wire.. Coil composed of. • • Secondary voltage... Number of turns.. Number of turns per coil. Size of wire.. • PRIMARY WINDING SECONDARY WINDING + • 110 .516 .258 .No. 8 D. C. C. .3 layers of 86 wires each Coil No. 1 composed of 2346 turns, 6 layers of 391 turns to tap No. 3. Coil No. 1 composed of 4692 turns, 12 layers of 391 turns to tap No. 2. Coil No. 1 composed of 5870 turns, 15 layers of 391 turns to tap No. 1. Coil No. 2 composed of 4692 turns, 12 layers of 391 turns to tap No. 5. Coil No. 2 composed of 5870 turns, 15 layers of 391 turns to tap No. 6. 250 to 2500 11740 5870 .No. 23 D. C. C. The same amount and kind of insulation should be used between the primary and secondary windings as was used between the core and primary windings. One layer of 0.010-inch empire cloth should be placed between each layer of wires on both the primary and secondary coils. The leads for the terminals and taps of the second- ary coils should consist of No. 12 or 14 lamp cord soldered to the solid wire in the coil. The lamp cord, being composed of a large number of small wires, is very flexible and can be bent without danger of breaking. The two primary coils are connected in series by connecting the leads B and C together as shown in E and F, Fig. 1. All the coils are wound in the same direction and the leads and taps of the secondary coils are connected as shown in the wiring diagram. The connections are made as shown in the detail on the back of the terminal board. The leads marked 1, 2, 3, etc. are connected to the 232 REPAIRING ALTERNATING-CURRENT MOTORS 7 corresponding numbered terminals on the back of the board. Con- necting the terminals on the back of the panel provides a safe installa- tion for they cannot come in contact with the high-tension wiring. The two testing leads that connect to the plugs which fit in the terminal board are 10 to 15 feet in length and are composed of high- tension rubber-covered wire such as is used in wiring spark plugs on an automobile. The numbers between the holes on the ter- minal board in F, Fig. 1, indicate the voltage that exists between them. When it is desired to obtain 250 volts, the plugs can be inserted in holes 1 and 2 or 5 and 6. Likewise, for 1500 volts, the plugs are inserted in holes 3 and 5; for 2500 volts, the plugs are inserted in holes 1 and 6. The transformer, terminal board, circuit breaker, and switch can be mounted in and on a box that can be pushed from one place to another. The red lamp, which is connected across the terminals of the primary winding, should be mounted on top of the box so that those working about the transformer will know that it is in use. The circuit breaker will open the circuit when a defect develops in the apparatus being tested. It can be closed much more quickly than a fuse can be replaced. The fuses at the switch are for pro- tection in case the circuit breaker fails to operate. In installations where the transformer is not used very often, a renewable fuse may be used in place of the circuit breaker. Short Circuits. A short circuit is caused by two wires coming in contact with each other, providing a shorter path having lower resistance than the designed path. The current through any short circuit can be found by applying Ohm's law, which states that the current is equal to the voltage divided by the resistance. When two copper wires come in contact with each other, the contact resistance will be very low, usually less than 0.01 ohm. If the voltage pro- duced by the coil, or turn, that is shorted is only one volt, the current that will flow through is 1÷0.01, or 100. This is a very large current for the usual size of wire used in medium sized motors. This current will soon heat the wire to a temperature which will melt the insulat- ing compound out of the windings. If the machine is not stopped at once, the insulating material will be burned. When one of the turns on the coil comes into contact with another turn and forms a short circuit, Fig. 2, the current supplied 233 8 REPAIRING ALTERNATING-CURRENT MOTORS to the motor from the line does not flow through all the turns, but a part flows through the short circuit to the next turn or coil. This short-circuited turn is an idle coil, which acts as a generator and produces voltage, because it is cut by the lines of force produced by the rotating magnetic field. The current will enter the short-circuited coil at A, Fig. 2, and flow through the sides of the coil numbered 1, 11, and 2, through the spot where the bare wires touch each other, as at X, through 13 and out of the coil at B as shown by the heavy arrows. A voltage is produced in the coil sides 3 and 12, due to the magnetic lines of force in the iron changing as the current flowing from A to B changes in different parts of the cycle. This voltage causes a current to INSULATED WIRE -12. +13 12 BARE WIRE 2 2+ 34- Fig. 2. A Short-Circuited Stator Coil 3 flow through conductors 3, X, and 12, and back to conductor 3, as indicated by the dotted arrows, Fig. 2. The current in this coil can easily be from two to ten times stronger than the current flowing through the rest of the coil. The result is that the wire becomes very hot in a short time. There are several methods that can be used to locate a coil that has one, several, or all of its turns short circuited. The greater the number of short-circuited turns in a coil, the sooner it will heat and make itself known. When the stator winding is assembled in the motor, it can be tested by running the motor without any load for from ten to thirty minutes and observing the temperature of the ends of the coils with the hand as soon as the motor is stopped. The temperature of all the coils should be the same. If one or two of the 234 REPAIRING ALTERNATING-CURRENT MOTORS 9 coils are much warmer than the others, it would indicate that they are short circuited. A short-circuited coil can be located in the stator winding by using the growler in the same way as on direct-current armatures. श्र T 1 P DRILL "HOLE B 7100 3-LAYERS HARD FIBER Ά 42 4½" · 28 · A 3/16 HARD FIBER → "1 2"- < -3″R= *•. |". inle THIS SECTION IS CUT OUT SO FIBER CAN SLIP OVER CORE AND IS THEN GLUED IN PLACE. S 6½" -21" CORE 319 #1 / 2½" "RIVETS A G с 20 * The 100 2" 2-PIECES 3/16" HARD FIBER Fig. 3. Details of Growler for Testing Stator Coils *** ミ ​p STEEL WASHERS 62/2/2 -HARD FIBER TAPE The shape of the growler should be convex, Fig. 3, instead of concave. The radius of the curvature of the growler should be about the same as the inside of the stator laminations. The other side of the growler can be made to a different radius so that it can be used on another 235 10 REPAIRING ALTERNATING-CURRENT MOTORS size stator. The amount of current required to operate a growler is reduced considerable when the contact surface, or area, of the growler that is in contact with the stator laminations is increased. The reason for this is that iron is a better conductor of the magnetic lines of force than air. The current required to operate the growler can be decreased by winding more turns on the coil, but this also reduces its ability to detect a short-circuited coil. Constructing Growler. The growler, Fig. 3, is constructed from sheet metal laminations that are cut to 4½ by 5 inches, as indicated by the dotted lines, and stacked in a pile. Three-sixteenths inch holes are drilled for the rivets. There should be enough of the laminations so that they will make a pile 2½ inches high when they are clamped tightly together and riveted. The laminations should be clamped by hand or by a hydraulic press when available in order to obtain a solid and well-built growler. Another method is to use a wooden or steel beam or bench vice for clamping the laminations while they are being riveted. A steel washer should be placed on each end of the rivet in order to secure greater bearing surface on the laminations. Cut the space for the coil and round off the edges of the laminations to the radius shown at A, Fig. 3. This can be done with a hack saw and the sharp corners smoothed up with a fine file. The edges of the core, where the coil is located, are rounded off so that they will not cut through the winding and cause a short circuit in the coil. A strip of 0.007- to 0.010-inch flexible horn fiber or fish paper is wound three times around the core of the growler. The two pieces of 1-inch hard fiber shown at B, Fig. 3, which insulate and support the sides of the coil, are placed in position as shown at A. It is necessary to cut out a section of the fiber in order to place it on the core, and this piece should be glued in place and can be made stronger by glueing a piece of 32-inch horn fiber to the outside of the 16-inch fiber after it is in place. The growler should be wound with about 250 turns of No. 16 double-cotton covered wire when it is to be operated from a 110- volt alternating-current circuit. A piece of No. 14 rubber-covered wire with stranded conductors should be soldered to the end of the No. 16 cotton-covered wire, because it is more flexible and not as easily broken as a solid wire. This rubber-covered wire should form the first turn on the core of the growler. In winding the coil, it is 236 REPAIRING ALTERNATING-CURRENT MOTORS 11 desirable to insert a layer of paper or empire cloth between every four or five turns in order to improve the insulation on the coil. When the desired number of turns have been wound on the growler, a piece of the rubber-covered wire is soldered to it to form the ex- ternal lead. The coil is dipped or painted with insulating varnish а D оо о ООС A SHEET IRON FIBER SLOT WEDGE SLOT INSULATION MAGNETIC LINES OF FORCE ос ооо Оос OOO OOOO Fig. 4. Method of Using Growler SHEET IRON B or compound, and then cotton or friction tape is wound tightly over the core in the same direction as the wire to protect it from injury. Action of Growler. When the growler is placed over a coil in the stator, Fig. 4, and the current turned on, a voltage is induced in the coils in the slots due to magnetic lines of force passing from one 237 12 REPAIRING ALTERNATING-CURRENT MOTORS side of the growler to the stator teeth, through the coils in the slot to the teeth on the other side of the slot, and into the growler. The action of a growler is the same as that of a transformer. If the windings of the stator are free from short circuits, there will not be any current flowing through these windings because the circuit is open. If, however, the winding has a short-circuited turn, or coil, in it, a current can flow through this turn, or coil, because there is a complete electrical circuit. The amount of current flowing will depend on the voltage induced by the growler and upon the resistance of the circuit. The current flowing in the short-circuited coils pro- duces magnetism or lines of force which oppose those produced by the growler. This opposition causes the growler to take more current, which would be observed if an ammeter was connected in the circuit. Thus an ammeter could be used to detect a short- circuited coil. It is not necessary to go to the expense of using an ammeter because the short-circuited coil can be easily located by passing a small piece of sheet iron or steel over the slots in which the other side of the coil, that is under the growler, is located, Fig. 3. If there is a short circuit in that coil, the piece of sheet iron will be attracted to the stator core at a point directly over the short-circuited coil. This is due to magnetic lines of force being set up around the coil, as shown at A, Fig. 4. These lines of force pass from one tooth, through the core, to the tooth on the other side of the coil, and then through the air to the first tooth. A piece of sheet iron, or steel, will easily provide a better path than air, and the lines of force will tend to pass through this piece of iron or steel, as shown at B, Fig. 4. This causes the piece of steel to be drawn to the core. When there is one side of two coils in the same slot, as is often the case on most induction motors, a piece of sheet steel should be passed around the core on both sides of the growler. The growler should then be moved so that it will be over the next coils and the core again tested with the piece of iron. This process is kept up until the growler has been over all the coils and the opposite side of the coil has been tested. The growler is very useful in locating short circuits in a coil or in locating a complete short-circuited coil. It is not as good in locating a complete short-circuited pole-phase group, because it 238 REPAIRING ALTERNATING-CURRENT MOTORS 13 · does not induce a high enough voltage to cause a current to flow through the pole-phase group and produce enough magnetism that will attract a small piece of sheet iron. If the growler was strong enough to attract the piece of iron, there would be an attraction over all the sides of the coils in that pole-phase group. A short- circuited pole-phase group is usually caused by a mistake in con- necting the windings and is very easily detected when the winding is tested for reversed coils with a compass. The same is true when one phase is completely short-circuited due to wrong connection. Reversed Connections. Reversed connections in the winding may be caused by a reversed coil, a reversed pole-phase group, or a complete reversed phase. These defects can sometimes be located by a careful inspection and checking of the connections, but it is better to test the windings and locate the defect with a compass. Compass Test. The compass test will locate a reversed coil, a reversed pole-phase group, a reversed phase, a short-circuited pole- phase group, and a short-circuited phase. It is necessary to use direct current for this test, because with alternating current the direction of flow changes so rapidly that the compass needle cannot follow the changes. If there is a source of direct current in the shop, all the equipment needed will be a rheostat, which will limit the current to a safe value, and an ordinary pocket compass. When direct current is not available, an ordinary 6-volt automobile battery can be used. A rheostat will not be needed with a battery because the current can be regulated by increasing or decreasing the 1. aber of cells used. It is necessary to use only enough current to strongly attract the compass needle to the core. The majority of machines built today are three-phase and their windings may be either star- or delta-connected. In making this test, the three external leads from the motor are marked or designated A, B, and C, or they can be marked I, II, and III with chalk, or a small notch can be cut in the insulation of the wire on the lead near the end that is not connected to the windings. Likewise, one of the direct-current leads should be marked and considered positive. This lead is attached to the A lead of the stator winding and the other direct-current lead is attached to the B lead. Current will now flow through the windings of A-phase and B-phase, as shown by the arrows, Fig. 5, which is a complete winding diagram for a 3-phase 239 14 REPAIRING ALTERNATING-CURRENT MOTORS 4-pole series star-, or Y-connected, machine having 36 slots and 36 coils. The polarity of the poles, as indicated by the compass, is shown by the heavy letters S and N, which are near the bottom of the core. This polarity should be marked on the core with chalk. The two direct-current leads are removed and the positive, or marked, lead is connected to the B-lead of the machine and the A STATE AND core. - - all b DIRECT CURRENT - (in farben) Tema……… quum ABUNZI: -- MIN ||||||||||||MINIZA Summ ----.... 101] & sumummimimiimiiting? : { other direct-current lead is connected to the C-lead. Current is passed through the windings and the polarity, as indicated by the compass, is marked on the center of the core in the same manner as before. The leads are disconnected and the marked, or positive, Fig. 5. Magnetic Polarity of a Correctly Connected Stator /!ווומון!! Z C B ស A2 B ILIZER 11111 ms m QUINS JUTERII: ------=|=| ESTHE ZUMBA:::::::: TODA More on c……………………………………………………s LUMISHI BULG ic JOBMZIZISI. * 1 … . . . Ramune F÷U=U 20:0 === E! S -- COMMENTARIS --- # 8 (SOURCETERIJA) E GIAN MATE 2-**** MUUNA FUSEUM SUMMUMINUMƏ RUBICI JEUSBER OUR 10 DAN MEN VAN DE DAT GLITEH YcY FE MINIMILA AMITHIUME SPUTNITE HE SELARE DIE SIE TIME IIIES MATTHE GTERSELFLATTOPP FELIPART Summ Fig. 6. Magnetic Polarity with a Reversed Pole-Phase Group of Coils lead is connected to the C-lead and the other direct-current lead is connected to the A-lead. The polarity is marked at the top of the The polarity marks on the core will resemble Fig. 5 and will be N, S, N, S, etc., on around the winding. This indicates the correct 240 REPAIRING ALTERNATING-CURRENT MOTORS 15 polarity and shows that the winding has been correctly connected. The polarity would be the same for a delta-connected winding as for a star connection. When the polarity of the windings, shown in Fig. 6, are tested by passing current through them, it is observed that the polarity of the three phases are S, N, S, S, S, N, S, N, S, N, S, and N. It is seen at a glance that one of the pole-phase group of coils is reversed because there are three south poles together. In order to determine in which phase the reversed group is, the polarity of each phase should be observed. Thus for phase A, the polarity is S, S, S, and N, which indicates that the second pole-phase group is the one that is reversed. If the polarity of the second pole-phase group is changed by reversing, the connections of this group would read S, N, S, and N, which is correct. Comparing the connections of the winding in ………… CUHUN ## 200 ساط A G||||||||||NIT # AH…………………………… 11111 MUS mu« C ROMANUS BAD! 三國​法國​公雞 ​-- vumm 40013|||||||||||||| B AM……⠀⠀⠀ ---- HITEFOR? -={ mu:: 1891/9 3011011 #30=0 L MATTHEEUU MUN MUS Call G2018|||||||| #11 mult | 20 10 -> BE (0) - --- ***…………… CIVE- S m ... MAWSUI SKEN$L. N Fig. 7. Magnetic Polarity with a Reversed Coil W - # #111111 SIMIA CASTER ------- VAIKINU ………2 Fig. 6 with the correct diagram in Fig. 5, it is seen that the second pole-phase group of phase A is the one that is not correctly connected. The correction can be made by connecting al to A2 and a2 to 43. In testing the winding, Fig. 6, one test lead is connected to the neutral, while the other lead is connected first to A-phase, then B-phase, and then to C-phase. The connections can be made as in Fig. 5 if desired and the result and polarity will be the same. It is not as easy to locate a reversed coil in a phase group by the compass test as it is to locate a reversed pole-phase group. The direction of the flow of current through the windings, when there is a reversed coil in the third pole-phase group of phase 4, is shown in Fig. 7 when direct current is being passed to the A lead of phase 241 16 REPAIRING ALTERNATING-CURRENT MOTORS A, and the compass is slowly passed over the stator core, the needle will gradually change from south to north, then slowly to south, etc. The direction that the compass needle points when held over slotṣ numbers 10 to 23 is indicated by the short arrows above the slots, Fig. 8. The dotted lines and the arrows indicate the direction of flow of the magnetic lines of force produced by the direct current in the winding of phase A. In Fig. 8, which is an end view of the windings in the slots, the compass needle points horizontally when above slot 11, and it gradually assumes a vertical position when it is passed over slot 14, which is a north pole. It attains a horizontal position at slot 17 and changes rapidly to a downward position -12- S+ UGBUUUUUUB UNI 14 22 23 --16- -17 -18 Z+ 24 25 N 26 6)+ $ Fig. 8. Direction of Magnetic Lines of Force Produced by a Reversed Coil -29- between slots 19 and 20 and then rapidly reverses and points upward between slots 20 and 21. As the compass is passed on over slots 21 and 22, the needle changes from a vertical position to a horizontal and then down when it passes over slot 23. The rapid change of the needle as the compass is passed over slots 19, 20, and 21 indi- cates that there is a reversed coil and the connections of the coils of this particular winding in these slots should be inspected closely. This indicates that the coil of phase A winding in slot 20 is reversed. This coil should be reconnected so that the compass needle will change gradually as from slots 11 to 17. This same condition of the compass needle will be observed when it is passed over slots 25, 26, and 27, as when it is passed over 19, 20, and 21, because the other side of the coil is located in these slots. When there are only two coils in each pole-phase group, the effect of a reversed coil would be more noticeable than when there are three, four, or more coils. This condition is more easily discovered with a small direct current than with a very heavy current. A very heavy current will produce more magnetism than can be carried by the core and these lines of force pass through the air and affect the compass when it is held some distance from the core. The magnetism from the reversed coil does not pass out into the air as far as that 242 REPAIRING ALTERNATING-CURRENT MOTORS 17 from the other coils, so the compass is affected almost entirely by the good coils. Reversed Phase. A reversed phase in a three-phase winding can be detected by the compass test. With a reversed phase, the polarity would be S, S, S, N, N, N, S, S, S, N, N, and N, Fig. 9. This shows that the middle one of the pole-phase groups has the reversed polarity because the polarity of a correct winding would be S, N,, S, N, etc. as shown in the preceding tests. With the Y-, or star- connected winding, this error, or defect, is remedied by disconnect- ing the end of the second or B-phase from the neutral connection and connecting an external lead to this end of the phase winding. HIL -- • Wtfl|| MUNUE MAILISUU 0205025 1 B AHHHUNT 6. US FOR HON HAR E MAJIMUMMIZA SUMMUMKI «MIL*********|/||||||||||18 ZIMU::: B MIHENI **********THIN? Hınısı-R-- J -JOKUYU | 22: MI Y5-00 *Bal HEMY ma 打散 ​____ SHI ----. HUMIG MIANMINAIS T PanuHLITIES AIRP GAL:******!! **C# HUBHER mu YcY ISUKIŞI a EXC SCBKEN ELE Fig. 9. Magnetic Polarity with a Reversed Phase FRUITE ISEME SIRINKI HID S The other end of the phase winding would be connected to the neutral connection. In a delta-connected winding, this defect is repaired by disconnecting the ends of the reversed phase and con- necting the opposite ends to the other two phases. A reversed phase connection on a two-phase winding would cause the motor to run in the opposite direction. The rotation of the motor can be easily reversed by interchanging or reversing the two leads of any one of the phases. A reversed phase can be easily discovered when the motor is running without a load, because it will run at a much lower speed (if it runs at all), emits a loud growling noise, and will soon become very hot. This defect can also be detected with the same apparatus used in determining if the three phases are balanced. Balance Test. The balance test determines if there are the same number of coils in each phase. This test can be made with an 243 18 REPAIRING ALTERNATING-CURRENT MOTORS alternating-current ammeter. The alternating current must have a voltage about one-fifth the rated voltage of the motor. With a star- connected winding, one lead of the low-voltage alternating-current circuit is connected to the neutral point and the other lead of the low-voltage circuit is connected to one of the phases. The ammeter is connected to one of the leads and the current taken by the different phases is obtained by changing the low-voltage lead from one phase to another phase. The ammeter should read the same in all three phases. With a delta-connected winding, it is necessary to open up the connections at one of the corners of the delta and connect the low-voltage leads to the end of the windings of each phase. The current taken by each phase is obtained by changing the con- nections from the ends of one phase to the next. A "balance-coil" tester can be very easily constructed with the materials usually found in the average repair shop and can be used in place of the ammeter, Fig. 10. The materials required are No. 22 soft iron wire and No. 18 double-cotton enamel-covered wire. The No. 22 wire is straightened and cut into lengths 14 inches long and assembled into a core until the diameter is about one inch. The wires can be bound tightly into a bundle by wrapping them with a layer of cotton tape that is half lapped and wrapped as tight as possible. The cotton tape is brushed with air-drying insulating varnish, or shellac; and when this is dry, a layer of 0.007-inch empire cloth is placed between two layers of 0.005-inch pressboard, or fish paper, and wrapped around the core. Then one layer of No. 18 double-cotton enameled-covered wire is wound closely and tightly on the core from one end of the wooden end blocks to the other. The ends of the wire leading from the coil should be about 6 inches long and insulated with cotton or varnished cambric sleeving. A layer of empire cloth is wrapped around the coil and the second layer of insulated wire is wound on the core, beginning at the end of the coil where the first layer ended. Another layer of empire cloth is wrapped around the coil and the third layer is wound in place. As soon as a layer of wire is wound on the core, insulating varnish or shellac is applied with a brush so that a solid coil will be formed. The ending end of the top or third layer is connected to the ending end of the first layer and the connection is soldered. The beginning end of the first and second layers are connected to binding 244 REPAIRING ALTERNATING-CURRENT MOTORS 19 posts A and B that are fastened to the board forming the base of the tester. When the insulating varnish on the top layer of the coil has dried, a strip of insulation about one-eighth to one-quarter of an inch in width is removed from the top of the wires for the full length of the coil. The wires in this strip should be polished with sand paper so that they are bright in order that good electrical A B l l l l l l l l 55-VOLT A.C. LINE /// O O O O O O O O O O 0 0 0 0 0 0 0 0 0 0 SECOND LAYER Y-CONNECTED MOTOR WINDING CENTER OF WINDING O l l l l l l l l l l l l l l l l l l l INSIDE LAYER ·14" A l l l l l l l l TOP LAYER NO.22 SOFT IRON WIRE A BINDING POST lllllle MOTOR LEAD lle TELEPHONE RECEIVER 8 "DIA 店 ​WOOD SCREWS B C 55-VOLT A.C. LINE ▲- CONNECTED MOTOR WINDING WOOD BLOCKS -- 4"x4" x 1/4" A A Fig. 10. Details of "Balance Tester" xodo o vr ə eeeeeeeeee 4″--→ el l l l l l l l l e TELEPHONE RECEIVER + B 2014 contact will be made when the tester is used. The center, or middle, turn of the top coil should be located and marked by painting a colored band around the coil at this point. The method of connecting and using the tester is shown at B and C, Fig. 10. The single-phase alternating current is connected to the terminals A and B of the tester. One lead from the winding of the three-phase motor is connected to terminal A and another 245 20 REPAIRING ALTERNATING-CURRENT MOTORS lead of the motor is connected to B, while the third lead is connected to a telephone receiver. The other terminal of the telephone receiver is touched to the bared wires of the outer coil when the switch is closed. If the winding is correctly balanced, there will not be any sound in the telephone receiver when the wire from the receiver is touched to the center point of the upper layer of the winding on the tester coil. If a click is obtained in the receiver, various points to the right and left of the center should be touched with the lead from the receiver until a point is obtained where there is no sound. When the stator winding has been correctly placed and con- nected, the point where no sound is heard in the telephone receiver should not be more than four or five wires from the center point on the coil. If the point is greater than this amount, it indicates (1) that one phase of the winding in the motor has a great number of turns of wire in the winding, which may be due to a mistake in the number of turns of wire in one of the coils or in several; (2) a mis- take in the number of coils connected in each phase; (3) a short- circuited coil; (4) a reversed coil; (5) a reversed pole-phase group; or (6) a reversed phase. While the balance tester is not designed or intended to locate any particular defects, it makes an ideal device for determining if the connections are correct. This device proves very useful in check- ing the connections of the coils and pole-phase groups before they are soldered and for checking the tests made with the compass or growler. It is the usual practice to have another winder check the connections with the diagram before they are soldered and this work requires more time than to make the balance test. This test is often applied after all connections have been soldered and the winding dipped in insulating compound and baked, as it will show quickly if any damage to the windings has occurred while the stator was being handled after being wound. The balance tester with the windings, Fig. 10, is intended to be used for testing induction motor windings designed for 110, 220, or 440 volts. The 55-volt alternating current is obtained from a 110- volt alternating-current line by using a step-down transformer having a ratio of 2 to 1 or by the use of an autotransformer. When the motor winding is for 220 or 440 volts, 110 volts can be used for testing, providing the tests are made very quickly and the current 246 REPAIRING ALTERNATING-CURRENT MOTORS 21 is not kept on for more than a minute. If the current is kept on for much longer, there is danger of overheating the motor winding and damaging it. The balance coil will heat very rapidly, but there is less danger of damaging it than the motor winding because the heat of the coils radiates easily to the air. Wrong Connections. For Voltage. This error can be made by connecting the pole-phase groups of each phase in series instead of parallel or the reverse. For example: The winding on a 440-volt motor may be designed so all the coils and pole-phase groups should be connected in series. By mistake, they are connected so that there are two paths, or circuits, in parallel instead of one. If the motor is connected to a 440-volt line and run without load and the current taken by it is measured with an ammeter, it will be found that the current is nearly as great as the full-load current for that size motor. There will also be a very loud magnetic hum and vibration which shows that the magnetism produced by the current in the windings is much greater than it should be. This is because the voltage forcing the current through the windings is twice that for which they were designed. If a winding is connected so that there are a greater number of coils in series than for which the winding is designed, it is indicated by the current being much less than what it should be for that size motor when it is running idle. When a motor with this connection is being tested by connecting a load to it, it will easily pull out of step and stop when the load is much less than it should be. The stopping of an induction motor due to applying too much load is usually called the "pull out." The point at which this occurs in correctly designed and connected motors is when the motor is de- livering two to three times its full load torque. The majority of wrong connections for voltage is due to getting twice or else only half the correct number of turns or coils in series in each phase. This trouble is usually due to the wrong number of pole-phase groups being connected in series and can be remedied by reconnecting the pole-phase groups. For Speed. This error does not occur very often and is usually found when the motor is given a test run to determine the no-load current taken by the motor. When the motor is running without load, the speed can be determined with a speed counter. When 247 22 REPAIRING ALTERNATING-CURRENT MOTORS making this test, if the alternating current is supplied by a generator in the plant, be certain that the frequency is up to standard. This is very important especially if the current is supplied by a motor- generator set that is operated by a direct-current motor. There is a tendency for the speed of the direct motor to decrease as more load is placed on the motor being tested, and this will decrease the fre- quency of the current produced by the alternating-current generator. This in turn will cause the speed to be much less than that shown on the nameplate. When the current used for testing is supplied by a large power company or central station, it is not necessary to check the frequency, because it is very seldom that it changes or deviates from the standard by more than one cycle per second. The cause of incorrect speed may be due to wrong connections. In this case, the speed will be considerably different from the name- plate speed, especially if the speed is between 900 and 1800 revolu- tions per minute. This is because the motor has been connected for the wrong number of poles. This defect should have been detected when the winding was given the compass test. The remedy is to reconnect the winding for the correct number of poles. A table showing the motor speeds for 25-, 40-, and 60-cycle motors having from 2 to 24 poles is given in the next section. LOCATING MOTOR TROUBLES Hot Bearing. A hot bearing will make itself known in several ways, the most prominent of which are smoking and a high-pitched screeching sound, which is readily recognized by those operating electrical machinery. This is caused by lack of oil, failure of the oil rings to revolve with the shaft, and by dirty or gritty oil. The oil rings should be watched and, in case they do not revolve properly on the shaft, they should be replaced with new ones. A hot bearing is sometimes caused by a shaft being out of true or by a bearing being out of true. This is often caused by too much strain on the pulley. When the shaft is out of true, it is best to re- move the revolving part of the machine, place it in a lathe, straighten the shaft, and smooth and polish the bearing portion of the shaft. It sometimes happens that the hot bearing is due to heat conducted through the iron from the windings. This can usually be noted by comparing the temperature of the bearings and the windings with 248 REPAIRING ALTERNATING-CURRENT MOTORS 23 the hand. When the trouble is due to the windings, the load on the motor, or generator, should be reduced. Hot Windings. This defect is usually first noticed when the insulation on the winding begins to smoke. The machine should be stopped at once and the windings examined. If only a few of the coils are hot, the trouble may be caused by short circuits in that part of the winding, or by one or two grounds. Two grounds in a winding will act the same as short circuit. In case the rotor of the machine is not centered properly and the air gap is less on one side than on the other, there will be a tendency for some of the coils to overheat. If the machine is stopped soon enough, it may not be necessary to replace any coils or only a few of them, instead of re- winding the whole machine. REPAIRING WINDINGS Replacing Defective Coils. When the defects in the windings of single-phase motors or small- and medium-sized polyphase induc- tion motors and generators is confined to one or two coils, it is often possible to remove the defective windings and wind a new coil into the slots without disturbing the other coils. The method of doing the work is very similar to the winding of single-phase motors by hand. With repair jobs, it is often necessary to insert one side of the coil in the bottom of the slot, and in these cases the slot wedges must be removed from the slots containing the defective coils. The top coils that are over the defective bottom coils can be raised partly out of the slot so that new insulation can be placed in the slot. The coil can then be wound in the bottom of the slot by estimating the length of the wire needed and pushing the insulated wire through the slot from the end until the desired number of turns are in place. In winding the wire in the slot, care must be taken to arrange the wires in layers and as tight and as close together as possible other- wise it will be very difficult to place the coil that is in the top of the slot in place. The same kind and size of insulated wire should be used in repair work as was used when the machine was built. The majority of the windings on motors and generators use double cotton-covered copper wire. In repair work, enamel double-cotton covered wire can be used to good advantage because the enamel insulation is very thin 249 24 REPAIRING ALTERNATING-CURRENT MOTORS and does not occupy very much space. The reason that it is not used very much on new work is due to the fact that it is difficult to remove the enamel before soldering the connections. When the wire is of small size, No. 28 or smaller, double-silk covered, or enamel, and a single covering of silk is used. Recording Data. It is desirable that all the necessary data be taken from the old winding before it is removed as it will prevent mistakes and unnecessary time in placing the new winding in posi- tion. If the winding is a new one to the winder, it is best to make a diagram of the connections of the pole-phase groups and the con- nections of the phases. The standard connection diagrams for a certain number of poles and the method of connecting the pole- phase groups in series or in parallel is given in the next section. There are a number of different methods of connecting the pole- phase groups in order to obtain the same number of poles with the series and parallel arrangement of the groups. When the winder has connected a number of motors of the same kind, it is not necessary to draw a diagram; only the necessary data should be taken and recorded, which is as follows: number of coils; number of coil groups; number of coils per group; and coil span, slot 1 to On single-phase machines, the above data should be recorded for both the main and auxiliary or starting windings and, in addition, a sketch should be made showing the connection of these windings. A complete coil should then be removed from the windings for a sample and guide in winding and shaping the new coils. As the winding is being removed, the following data should be taken and recorded: Number of conductors in parallel; number of turns per coil; size of wire; weight of wire; kind of insulation on wire; kind and amount of insulation on coil; kind and amount of insulation in slot, and kind and amount of insulation between phases. The next step is to wind the new coils with the correct size of wire and number of turns as called for in the data taken from the old winding. The method of winding and shaping the coils is the same as described in the preceding sections on direct-current wind- ings and windings on new machines. The detailed procedure will depend entirely upon the equipment available for doing the work. When the coils are to be used in a core that has open slots, it is best 250 REPAIRING ALTERNATING-CURRENT MOTORS 25 Horse- Power 112357 1/2 3/4 11/2 10 15 20 25 30 50 75 712 TABLE I Cost of Rewinding Polyphase Induction Motor Stators Phase-Wound Rotors 1800 R.P.M. or $23 24 28 30 35 40 48 55 65 75 80 90 100 140 190 1200 R.P.M. $25 28 30 35 40 45 55 65 75 85 90 115 125 165 210 900 R.P.M. $32 35 40 43 45 55 65 75 85 95 110 125 145 190 240 to dip the coils in insulating varnish and bake them in an oven the required number of times necessary to obtain a smooth surface. With the majority of generators and motors, however, a partial closed slot is used and for these the coils must not be dipped or baked, because it is necessary to bend the wires when placing them in the slots and the insulation on a dipped coil is too brittle to allow this. When the machine that is to be rewound is of large size or the coils require special size conductors or insulation, it is better to purchase the coils from the manufacturer. The connections of the windings on the armature or stator of a polyphase machine is essen- tially the same for a generator and an induction or synchronous motor. It is not advisable for the average repair shop to attempt to change the number of turns or size of wire in the coils from that of the original machine. However, the coils and pole-phase groups may be reconnected so that the motor can be operated at a changed phase, voltage, frequency, and speed. Cost of Repairs. The prices given in Table I will serve as a guide in estimating the cost of rewinding standard makes of two- or three- phase induction motor stators that can be operated on 110-, 220-, 440-, or 550-volt circuits. The cost of rewinding rotors that have slip-rings and others in which the windings are insulated from the 251 26 REPAIRING ALTERNATING-CURRENT MOTORS core and each other is the same as for stator windings. The above prices assume that the old winding is on the core and a new winding of the same data is placed on the core. When the voltage of the stator winding is 2300, the cost due to the use of a greater amount of insulation will be about 25 per cent higher than for a 110- to 550-volt motor. The connection between the end rings and the copper bars in the slot of a squirrel-cage rotor sometimes become loose or make poor contact. These can be brazed or welded together by using an acetylene torch. The cost of doing this work will be about 20 per cent of the prices given in Table I. There are so many different makes and kinds of single-phase motors that it is impossible to give comparative costs for the different sizes of motors. As a general rule the cost of rewinding a single-phase stator is one and one-half to two times that for a polyphase winding. Reconnecting Windings. It is often necessary to change the connection of the coils and pole-phase groups, number of phases, frequency, and speed from that for which the motor was originally designed in order to enable it to operate at a different voltage. The majority of electrical circuits that furnish power to induction motors are three-phase and have a frequency of 60 cycles. A frequency of 25 cycles is often used in some industrial plants that produce their own power. This frequency is used to a considerable extent in steel rolling mills where it is desirable to operate large machinery at very slow speed. There are some power plants that use a two- phase system having a frequency of 40 cycles per second, although their number is becoming less due to their being changed over to a three-phase system with a frequency of 60 cycles. The great number of changes in the windings are to take care of a change in voltage or speed. Changes in Voltage. It is often necessary to make changes in the windings so that the motor can be operated on a circuit that has a different voltage than that for which it was connected. There is an increasing tendency of the large power companies to furnish power to a customer at 110, 220, or 440 volts for operating motors. When the changes are for voltages similar to these it can be accomplished by changing the pole-phase groupings from parallel to series or the reverse, as in Fig. 11. As an example, assume that the winding has 252 REPAIRING ALTERNATING-CURRENT MOTORS 27 four groups in series as in Fig. 5 and is operated on a 440-volt circuit. The connection of the coils can be represented as a, Fig. 11. It is seen from the diagram that the voltage from each group of coils is 110 volts. For a 220-volt circuit, the coils would be connected as at b, in which there are two groups in series and two series groups in parallel. When it is desired to reconnect it for 110 volts all the coils would be connected in parallel as in c, Fig. 11. ли A- @ b ·440-VOLTS- w --110-VOLTS-|----110-VOLTS- ww ww www m m ww игр www ww K-110-VOLTS--110-VOLTS- -------220-VOLTS-- - - mm fümümüş B mi B 440-VOLTS - Fig. 11. Typical Series and Parallel Connections www. ли m A The windings of a three-phase motor can be changed from delta to star or vice versa and thus enable it to be operated on the new ··254 VOLTS · 110-VOLTS -----110-VOLTS-> A 2 2 Fig. 12. Star and Delta Connections © M 2 W8 mmm ww ww ww K+10-VOLTS-> www. с B me voltage. Thus, if the motor has a star-connected winding, as shown in Fig. 12, and is operated on 440 volts, it can be reconnected for a delta connection that will operate on 254 volts. In Fig. 12 the three phases are represented by the lines marked A, B, and C. The point marked 1, which is the common connection of the three phases, is called the neutral point. The three leads that are brought outside the motor are connected to the terminals marked 2. With a star- 253 28 REPAIRING ALTERNATING-CURRENT MOTORS 3-Ph. Series Star. 3-Ph. 2-Par. Star. 3-Ph. 3-Par. Star. 3-Ph. 4-Par. Star. 3-Ph. 5-Par. Star 3-Ph. Series Delta. 3-Ph. 2-Par. Delta. 3-Ph. 3-Par. Delta. 3-Ph. 4-Par. Delta. 3-Ph. 5-Par. Delta. 2-Ph. Series 2-Ph. 2-Parallel. 2-Ph. 3-Parallel 2-Ph. 4-Parallel. 2-Ph. 5-Parallel. • TABLE II Comparison of Motor Voltages with Various Connections 3-Ph. 3-Ph. 3-Ph. 3-Ph. 3-Ph. 3-Ph. 3-Ph. 3-Ph. 3-Ph. 3-Ph. Series 2-Par. 3-Par. 4-Par. 5-Par. Series 2-Par. 3-Par. 4-Par. 5-Par. 2-Ph. 2-Ph. 2-Ph. Star Star Star Star Star Delta Delta Delta Delta Delta Series 2-Par. 3-Par. 50 33 25 100 200 100 67 50 75 100 300 150 100 400 200 133 500 250 165 173 86 125 58 43 346 172 116 519 86 258 174 129 232 172 290 692 344 865 430 125 63 42 31 63 250 125 84 375 188 125 94 500 250 167 125 313 208 156 625 20 40 60 80 888 58 116 174 232 100 290 35 100 70 200 100 150 105 300 140 215 175 400 200 500 250 25 73 37 50 146 73 75 219 110 100 292 146 125 365 183 19 58 38 87 57 116 76 145 95 50 33 66 100 133 165 24 49 73 97 122 29 42**** 15 29 44 58 73 25 50 75 100 125 18 37 55 73 91 172 23 35 46 58 20 40 60 80 100 15 29 44 58 73 81 162 243 324 405 140 280 420 560 700 100 200 300 400 500 27 54 81 108 135 47 94 141 188 235 41 81 122 163 203 70 140 210 280 350 50 33 100 67 150 100 200 133 250 167 2-Ph. 4-Par. 2-Ph. 5-Par. 20 40 60 80 64 100 35 70 105 84 140 112 175 140 25 20 50 40 75 60 100 80 125 100 ONO PAC 48 28 NOTE-If a motor connected originally as shown in any horizontal column had a normal voltage of 100 its voltage when reconnected as indicated in any vertical column is shown at the intersection of the two columns. 254 REPAIRING ALTERNATING-CURRENT MOTORS 29 or Y-connection the voltage on each phase of the motor winding is about 57.7 per cent of the line voltage. In other words, the voltage between the line wires is 1.73 times that of one of the phase windings. A combination of series-parallel and star-delta methods can be used to good advantage as shown in Table II. It is assumed that the voltage for which the motor was originally connected is 100 volts, while the vertical columns show how the motor was reconnected. The figures at the intersection of the vertical and horizontal columns give the voltage for the reconnection. If it is desired, the numbers can be considered as per cent. It will be seen, that if a 3-phase 4- parallel star-connected motor is reconnected so that it will be a 4- parallel delta-connected motor, it will operate on a voltage that is 58 per cent of its former line voltage. The new voltage can be very easily determined by taking the present connection and following the horizontal line until the vertical line is intersected that has the proper voltage to which it is desired to change the motor. If the voltage given does not vary more than 10 per cent above or below the actual line voltage, the operation of the motor will usually be satisfactory. Changes in Frequency. The most common change in frequency is from 25 cycles to 60 cycles or from 60 to 25 cycles. There is also some changing from 60 cycles to 50 and a few changes from 60 to 40, or the reverse. The most important and easiest noted result of changing the frequency is a change in the speed of the motor. The speed of any alternating motor is expressed in the following formula: Speed (r. p. m.) = number of cycles X120 number of poles 60 Thus, when a 25-cycle motor is operated on a 60-cycle circuit, its speed will be times the speed that it was on 25 cycles. It is usually desirable to keep the speed on the new frequency about the same as the old speed so it will be necessary to change the number of poles in the winding. It is very difficult and frequently impossible to have the same speed at the new frequency. When the frequency is changed from 25 to 60 cycles, the number of poles is usually doubled. A change in frequency also affects the operating voltage in the same direct ratio. Thus, when the frequency is doubled, the new 255 30 REPAIRING ALTERNATING-CURRENT MOTORS voltage must be doubled in order to keep the magnetic and electrical circuits normal. Also, if the frequency is lowered, the voltage will have to be lowered a like amount. Changes in Phase. It is sometimes necessary and desirable to change a motor from 2-phase to 3-phase, or vice versa. In chang- ing, it is usually necessary to reconnect a different number of coils in each pole-phase group. The calculations necessary to determine the number of coils in each pole-phase group should be done by an engineer who is familiar with such calculations. It is not advisable for the electrician to attempt this until he has made a thorough study of the subject. The winding of a single-phase motor is so different from a two- or three-phase motor that it is not advisable to consider such a change. Changes in Speed. A change in speed is made by making a change in the number of poles in the winding. If it is desired to double the speed, the number of poles will be made one-half what it was for the original speed. When the number of poles is changed on a winding, it is usually necessary to make a change in the voltage in the opposite direction in order to keep the magnetic and electrical conditions the same. If the number of poles is doubled, the motor voltage often has to be made one-half what it was formerly. SECTIONAL VIEW OF A PARTLY WOUND TURBO-GENERATOR STATOR CORE; INSET SHOWS CLOSE-UP VIEW OF TEETH AND SLOTS Courtesy of Carnegie-Illinois Steel Corp., Pittsburgh, Pa. 256 CONNECTION DIAGRAMS FOR INDUCTION MOTORS Standard Diagrams. It is impossible to show developed winding diagrams of induction motor connections in the same manner as for direct-current machines, because with the number of poles, phases, slots, and coils per slot the number of diagrams would be several hundred. However, with polyphase induction motors the method of connecting the coils together into groups is the same, and only the method of connecting the groups varies. The method of determining the number of coils in each pole-phase group is described in the section on "Winding Alternating-Current Motors and Generators." This makes it possible to develop stand- ard diagrams that will apply to motors having different coil pitch, number of slots, and number of coils, because the only factors affecting the diagram are the number of phases, number of poles, number of pole-phase groups that are connected in series or in parallel in each phase winding, and on three-phase windings whether the phases are connected in star (Y) or in delta. The number of diagrams needed for a three-phase motor is twice that for a two-phase motor because the phase windings may be connected either in star or delta, while in the two-phase machine or motor the phase windings are not connected together. It some- times happens that a two-phase motor is operated on a two-phase, three-wire system and in these cases one lead of each phase is con- nected to the common line lead for both phases. It is always best to bring the four leads out of a two-phase motor even when it is known that the motor is to be operated on a three-wire system, because the motor may sometime be used on a two-phase, four- wire system and connections can be made without disturbing the windings. Pole-Phase Groups. The pole-phase groups of each phase of a winding can all be connected in series, in parallel, or in a series- parallel combination. The different combinations of coil groupings for motors having from 2 to 24 poles are given in Table I The 257 2 INDUCTION MOTOR DIAGRAMS rated or synchronous speed in revolutions per minute (r.p.m.) is given in this table for 25-, 40-, and 60-cycle motors. Those in heavy type are the standard speeds for motors of 200 horsepower or less, as recommended by the Electric Power Club-an organization including leading manufacturers of electrical machinery. The speed of the motor when operating at full load is sometimes stamped on the nameplate instead of the no-load or synchronous speed. This speed will be less than that given in the table for a motor with that particular number of poles. It will be seen by referring to Table I that with a 6-pole motor there are four methods of connecting the pole-phase groups of coils. The six pole-phase groups can be connected all in series, or three pole-phase groups can be connected in series and these two series groups connected in parallel with each other, or two pole- phase groups of coils can be connected in series and these three series groups connected in parallel with each other, or all six pole-phase groups can be connected in parallel with each other. Explanation of Diagrams. In the standard connection dia- grams each arc or segment of the circle indicates a pole-phase group of coils. In the diagrams in this section, the A-phase groups of coils are represented by heavy lines, the B-phase groups by light lines, and the C-phase groups by heavy dotted lines. In three- phase, star-connected (Y) windings the neutral wire or lead con- necting the ends of the phase windings together is indicated by a medium dot and dash line. A simple diagram in the center shows quickly how the pole-phase groups are connected. The numbers on these coils refer to the pole-phase groups represented by the segments of the circle. The arrows inside the segments of the circle indicate the direction of flow of the current, assuming that it always enters at the external lead and flows to the neutral or to the other phase lead. The arrows are of assistance in checking the con- nections, because for any pole-phase group of any phase they should be pointing in the opposite direction from the preceding group of that phase. The reason for this is that the magnetic polarity produced by the pole-phase groups of coils is north, south, north, etc., on around the stator. Three-Phase 2-Pole Diagrams. The connection diagrams for a three-phase, 2-pole motor are shown in Figs. 1 to 4. In Fig. 1 258 INDUCTION MOTOR DIAGRAMS 3 No. of Poles 2 4 6 8 10 12 14 16 18 20 22 24 No. of COIL GROUPS In Series NOTNOUMNO∞INOONONOTONO#7~00~+~O∞❤❤❤~OREINONI~0*2*** 4 6 3 10 12 6 4 14 16 8 18 9 6 5 22 11 24 12 8 4 3 2 | O 0 In Parallel ONONTONMOONHOOONSTONONTHON∞∞-~~-∞-NTBORONINO~~ 0234 0 0 2 4 0 2 3 6 0 12 2 4 8 0 2 5 10 0 2 3 4 6 12 0 2 7 14 0 2 4 8 16 0 2 3 6 9 18 0 4 5 10 20 0 2 11 22 6 8 *2∞ TABLE I 12 24 SPEED OF MOTOR (r.p.m.) 40-cycle 2400 1200 25-cycle 1500 750 500 375 300 250 214 187 166 150 136 125 800 600 480 400 343 300 266 240 218 200 60-cycle 3600 1800 1200 900 720 600 514 450 400 360 327 300 259 4 INDUCTION MOTOR DIAGRAMS STARTING POINT STARTING POINT A A b Chitam és 4 m m ma 5 ellet 2 m a 4 દ elle 5 hell Fig. 1. 2-Pole, Three-Phase, Series-Star Group Connections 18 6 m TB 2 5 3 m elle 3 ееее Ce s mon | C A. C An a + B Fig. 2. 2-Pole, Three-Phase, Series-Delta Group Connections a a 260 INDUCTION MOTOR DIAGRAMS 5 STARTING POINT STARTING POINT A A A reeeeee eeeeee 4 ເດ 2 eeeeeee eeeeee m र 到 ​↑B 500 5. ele Fig. 3. 2-Pole, Three-Phase, Parallel-Star Group Connections AB 2 ယ်ဒ 00000 r 0000000 3 N 10000 ooooooo 4 ooooooo luj 6 a KC B Fig. 4. 2-Pole, Three-Phase, Parallel-Delta Group Connections 261 6 INDUCTION MOTOR DIAGRAMS the two pole-phase groups of coils of each phase are connected in series and the phases are connected in star, while in Fig. 2 the phases are connected in delta. In the Y connection the a, b, and c ends of the phase windings are connected together, while in the delta connection a is connected to B, b to C, and c to A. The lines marked A, B, and C are the external leads that are brought outside the motor frame. In Figs. 3 and 4 the two pole-phase groups of each phase are connected in parallel. In Fig. 3 the neutral is a ring formed from insulated or rubber-covered wire of a size approximately one-half that of the line leads. The ring construction makes a neat job. It will be seen that the direction of flow of current in any pole- phase group of coils in the four diagrams is the same, and using a different grouping or connection does not change this relation. Three-Phase 4-Pole Diagrams. The different connection diagrams for a three-phase 4-pole motor are shown in Figs. 5 to 10. In Fig. 5 the four pole-phase groups of coils are connected in series and the phases are connected in Y or star while in Fig. 6 the phases are connected in delta. The pole-phase groups are connected in the same manner in both of the diagrams and the only difference is in the way the connections are made beyond the end of the phase windings. In Fig. 6, as in other diagrams of delta con- nections, the leads connecting the end of one phase to the next are represented by dot and dash lines the same as the neutral con- nections. In Figs. 7 and 8 the connections are shown when two pole- phase groups are in series and the two series groups connected in parallel. The neutral connection in Fig. 7 can be made a ring as in Fig. 3 and will be mechanically stronger than that shown. In Fig. 8 a ring is used for each phase and the ends of the two pole- phase groups that are in series are connected to these rings. This method is used when the pole-phase coils are connected in parallel as in Figs. 9 and 10. With the Y connection there are four rings and the pole-phase coils are connected between the phase rings and neutral as in Fig. 9. With the delta connection the pole-phase coils are connected between the phase wires as in Fig. 10. Three-Phase 6-Pole Diagrams. There are four different combinations in which the pole-phase groups of coils can be con- 262 INDUCTION MOTOR DIAGRAMS 7 STARTING POINT A STARTING POINT ❤ M ♥·..... 12 12 C tig 6 ……………… llll ll ll 4 7 10 10 3 llllll BLO DO 10 Fig. 5. 4-Pole, Three-Phase, Series-Star Group Connections робт a 6 3 12 9 mmm $2 811 88 85 TB 4 چ کری lll lll lll ll 4 3 6 9 000 600 4 12 bu»« 8 B B ------- 4-Pole, Three-Phase, Series-Delta Group Connections 263 8 INDUCTION MOTOR DIAGRAMS STARTING POINT Α. STARTING POINT A b • 12 ----- C A • « « « « 40 4 péenê عنهم 10 ele 3 10 10 10 ooo a 8 58 82 ↑B ee 4 Fig. 7. 4-Pole, Three-Phase, Two-Series, Two-Parallel Star Group Connections ogo 4 7 000 12 m 6 m 9 -- 3 A ------- •••• che 8 18 B • 7 ❤ mir de un ------- Fig. 8. 4-Pole, Three-Phase, Two-Series, Two-Parallel Delta Group Connections 264 INDUCTION MOTOR DIAGRAMS 9 STARTING POINT A. STARTING POINT A B By a 12 3 A+ mm - 0000000R Hoooooooo Loooooooo ❤❤. eeeeeeely 5 8 bil 2 10 3 lllllllly ou 00000000 10 000000000 a c 00000000-s 00000000- 00000000-s - 0000000.0 w llllllll Fig. 9. 4-Fole, Three-Phase, Four-Parallel Star Group Connections 4 TB a eeeeeeee llllllll N ~~ 9 a | 11 2 ~ releeeele 4 eeeeeeee Feeeeeeee llllllll 000000000 00000000047 ooooooooo +4 ooooooooo-| CIN BANANA «mine ap man 9 8 A --- ----- Fig. 10. 4-Pole. Three-Phase, Four-Parallel Delta Group Connections 265 10 INDUCTION MOTOR DIAGRAMS nected for a 6-pole winding, as will be seen by referring to Table I, and each combination can be connected either in Y or delta, thus calling for eight diagrams of connections. These diagrams are shown in Figs. 11 to 18. In Figs. 11 and 12 all the pole-phase groups of coils are connected in series, while in Figs. 13 and 14 there are three pole-phase groups in series and two of the series groups are connected in parallel with each other. In these two diagrams the three pole-phase groups on one side of the stator are in series and the three on the other side are in series. This method of con- nection brings the ending or neutral ends of the series pole-phase groups on the opposite side from the starting point or where the external leads are connected to the windings. The external leads are connected to the terminals A, B, and C. In Figs. 15 and 16 there are two pole-phase groups in series and three of these series groups are connected in parallel. In Fig. 15, which is a Y-connected winding, a neutral ring is used; in Fig. 16 three rings are used, and these rings are attached to the external motor leads. When the pole-phase groups are in parallel, as in Figs. 17 and 18, the ring method of connection is used and the pole-phase groups are connected between the phase ring and neutral in Y connection or between two phase rings in the delta connection. Two-Phase 8-Pole Diagrams. The connection diagrams for two-phase, 8-pole windings are shown in Figs. 19 to 22. There are four external leads brought outside the motor from the windings and they are usually marked T1, T2, T3, and T4. The T1 and T3 leads are for one phase and would be connected to A and A' leads in these diagrams, and the T2 and T4 leads would be con- nected to B and B' leads. In these diagrams A and B markings will be used so that they will correspond to the three-phase diagrams. The connecting of the winding for a two-phase motor is simpler than for a three-phase motor, because there are only two phase- groups of coils and when connecting one phase every other group belongs to that phase. One important fact must be remembered: with two-phase windings (and this also applies to single- and three- phase windings) each pole-phase group of that phase must be con- nected so that current will flow in it in the reverse direction from the pole-phase group of that phase on either side of it. This is necessary in order that magnetism produced by the current in that 266 INDUCTION MOTOR DIAGRAMS 11 C .... STARTING POINT C f... A STARTING POINT B Ay M 2 4 de dansanu d DO 4 5 A а RD 600 600 608 602 608 1 4 7 10 13 16 18 5 5 --------- 18 8 16 IVÉNY • Humane 17 11 " 14 7 Fig. 11. 6-Pole, Three-Phase, Series-Star Group Connections 17 17 C 26 178 141 113 08 5&B ச 608 ele ras en vos ene b18 15 12 9 6 3 16 7 byc Homeleg mo ellos elemele eel rele ele voor ele 13 10 7 16 તે mo elemoor ele 8 ·· 15 a 9 8 12 15 pre ell-vosi mee 4 W-40 CM - *** UND GA 15 18 9 14 9 14 ------ 13 A ---- - - - - ΟΙ 13 TRU Fig. 12. 6-Pole, Three-Phase, Series-Delta Group Connections 267 12 INDUCTION MOTOR DIAGRAMS ..... STARTING POINT ne-> STARTING POINT B 3 4 2 « « « « « g 18 + ୮ • • 4 A moele 5 2002 2002 600d 16 13 10 …… For 18 17 -- 17 14. ell 5 17 5 ele 10 7 helllll ele a lllllllll Fig. 13. 6-Pole, Three-Phase, Three-Series, Two-Parallel Star Group Connections 8 16 eee 7 CA 7 hell-llllll ele 13 16 ele 9 6 3 mom m 47 2 a a ell ell lllllllll 12 15 18 15 18 & 8 hellele rele 16 15 -- 15 14 12 14 10 10 3 12 • C Fig. 14. 6-Pole, Three-Phase, Three-Series, Two-Parallel Delta Group Connections 268 INDUCTION MOTOR DIAGRAMS 13 # C •-->- STARTING POINT C ..... A STARTING POINT B ---- ខ. 5 4 18 Fav 16 А годо Froor voor B C с 17 18 4 lllll a 17 6 ટ , 13 roo 10 roo 175 2 THERE ARE THE ONE heeeee mm eee ele O 7 4 mor sobr mor 00000 16 roo 16 Fig. 15. 6-Pole, Three-Phase, Two-Series, Three-Parallel Star Group Connections egelegge f eeeee 6 000 12 voo 7 reelle ∞ UT heee 16 ele 15 eeeee voor 15 8 еееее 15 18 ееее eeeee 3 voooo зовут a 9 roooo 13 10 8 100 3 600 18 медре лебее 15 • END A 9 14 6 က 1 - 9 10 14 13 10 ... 13 Fig. 16. 6-Pole, Three-Phase, Two-Series, Three-Parallel Delta Group Connections 269 14 INDUCTION MOTOR DIAGRAMS B دیا By A b STARTING POINT STARTING POINT א 4 4 Can as an an❤ - 18 18 10 —-—-* heeeeeeee + Feeeeeeee ~ Leeeeeeee 1316 eeeeeeee heeeeeeeee heeeeeeeee a 17 50 Loooooooowc 17 eeeeeeee helleeeee Freeeeeeee heeeeee a Theeeeeeee #heeeeeeee lllllllll 14 17 2 17 14 11 8 5 7 7 roooooooo~ b 16 1000000004= -00000000400 -000000005 ↑ B 16 00000000- a rrrrrrr rooooooo mooooo mm 5 - Fig. 17. 6-Pole, Three-Phase, Six-Parallel Star Group Connections ooooooooo a roooooooo47 -000000000 4 oooooooo I eeeeeeee eeeeeeee • eeeeeeeee •helleeleef. 15 16 00013 500/10 8 Brellllllll یں mooooo ooooooor 15 --- 15 18 14 9 14 10 10 13 13 TRAD G • 12 ------ 12 ❤❤❤………………………………. Fig. 18. 6-Pole, Three-Phase, Six-Parallel Delta Group Connections 270 INDUCTION MOTOR DIAGRAMS 15 phase-group of coils will be of opposite polarity to that produced by the pole-phase groups of that phase on either side of it. In a two-phase winding the direction of the flow of current and magnetic polarity produced by current flowing through the pole-phase groups of coils is different from a three-phase winding, Fig. 19. In this figure the current is entering the winding at the A and B leads and passing out at the A' and B' leads. As indicated by the arrows, the current will flow in the same direction in two adjacent pole-phase groups, then in the opposite direction for two pole-phase groups, then in the first direction for two more groups, and so on, all around the stator winding. When the polarity of the pole-phase groups is checked by passing direct current into the A and B leads and out of the A' and B' leads and testing the polarity of the inside of the stator core with a compass, it will be found that there are two north poles, two south poles, two north poles, etc., together. This is just the opposite of the polarity indications obtained when testing a three-phase winding. If this fact is not remembered there will be confusion when a two-phase winding is being tested, especially when the majority of the work is with three- phase windings. In Fig. 19 all the pole-phase groups of each phase are con- nected in series. In the center of the drawing the simple diagram or representation of a two-phase winding is shown. There is no connection at the center between the two phases. In a two-phase winding the two phases are 90 electrical degrees apart, so in a simple diagram the windings are represented as being at right angles to each other. In Fig. 20 four pole-phase groups are in series and two of these groups are in parallel in each phase. In connecting the pole-phase groups, those in the upper half of the winding beginning at the A lead are connected and then those in the lower half, be- ginning at A, are connected in like manner. This brings the ending end of the windings or connections on the opposite side from the beginning. The external leads that are brought outside of the motor frame can be connected to the A' and B' leads at this point as easily as at any other point. The other two external leads are connected to A and B. A two-series, four-parallel connection is shown in Fig. 21. With this winding the best method of connecting the pole-phase 271 16 INDUCTION MOTOR DIAGRAMS STARTING POINT STARTING POINT A B' A 16 2 16 15 15 A 3 3 7 1 3 5 rellmell ele-eee A 14 3 mon m 14 mon mm 15 13 4 ~ 4 13 4 rele ele 13 ele ele Fig. 19. 8-Pole, Two-Phase, Series Group Connections voor voor eee ele BI B' 5 B'T 16 14 ୯ ell-ele 10 12 eee-eee-eel-ele 2 €8 4 12 9 11 13 15 so soor Noor-woo A' 10 14 5 16 12 6 5 7 moo ooo m 1000 11 9 6 11 11 ΟΙ ∞ 10 9 8 6 Fig. 20. 8-Pole, Two-Phase, Four-Series, Two-Parallel Group Connections A' B' 272 INDUCTION MOTOR DIAGRAMS 17 B' STARTING POINT Α B' A Loo oot 20 A STARTING POINT A' 16 16 15 15 ~/1 A 3 oooooo Ammon mmme 0 0 005 3 14 5 4 14 4 13 1 eeeeee llllllo 000000000 00000000013 roooooooo 5 mw 7A" അ 00-19 rooooooo 11 Booooo ooo 13 ooooooooo15 பை15 13 eeeeee eeeeee 3' Fig. 21. 8-Pole, Two-Phase, Two-Series, Four-Parallel Group Connections ∞ Hellllls eeeeee eeeeee eeeeee B' eeeeeeeee 5 12 5 reeeeeeeee + 12 7 0000 mooooo! A' 11 15 m 600000 6 eeeeeeeee eeeeeeeee-∞ B 6 neeeeeeeee eeeeeeeee eceeeeeee H eeeeeeeee 2 4 6 8 10 12 14 16 'B' 10 7 WE ARE NOT ∞ 10 6 8 6 Fig. 22. 8-Pole, Two-Phase, Eight-Parallel Group Connections 273 18 INDUCTION MOTOR DIAGRAMS groups is to use the ring method, which is similar to that used with parallel connections on three-phase motors. This same method is used on a two-phase winding when all the coils are in parallel, Fig. 22. It is necessary to alter the simple diagram in the center due to the large number of coils in parallel. Three-Phase 8-Pole Diagrams. The connection diagrams for three-phase 8-pole windings are shown in Figs. 23 to 30. In Fig. 23 all the pole-phase groups are connected in series and the phases in Y connection, while in Fig. 24 the phases are connected in delta. The connections when four pole-phase groups are in series and the two series groups in parallel is given in Figs. 25 and 26. The opposite method of connecting the pole-phase groups is shown in Figs. 27 and 28. Here there are two pole-phase groups in series and four of these series groups in parallel. Just as in Figs. 29 and 30, where all the pole-phase groups are connected in parallel, these phase rings are run around the top of the winding and the different pole-phase groups are connected to these rings. Starting Connections. There are several methods used in starting a polyphase, squirrel-cage induction motor. When the size of the motor is five horsepower or less, it is often started by connecting the stator windings directly to the line. On motors of larger size, and sometimes on smaller ones, it is necessary to keep the starting current as low as possible in order not to cause dim- ming of the lights due to a large drop in voltage. In these cases the motors are started by supplying reduced voltage to the windings during the starting period and until the motor has attained nearly full-load speed and then connecting it directly to the line. The reduced voltage can be obtained either by connecting a resistance in series with two of the leads to the stator windings or by using a small autotransformer which is mounted in a metal case with the starting and running switches which connect it to the line and to the stator windings. When the motor attains full speed, the re- sistance or autotransformer is disconnected from the circuit and the stator windings are connected directly to the line. This arrange- ment of apparatus is usually called a compensator or autotrans- former. The autotransformers are usually provided with a number of taps on the windings so that the starting voltage can be varied between 50 to 80 per cent of the line voltage. 274 INDUCTION MOTOR DIAGRAMS 19 C... B --> A STARTING A POINT --------------- ---- 3 STARTING POINT WHAT IS THE 2 1 4 7 10 13 16 19 22 Wrllllreball A m 124 1 8 24 wwwmome 23 5 8 11 8 lbriller 9 23 22 9 238 201 178 14 20 23 lbilly 11: 8 5 B Fig. 23. 8-Pole, Three-Phase, Series-Star Group Connections cmm mm mm m 24 21 18 15 12 9 6 3 10 a : 21 10 چھرو پرو llllll ll llllllll 3 6 9 12 15 18 21 24 a 1/ 22:21 20 m m m mm A 22 19 16 13 10 7 4 1 A || 19 20 - ····· 12 19 18 13 14 18 15 14 16 16 17 ban un u d- ----- 100 4000 4000 • Fig. 24. 8-Pole, Three-Phase, Series-Delta Group Connections 275 20 INDUCTION MOTOR DIAGRAMS C B A STARTING POINT am and STARTING POINT -- 7 VAN • 5+ ---- 8 " 24: m m m 22 19 16 13 5 1 4 7 10 பன்டன்டன் m a ------- 23 8 1910 24 23 J BALAA de manten a • A A A A 148 17 118 820 88 823 58 82 Ο 22 21 lllllllll elenell 20 15 18 21 24 m mon -0 Fig. 25. 8-Pole, Three-Phase, Four-Series, Two-Parallel Star Group Connections sönzőn voor 000 vooroo 16 19 22 so o m or 12 9 6 3 10 relemé elle lllllllll пес 11 22 21 : 20 12 20 19 19 8 Us 13 81 • C ----- 14 115 F ---- 14 16 16 17 day « qan «« « •