Class XHiM Book . fl5 2._ ghtF I'BIS COPYRIGHT DEPOSrr THOMAS A. EDISON Copyright by W. K. L. Dickson THE STANDARD MANUAL OF DYNAMOS AND PRACTICAL APPLICATION OF DYNAMO-ELECTRIC MACHINERY By Carl K. MacFadden Associate Member American Imtitute Electrical Engineers AND Wm. D. Ray Associate Member American Institute Electrical Engineers Vice-President Chicago Electrical Association 19 15 REVISED Yimmm EDITION Laird & Lek, Inc., Publishers CHICAGO Copyright 1915, by Laird & Lee, Inc. Copyright 1906, by William H. Lee. Copyright 1S95, by Laird & Lee. Copyright 1894, by Date & Ruggles. m -8 !9I5 CIA393896 Index. CHAPTER I. — ei.e;me;ntary data . - 7 Units of Electrical Measurement. Ohms Law. CHAPTER II.— MAGNKTISM AND INDUCTION - I5 Methods of Current Generation. CHAPTER III.— THEORY OF DYNAMOS - - 20 Action of Commutators. Methods of Dynamo Control. CHAPTER IV.— CURRENT DISTRIBUTION - - 4I Losses in Copper Conductors. Fuses and Safety Cutouts. CHAPTER V. — TRANSFORMERS - - - - 62 Construction and use. Alternating Current Distribution. CHAPTER VI.— TYPES OF DYNAMOS - - - 76 Direct and Alternating Current. Their Application in Practice. CHAPTER VII,— CAUSES of troubi^e in dynamos 88 Their Remedy and Prevention. Methods of Testing for Faults, etc INDBX CHAPTER VIII.— ARC I.AMPS - - . - loj Direct and Alternating Current. Various Types and Makes. Incandescent Lamps of Various Types, CHAPTER IX. — EI.KCTRIC MOTORS - - - 121 Transmission of Power Dynamos. Direct and Alternating Current. Various Types of Motors. Street Car Systems. Methods of Motor Control. CHAPTER X.— STORAGE BATTERIES - - - 139 Various Types. Their Care. Directions for Charging. CHAPTER XI.— EI.ECTRIC HEATING - - - 154 Electric Cooking. Electric Welding. Electric Metal Working. Station Instruments. Switchboards. HORSE POWER EQUIVALENTS - - - 165 COPPER WIRE DATA 166 Copper Wire Table. Safe Carrying Capacity. Preface. Our aim in bringing out this little book has been to reach a class of readers who, realizing the need of a gen- eral fundamental understanding of the application of Electricity, will read with some benefit, we trust, a few descriptions of the modus operandi of the most generally- used class of Electrical Machinery. It has not been our intention to take up the subjects treated on, in any but the most simple and as we believe, the most easily understood way. It is becoming more necessary each year for the well qualified steam engineer to be somewhat familiar with Dynamo Electric Machinery in order to advance in his calling. A partial understanding at least is now or soon will be almost a necessity for those engaged in nearly all branches of engineering work. There is hardly a pro- fession which electricity in some way has not entered. The vast majority of the men in charge of our practical work have never had the advantage of a technical educa- tion and are therefore unable to follow the advances that are so rapidly being made. The volt, ampere, and ohm and their relations to each other are the first stumbling blocks and the cause is easily seen by inspecting a few books for definitions of these words. We have endeavored to impress as much as possible, the formula expressing Ohms Law, E R on which all calculations necessarily take their start. A 6 PREFACE. thorough understanding of the relations of the volt, ampere and ohm to each other, is without doubt the foundation of all electrical knowledge. We have also endeavored to keep up to the times and believe we give some interesting descriptions of modem electrical apparatus, which will be of value to those whose main source of light on electrical matters come from cat- alogues and newspapers. The dynamo tender, unless partially conversant with the principles on which his machinery operates, will often be perplexed at even the most trivial troubles to which a dynamo is subject. A motorman on our usual electric street cars, could often lessen motor repairs to a great extent by obtaining even an elementary understanding of the motors' action. An understanding of the proper dis- tribution and installation of electric wires would be the means of averting many thousands of dollars loss each year by fire from electrical causes. There are many good books on the various branches of electrical work but they are too often of such a technical nature as to bar the uneducated reader from obtaining much benefit from them. We hope that a close study of the following pages will place the average beginner on such a foundation as to make the other more complete electrical books more easily understood. CarIv K. MacFadden. June I, 1894. Wm. D. Ray. ElyKMENTARY DATA. CHAPTER I. ei.kme:ntary data. What is electricity? A question often asked and prob- ably never as yet clearly answered. Those interested in the practical field, find it almost impossible to keep up to the times, in regard to the laws that govern its generation and control. We know that by means of certain combinations of coils of wire and magnets or by means of chemical action, we can produce, we may say, electricity. We must be content if we master a few leading laws governing the generation and application of the Electric current. Let the Scientists and Philosophers discuss the question as to what electricity is. In dealing with the simple electric current that is generated by dynamos, batteries, etc. , we will find that there are several broad and easily understood laws that govern its practical applications. These laws hold good in all cases and un- der all conditions, and should be thoroughly understood by anyone desiring to learn even the first and most sim- ple effects of a flow of electric current. Probably the easiest way to understand this law will be to take a simple case of a pump connected to a loop of water pipe. The pipe is filled with water and it is evi- dent that if the pump is started there will be a circulation of water from the pump through the pipe and back into 8 KI^KMENTARY DATA. the pump again. The pump furnishes the power to move the water in the pipe — and it is evident that the water moves through the pipe owing to the pressure exerted by the pump on the water. In (figure i) an open tank, (d) is shown into which the water flows from the pipe. The pump takes the water from the tank to keep the pipe filled, and the speed of the water through the FIGURE I. — PUMP FORCING V7ATER THROUGH PIPES. pipe and therefore the quantity of water passing through the pump and pipe in a minute of time, will depend on the pressure given the water by the pump. If we double the pressure of the water and the friction or resistance to the flow of water in the pipe remains constant, the quantity of water handled by the pump will be doubled. In other words by increasing the pres- sure, w^e increase the quantity of water passing through the pipe at exactly the same ratio. Now if we found that a guage placed at (a) would have to register 50 lbs. pressure to make 100 gallons of water pass through the pipe in a minute, it is evident that if the friction in the pipe remained the same, that 100 lbs. pressure ought to put 200 gallons through the pipe. It is also evident that EI/EMKNl'ARY DATA. 9 if icx) feet of pipe a certain size oflFers a definite amount of friction, that twice the length of pipe would have two times the friction or resistance to the flow of water that the loo feet has. Thus to put loo gallons of water a min- ute through a pipe will take yi the pressure required to force 200 gallons through the pipe. This example may serve the purpose of illustrating the principle of the flow of current from a source of electricity. We will let the dynamo take the place of the pump, which will generate the pressure to send the electricity through the circuit which may consist of lamps, etc., connected by means of conducting wires. The friction in the pipe is represen- ted by the ''resistance" of the wire and circuit, and the amount of water used, represent the quantity of the cur- rent of electricity. Instead of using the pound as the unit of water pres- sure we will use the term ' 'volt' ' which is the unit of electrical pressure. We also have a term which denotes the unit of ' 'resistance, which is the equivalent of ' 'fric- tion" used in the illustration ot the pump and pipe. The unit of resistance is called the "ohm." Then lastly the quantity of current in electricity is measured by the unit of current quantity, the "am- pere. ' ' This is the quantity of current that a pressure of one volt will force through a resistance of i ohm. The resistance of a conductor of electricity varies not only with its size or cross section but also with the ma- terial of which it is made. Silver, when pure, is the best conductor of electricity known, but copper, when pure, nearly approaches silver and is so much cheaper that it is used in nearly all cases to distribute current for practical purposes. ro EI^HMKNTARY DATA. The metals in their order for conductivity are as follows: Silver, Copper, Gold, Aluminum, Zinc, Platinum, Iron, Lead, German Silver, Platinum Silver alloy and Mercury. In practice the wires or conductors to carry current are either designated in size by their diameter in thousandths of an inch (or mils) or by the sectional area or cross sec- tion of the wire expressed in circular mils or by the size in number, as measured by the Standard American or Brown & Sharp Wire Guage. A circular mil is a circle ^q^qq inch in diameter. As in the case of pump, the higher the pressure in volts at the dynamo, the larger quantity of electricity (expressed in amperes) will be put through a circuit which has a resistance (expressed in ohms) to the flow of current. Thus if I volt pressure will force i ampere of current through a circuit having i ohm of resistance, it will take 5 volts to force 5 amperes thiough this same i ohm of re- sistance and if this resistance is increased to 2 ohms, the pressure would have to be 10 volts to force 5 amperes of current through it. It will be seen that these terms are dependent on each other and their relation to each other is expressed by what is known as Ohms Law which is expressed: Current Pressure in Volts E in = ^ or C = — Amperes Resistance in Ohms R **C" standing for current, "K" for electro-motive force or volts, and ''R" for resistance expressed in *'Ohms.'* This relation C=B/R must be remembered for it is the fundamental law of the governing of electric currents, and is used as a foundation to obtain all of the more com- EI.KMENTARY DATA. II plex formulas known to the Electrical Engineers. Take the simple case of a certain make of incandescent lamp, the resistance of the lamp in question is found to be 200 ohms The pressure of the circuit on which this lamp is designed to run is 100 volts, and according to Ohms law the current in amperes which 100 volts pres- sure will force through 200 ohms of resistance is ^gg or yi which is the number of amperes such a lamp would allow to pass through it if current at 100 volts pressure was applied. It will thus be seen that it is a very easy matter to ob- tain any one of these quantities, provided we have the other two given, by a simple multiplying or dividing of the two known quantities. The relations to each other are expressed E E C= — , E=R X C, and R= — . R C There is still another term with which the practical man is brought in contact and that is the unit of power, the *'watt." This watt is the /(^ze'^r represented by the passing of i ampere of current through i ohm of resis- tance and can always be obtained of any current by mul- tiplying the number of volts by the number of amperes. Thus in the incandescent lamp before spoken of, the watts used by the lamp would be 100 (volts) x^ (^inp) = 50 (the number of watts), this being the amount of elec- trical energy necessary to be applied continually to keep the lamp burning. Such an incandescent lamp would be termed "a 50 watt incandescent lamp." An arc lamp which needed a current of 10 amperes at a pressure of 50 volts to keep it in operation would be termed a * '500 watt arc lamp". 12 ELEMENTARY DATA. There are two entirely diflferent methods of distribu- ting current to lamps etc., connected to dynamos. The plan illustrated by means of the pump in (figure i) may be seen as applied to a dynamo and lamps in (figure 2) (a), in which the dynamo D supplies current for lamps L, and is known as the Series System. It will be seen in plan (a) that the lamps are connected in "series" that is, the current which passes out from the positive (-|-) D D D d) d) (J) O) 0) (!) Q (!) a) (!) Q ^ ^ ^ ^ ^ ^ ■^ Series (a) Multiple or Parallel (b) Mulliple Series {c) FIGURE 2. — SYSTEMS OF CURRENT DISTRIBUTIOIT. brush of the dynamo must go through the whole series of lamps before the negative ( — ) brush is reached, the number of amperes flowing through the v/ire will be found to be the same at whatever point it is measured, but the pressure in volts will vary with the number of lamps through which current is forced. If each of the lamps required lo amperes of current to bring it up to candle power, and it took 50 volts pressure to put 10 amperes of currei • ^Wough it, or in other words, if the lamp had 5 ELEMENTARY DATA. I3 ohms resistance, then the dynamo would have to generate 50 volts for every lamp in the series of lamps or on a 10 lamp circuit the voltage would be 500, 20 lamps 1000 volts and so on. Such a system of lighting is used in operating the usual type of * 'Series arc lamps." The current in amperes remains nearly constant, but the voltage at the dynamo varies with the number of lamps through which it has to force current. Plan (b), figure 2 shows the Multiple System or the system of placing lamps in parallel or multiple arc. The dynamo (D) furnishes current of a uniform pressure to lamps (L) connected to the mains marked (-[-) and ( — )the current from the dynamo however varies as to its quan- tity in amperes, on the number of paths through the lamps from the positive to the negative mains. This plan of current distribution is used in furnishing current to the usual incandescent lamps, or in any other work requiring a uniform pressure or voltage. It will thus be seen that the multiple system is the opposite from the series system in several ways. In the series system the larger the number of lamps the higher the pressure in volts, although the current in amperes remains constant, while in the multiple system the voltage remains prac- tically uniform and the amperes given out by the dyna- mo varies with the number of lamps connected between the mains. The Multiple-Series plan of distribution is a combina- tion of both the previous methods and is shown in plan (c) figure 2. This system of wiring is used to operate arc lamps on incandescent or constant potential circuits and in the other special places which will be spoken of later on in Chapter IV. 14 KI.EMKNTARY DATA. 746 watts are equal to i electrical horse power and by dividing the output of a dynamo in watts by 746 we can obtain the output of the dynamo in electrical horse- power or E. H. P. 1000 watts = I kilo watt and is a term generally used to give the rating of generators or dynamos. The abbre- viation K. W., is used to express kilo-watt. It is evi- dent that the term kilo- watt as used to describe a dynamo does not denote the voltage, or the current in amperes, which the dynamo may be designed to generate. It sim- ply means, for example, in a i kilo watt generator, that the generator has a capacity of supplying 1000 watts of electricity, which may be represented by i ampere at 1000 volts pressure, 1000 amperes at i volt, 10 amperes at 100 volts, 100 amperes at 10 volts or any other combina- tion of current that equals 1000 watts, as the case may be. A proper description of such a generator would be, for instance, a i kilo watt, 100 volt generator, which of course lets us know that such a dynamo will generate 10 amperes at the 100 volt pressure, thus making one thous- and watts or one kilo-watt. Hence Watts or W. =C x E the product of amperes and volts. The instruments used for measuring electrical pressure in volts are generally called voltmeters, or pressure indi- cators. Those for measuring amperes or quantity are called ammeters. The resistance in ohms is measured usually by means of an instrument called the Wheatstone bridge, or rarely an ohmmeter. Wattmeters are used for measuring watts, or the pro- duct of volts and amperes. MAGNETISM AND INDUCTION. I5 CHAPTER II. MAGNETISM AND INDUCTION. Inasmuch as the generation of dynamo electricity is effected by means of the action of magnetism, it is well to take up the subject of magnets first. A magnet, as known to practice, is a piece of iron or steel, which has the power of attracting other pieces of iron to it. There are two types of magnets, permanent magnets, and electro-magnets. A permanent magnet is usually made of hard tempered steel, which after having been brought under the influence of some magnetizing apparatus, retains a more or less amount of magnetism. We often see them in horse-shoe form, known as horse- shoe magnets. Large permanent magnets, however, are expensive to make, and are extremely weak in compari- son to their weight, and in addition they seldom hold their magnetism for any length of time. The other type, known as the electro-magnet, is quite a diflferent thing. If a piece of iron has wound around it, a few turns of insulated wire, and a current of electricity be passed through the wire, the iron immediately will be magnetized, and will remaij. magnetized as long as the current passes through tW wire. The moment, however, the current through 1 le wire is stopped the iron is no longer magnetized. Tl as l6 MAGNETISM AND INDUCTION. it is seen that the current in passing around the iron has an efifect on it, and magnetizes it. The amount of magnetism shown by the iron centre of the coil will depend on two factors, the number of turns of wire around the core of iron, and the number of amperes of current passing around through the turns. Thus with lo amperes passing around the core, 20 turns of wire will have twice the magnetizing power that 10 turns will have. . The effect will depend on what is known as the number of ' 'ampere turns' ' in the coil of wire, the ampere turns being the product of the number amperes and turns, thus, if we have 10 turns and 10 am- peres passing through them, we have a coil of 100 ampere turns, which will have J4 the effect that 200 am- pere turns will have. It is evident, that 100 turns with one ampere passing through them, will have the same effect as 50 amperes and 2 turns, or 100 amperes and one turn, each of the above quantities being equal to . "X) am- pere turns. We have practically no limit as to the strength of the magnet we may construct. The very powerful magnets used in dynamos lately constructed, are made by winding an immense number of turns on large iron cores, and then sending currents of electricity through them, thus making a large number of ampere turns, and producing an immense magnetic effect. Iron has been spoken of as the cores for the magnets because it is the metal found to be capable of carrying more magnetism than any other. In any coil of wire carrying an electric current we may imagine a large number ''lines of magnetism" being generated by the current, each line starting from the end of the magnet MAGN^ISM AND INDUMION. 17 called the positive end and taking a path through the air or some magnetic material back to the other end of the coil called the negative end. These little loops are thrown out from the end of the coil and will follow the easiest path back to the other end, thus completing a magnetic circuit. A permanent magnet made of hard- ened steel throws out these same little loops from its poles without being excited by means of the passage of a current of electricity arou-nd it. FIGURE 3. — KlvKCTRO-MAGNET AND ARMATURE SHOW- ING WNES OF MAGNETISM. If a piece of iron or steel is placed in such a position with relation to the coil as to be in the magnetic influ- ence or * Afield," a large number of these lines of magnet- ism will take the path through the iron in preference to that through the air owing to the fact that iron will l8 MAGNETISM AND INDUCTION. carry lines of magnetism better than air or any other material. The iron under these conditions will tend to assume the position in which the largest number of the lines of force or magnetism will pass through it, and for this reason iron is * 'attracted" to the coil or mag- net. Some iron carries these lines thousands of times better than air. Figure (3) shows the action on a horse- shoe magnet made of soft iron, having a coil of wire on each limb. The nearer the armature or * 'keeper" of the horse-shoe magnet approaches the ends of the magnet, the stronger will be the pull, owing to the increased number of lines of magnetism it carries. A compass needle points north and south because in that position the metal of the compass is parallel to and is carrying more of the lines of the Earth's magnetism through it, than at any other position. If a coil of wire is wound on a hollow spool of wood or other non-magnetic material, and- a current of electricity be passed through the coil, it will be found that a piece of iron will be drawn up into the coil of wire and tend to assume a central position in the coil. On stopping the flow of current through the coil, the iron core will no longer be attracted. When the core of the coil or *'sel- onoid" as it is called, is in its centre, it is carrying the maximum number of lines of magnetism. The selonoid is a form of magnet often used in the manufacture of arc lamps, etc. , and is adapted for this purpose on account of the large movement of the core compared to that of the armature, or keeper of the usual type of electro-magnet with an iron centre. There is still another wonderful effect of magnetism, that of induction. If a magnet be moved about in the MAGNETISM AND INDUCTION. I^ vicinity of a coil of wire whose ends are connected to a means for measuring the passage of an electric current, it will be found that a current of electricity will be gener- ated in the wire of the coil, and that it flows only when the magnet is being moved near the coil. Also, that as the magnet moves toward the coil» that the current flows in one direction through the coil, and as it is being pulled away, the current flows in an opposite direction. By arranging a suitable set of coils and magnets, in such manner that the coils pass in front of the magnets, we may be able to generate strong currents of electricity, and in fact, all dynamos and generators are operated on this plan. The usual method employed ib to so mount an electro magnet, called the field magnet, that there is a break in the iron magnetic circuit, across which the lines of magnetism will pass in completing their circuit. In this gap in the magnetic circuit, an armature con- sisting of a number of coils of insulated wire mounted on a shaft, is revolved by means of power applied to it. As these coils of insulated wire move through the lines of magnetism, currents of electricity are generated in them which are carried away from the armature, to the lamp, etc., to which the dynamo is connected. 30 THEORY OF DYNAMOS. CHAPTER III. THEORY OF^ DYNAMOS. An electric generator or dynamo is a combination of coils of wire and magnets, which have a movement with relation to each other and which, when supplied with suitable mechanical power will generate currents of electricity. In practice, they consist without exception of an ar- mature in which the currents of electricity are generated, and a field magnet or magnets which furnish the lines of magnetism, through which the coils of wire on the arma- ture pass, and thus generate current. The armature may be, and usually is, the moving part; but this is not by any means a necessary thing, for the field magnets may be made the moving part with the armature stationary and accomplish the same result. At present the stationary armature is found only on a few types of dynamos which are usually used for gener- ating alternating currents. It has been shown that the movement of a coil of wire with its ends connected, in the vicinity or magnetic field of a stationary magnet, will generate currents of electricity in the coil. If the coil of wire approaches the magnet, the flow of current will be in one direction, and if it is drawn away, the current will flow in an opposite direction through the coil. If the coil is held stationary near the mag- THEORY OE DYNAMOS. 21 net, no current will be generated in it. This is all caused by the coil of wire passing through, or * 'cutting'*, the lines of magnetism. The current generated, depends however, on several factors. In the first place let us construct, for illustration, the simplest possible form of a dynamo. To furnish the lines of magnetism, we will use a simple steel horse-shoe shaped permanent magnet, M, see figure 4. I«'IGUR:e 4.— SINGI.K I^OOP ARMATURK WITH COLLECTOR RINGS, REVOLVING BETWEEN POLES OF PERMANENT MAGNET. On a shaft we mount a coil of wire consisting of one convolution, the ends of which are connected to insu- 22 THEORY OF DYNAMOS. lated rings mounted at one end of the shaft and on which two brushes bear, and thus connect the coil of wire to a suitable measuring instrument (a) . In the diagram we will assume that the lines of magnetism are being concentra- ted between the ])oles N end S; N being the north and S the south. Thus if the coil of wire on the armature is revolved on its shaft, it is evident that with the coil in the position shown, will have Its right hand half moving down before the pole S, and the left hand half moving upward before the pole N, and since we assume that there are an immense number of lines of magnetism flowing through the space from N to S, it is evident that the moving coil must *'cuf these lines, and it is this action that generates current, or to be more correct, generates electrical pressure which expends itself in creating a flow of current, the amount depend- ing on the resistance of the circuit. Assuming that the lines of magnetism from the permanent field magnets, remains constant, we will find that the electrical pressure generated, and thus the current will depend on simply the rate at which these lines of magnetism are cut, if at looo revolutions per minute the coil of a single turn will generate 5 volt pressure, 2000 revolutions per min- ute will generate 10 volts pressure. The direction in which the current will flow, will depend on the direction of movement of the conductor through the lines of mag- netism. In a simple loop, whose ends are connected to rings, mounted on shaft as shown in figure 4, the current through half a revolution will flow through the coil in one direction, and in the remaining half revolution the current will flow in an opposite direction. Thus in a THEORY O^ DYNAMOS. 23 complete revolution, the current will flow first in one direction, and then reverse and flow in an opposite direc- tion, and in this way produces what is known as an alter- nating current. This alternating type of current can only be used for certain kinds of work, and to so arrange ths connections that all the impulses or waves of current generated in the armature will be given out in one direc- tion, a commutator is necessary. The action of the com- C- FIGURE 5. — SINGlvE lyOOP ARMATURE ON IRON CORE WITH COMMUTATOR AND BRUSHES. mutator may be understood from study of figure 5, which shows the same loop x>f wire between the poles of a magnet, as v/as shown in figure 4, with the exception that instead of rings mounted in the shaft, with brushes 24 THEORY 01^ DYNAMOS. bearing on them a split ring is shown, each half of whicV is connected to a terminal of the single armature coil of one turn (c). The two half rings are insulated from each other and from the armature shaft, and the action may be described as follows: — From the point (A) figure 5 to the point (B) which is yi revolution, the current flows in such a direction as to make the brush (-]-) a positive brush, that is, the current flows from -|- to — , FIGURE 6. — ALTERNATING CURRENT WAVE. the current generated depending on the rate at which lines of magnetism are being cut by the loop of wire. The current with the loop at the line ( A-B ) will be zero, for this is the point at which the current is revers- ing its direction in the loop, owing to the fact that THEORY Olf DYNAMOS. 25 the direction in which the loop cuts the lines of mag- netism is being changed. From this position on dotted line A — B, the current will gradually rise to a tnaximum when the loop is on the line C — D, which is the point at which a certain given movement of the loop will cut the greatest number of lines of force. The rise and fall oi current in an alternating current circuit may be shown readily by the cut in figure 6. The line A — B repre- senting the zero line or line of no flow of current in the coil. The distance from i to 2 represents one complete revolution and the curved line C represents the current produced by the revolving loop. The portion of the curved line above the zero line represents current flow- ing in a positive direction and the portion below the line will represent the negative flow of current. The total curve from i to 2, represents one complete alternation, which in the combination shown in figure 4, means one revolution. If we had the coil making 2000 revolu- tions per minute, there would be 2000 of such waves as shown in curve i — 2. With a commutator such as shown in figure 5, and with the brushes placed as shown, it will be seen that just as the current in the coil is at zero the commutator has moved in such a position that the brushes are just changing from one segment of the com- mutator to the other, thus keeping the rising side of the loop connected to the negative brush and the down- ward moving side of the loop connected to the positive brush. In this way we can send all the impulses or waves of current from the revolving coil on the circuit in one direction, thus producing a pulsating current, but at the same time one whose flow is always in one direc- tion, The current curve of such a dynamo will now be 26 THEORY O^ DYNAMOS. such as shown in figure 7, in which it will be noticed all of the waves of current are above the zero line A — B. This type of current is known as a direct current of pul- sating character. As before stated the generator, or dy- namo just spoken of, is of the simplest possible form and to make large dynamos for supplying continuous direct current in an economical manner such a primitive dyna- FIGURE 7. — PUI^ATING DIRECT CURRENT WAVE — SINGLE coil. ARJVIATURE. mo as shown, must be greatly improved. In chapter i, we have spoken of electro-magnets as being the only practical form for large and powerful magnets, and we will find that all field magnets for large dynamos are of this type. The armatures of large dynamos, instead of having but a single coil, will often have 100 or more coils, each con- sisting of one or more turns, for if a single turn coil will generate, for instance, i volt, when cutting the magnetic lines at a given rate, a coil of 10 turns of wire in it will generate 10 times the pressure that the i turn will, or 10 volts. And as has been explained, if a piece of iron be placed in a magnetic field, a large number of the lines of THEORY OF DYNAMOS. 27 r^-^ --B FIGURE) 8. •FIvOW OF MAGNETISM THROUGH A RING ARMATURE CORE. FIGURE 9.— FivOW OF MAGNETISM THROUGH A DRUM ARMATURE CORE. ^g THEORY OF DYNAMOS. magnetism will take to the iron in completing their in- dividual circuits, and so it has been found advisable to wind armature coils on an iron core, so that the largest possible number of lines of magnetism flowing from the poles of the field magnets, will flow through the iron ar- mature cores, and in this way, the coils of the armature will cut a larger portion of the lines given out by the field magnets. The reader will easily understand, from the previous description, that the current given out from a single coil armature may be a direct current, but still of a pulsating type, there being in the cases shown, two impulses in each revolution. There are many cases where such a pulsating current wou'd be nearly as objectionable as an alternating cur- rent. To overcome this trouble and to also make a dyna- mo whose efficiency is high enough for practical work, has taken an immense amount of study. To make the principal used to obtain a continuous current, very clear to the reader, it will be well to take up the case of a * 'ring' ' armature on which a single coil is wound. From figure 8 and 9, it will be seen that nearly all the lines of magnetism shown between the pole pieces take the iron path in preference to the air. In the case of the iron ring shown between the pole pieces, N and S, the lines practically divide on the line A — B half taking their path by way of the upper half of the ring, and the remaining half through the lower portion of the ring. Thus with a coil placed as in figure 10, it is evident that practically only the wire on the outer face of the ring will be cutting the lines of magnetism as they pass from the pole pieces to the ring. The coil will generate a THEORY OF DYNAMOS. 29 current while revolving from C to D, the line C— D being the neutral line, or line of commutation, which is the point at which the current will reverse its direction in the moving coil. This is the simplest form of ring armature, a step in advance is the adding of a coil FIGURE 10.— RING ARMATURE OF ONE COII on the opposite side of the ring, and connecting ttirrc in multiple, that is, the current generated by one. coll nas added to it the current of the other coil, whicn adds whatever current it may be generating, to that of the original coil. In this case, the amounts generated in 30 THKORY OF DYNAMOS. two coils will be equal, for when the coil on one side of the ring is generating current, the coil diametrically op- posite must also be generating a like amount, and when connected in multiple as shown the total result at the brushes will be the sum of the two efifects. See figure II. It will be evident also, that while the coils are I^IGURK II. — RING ARMATURE. — TWO :OII.S IN MUI.TIPI.E. moving past the line C-D, fig. 8, they generate no current, since they cut practically no lines of magnetism, and that if two coils were placed on the ring so as to be moving past the line, A — B, they would be generating a maximum amount of current. By connecting these four THEORY OF DYNAMOS. 31 coils as shown in figure 12, we will generate a current having twice as many impulses as in the case of an arma- ture having but one pair of coils in series. The current wave will be represented by figure 13. The line i — 2 representing one revolution. FIGURE 12.— GRAMME RING ARMATURE. FOUR coil. TYPE. This multipljdng of coils can be carried on with econ- omy, until we have some dynamos of this type, having hundreds of coils, and giving practically a perfectly con- tinuous current. The proper placing of the armature coils in the mag- nelic field between the pole pieces of the field magnets. ja THEORY OF DYNAMOS. has taken an immense amount of study and experiment, and we to-day have two general types of armature, the drum and the ring type. The drum armatures are so called from their shape. A cylindrical piece of iron with the armature shaft running through its length from end to end. is covered with coils of wire, which in dynamos FIGURE 13. — CURRENT WAVES OF FOUR COII* RING ARMATURE. having but two field magnet poles, are so wound as to form loops similar to that shown in figure 5. This type of armature, with many coils each of several turns, is the type usually used for incandescent lighting and power work by direct currents. The drum armature is sometimes called Siemens armature, from its inventor. Dynamos having ring armatures have been used to a great extent for arc light work and are certainly a very much easier armature to repair than drum armatures, whose windings usually cross and overlap at the ends of the iron armature cores, and thus increase the liability to make trouble from THEORY OF DYNAMOS. 33 short circuits etc., at these points, which often make it necessary to remove nearly all the armature windings to repair the damaged coil. Ring armatures or Gramme armatures as they are often called, may be repaired quickly by removing the defective coil from the ring, and rewinding with a new coil, or in many cases of FIGURE 14. — OPEN COIL RING ARMATURE. trouble, the damaged coil may be disconnected from the commutator bars, and the two bars to which the coil was connected are then connected by a short piece of wire, and the dynamo will then be able to generate current until repairs are made. 34 THEORY OF DYNAMOS The first arc light dynamos, the Brush and Thompson- Houston makes, have armatures of the ring form, but owing to the peculiar windings on them, cannot be called Gramme armatures. They are known as "open coil'' armatures, while all Gramme ring and drum armatures are known as "closed coil". This distinction is brought about from the fact that drum and ring armatures are, as has been shown, connected between windings or seg- ments, of commutator, in such a way as to leave the armature windings always connected in a permanent way from coil to coil, whereas in open coil armatures as shown in figure 12, it will be seen that the coils are sep- arate and distinct from each other. In both the Brush and Thomson-Houston dynamos, the armature coils are provided with terminals which alter the connections in such a manner as to let the coils in the most active positions give the bulk of the current, and either cut out the less active coils entirely, as in Brush dynamos, or reduce the resistance of such coils to the flow of current by placing them in parallel or multi- ple arc, and then in series with the active coil or coils. The current from both of the dynamos mentioned, is extremely pulsating, compared to current from the usual ring armature, but owing to the well worked out details of construction, insulation, regulation, and to the relia- bility derived therefrom, both Brush and Thomson- Houston arc dynamos are known the world over. Chas. F, Brush, of Cleveland, Ohio, was the pioneer in arc lighting work as the world now knows it, and Profs. Elihu Thomsom and Edw. J, Houston were not far behind him in pioneer work. THEORY O"^ DYNAMOS. 3S FIGURE 15 — SEPARATKlyY EXCITED DYNAMO. We have taken up the fundamental study of armatures and have spoken of electro-magnets for field magnets, and the various methods in vogue for energizing them will now be taken up. It takes a current of electricity, passing around an iron core or center to make an electro magnet, the power of which will vary with the ampere 36 THEORY OF DYNAMOS. turns, or the product of the number of amperes passing and the number of turns of wire around the iron core. The first dynamos built with electro magnets for field magnets were * 'separately excited, ' ' that is, had a separ- ate battery or generator of electricity to furnish current FIGURE 1 6. — SERIES WOUND DYNAMO. to energize them, the plan of connections being shown in figure 15. Then it was seen that the current from the dynamo itself might be used to excite its own field mag- nets and owing to a slight amount of "residual magnet- ism", which always remains in a piece of iron after hav- ing once been magnetized, being present in the field THEORY OT? DYNAMOS. 37 magnets, this was easily accomplished, as shown in figure i6, and is known as a ''series winding" and such a dynamo would be known as a "series wound" dynamo. The field winding carries the whole current of the arma- ture and is connected in series with it. This winding is FIGURE 17.— SHUNT WOUND DYNAMO. generally used in arc light dynamos, and others gener- ating a constant current of high voltage. The plan of a shunt winding is shown in figure 17, and is so called from the fact that the winding forms a "shunt" path around the armature. To make an effici- ent dynamo, the resistance of the shunt winding is made 38 THEORY OF DYNAMOS. quite high, several hundred times the resistance of the armature and as a result, the current through the shunt is small in quantity, but the immense number of turns of small size wire in the coils on the field magnets make the necessary number of ampere turns, and thus the resultant magnetism is the same as that produced in the series dynamo with its large current and small number of turns. Shunt wound dynamos are usually used to generate currents of * 'constant potential" or * 'constant voltage' ' such as is used in operating incandescent lamps, electric motors, etc. Owing to the high cost of wire necessary for shunt windings for dynamos of high volt- age, we will find that practically all shunt dynamos oper- ate at a voltage under 600, in fact, by far the largest number of shunt dynamos operate at a voltage of not over 125 volts. For regulating purposes a rheostat (R) containing resistance wire, is placed in the shunt circuit, and in this way a practically uniform voltage is main- tained at all loads by varying the total resistance of the shunt circuit, and thus the current through it, which must in turn vary the magnetism of the field and in this way raise or lower the voltage, as the case may require. Still another winding is shown in figure 18, known as the* compound winding, and is often used to make a dy- namo self-regulating It is evident, that on a constant potential circuit when additional lamps are turned on, that the dynamo must respond at once and send out a larger number of amperes to take care of the load. Under these conditions, to maintain the voltage constant, we must increase the magnetism of the field magnets to compensate for the increased output. This may be ac- complished in an automatic manner by winding a large THEORY OF DYNAMOS, 39 portion of the field with a shunt winding, which should be of such strength as to generate the rated voltage of the dynamo when there is no load placed on it. Then the series windings must be sufficient to add enough ampere turns as the load rises, to keep the voltage up to standard or in some "over compounded" dynamos to increase the FIGURE l8. — COMPOUND WOUND DYNAMO. voltage slightly as the load increases, so as to compensate for loss in line or feeders supplying lamps, etc. This type of dynamo is largely used in lighting plants having a fluctuating load, and is invariably the type used to gen- erate current for street railway work, where the load is an ever varying quantity, a condition under which the 40 . THEORY OF DYNAMOS. compound wound dynamo is practically the only one which gives satisfaction. There are a number of modifications of these principal windings which are seldom run across and for this reason are not explained in detail; suffice to say, that dynamos can be, and have been made, which, by means of the prin- ciples described, will give a constant current and varying voltage, a constant voltage and a varying current, in both cases the speed being maintained uniform, or as in some cases of dynamos designed to be connected to the axle of a car for train lighting, the voltage remains practically uniform, with a varying current, while the speed alters several hundred per cent. It will be seen that we have various types of armatures and field magnets with their various windings, and it will be be easy to see that it is possible to build dynamos of almost any size, and for any kind or character of current. CURRENT DISTRIBUTION. 4I CHAPTER IV. curre:nt distribution. In the previous chapters, we have treated of direct and alternating current dynamos, and to a certain extent, their application. In this chapter we take up the meth- ods of distributing current to lamps, motors, etc., all of which are deseiving of much study. The dynamo for lighting or power purposes, usually sends current a considerable distance before it is used in the arc or incandescent lamps, motors, etc. It is evident that it is desirable to have as little loss as possible in power, between the dynamo or generator and the point at which the current is used. For this reason, conductors of copper are used, owing to its ^^conductivity," that is, its small resistance to the flow of current. But even in the purest copper, there is some resistance, the amount varying with the length, and also with the diameter or * 'cross-section" of the cop- per. If we attempt to reduce the loss to a very, small amount, the cost of copper will be high and if there is not enough copper, the loss in pressure will be excessive. To prevent a loss of current from the conductors, from them accidentally coming in contact with the ground or other conductors of electricity, the wires are insulated from each other and from all connections to the ground. In high potential work, this insulating of conductors 42 CURRENT DISTRIBUTION. would have to be done for safety to human life, for pres- sure of 600 volts and over are exceedingly dangerous. The distribution of current for series arc lighting is a simple matter, since the current in amperes is constant and uniform in all parts of the circuit and the loss in one portion of the wire circuit will be the same as in any similar length of the same size wire. Thus in calculat- ing losses in the wiring leading to arc lamps in series circuits, the main thing to determine is the total resis- tance of the wire, and, having the resistance in ohms, we easily calculate the number of volts lost in passing the 6, 8 or 10 amperes, as the case may be, through the wire. The loss in volts will be the number of amperes, multi- plied by the number of ohms or, expressed in symbols of ohms law, K=CxR. Thus, on an arc light circuit 10 miles long, consisting of No. 6 B & S Guage Wire, which we may see from con- sulting the wire table in the back of book, has a resis- tance of practically, 2 ohms per mile (2.088) that with 10 amperes of current flowing, that the loss in volts, per mile, will be 10X2 or 20 volts, 10 miles would thus be 200 volts, which is the pressure required to force the cur- rent through ths wire circuit, this being independent of the number of arc lamps in series, each one of which adds from 45 to 50 volts to the 200. Thus a circuit, 10 miles long, of No. 6 wire and 50 — 50 volt lamps connected in series on it, will take a total electro-motive force in volts of 200 (line resistance) -\- 2500, which is the total voltage required for the lamps themselves (50X50) which makes a total of 2700 volts required to force 10 amperes tnrough the circuit with its lamps. The loss in volts bein^ 200, and the total voltage necessary to operate the CURRKNl* DISTRIBUTION. 43 lamps on such a circuit, being 2700, it is evident that the per cent, of loss on such a circuit will be Voo*» or nearly 7X%j which in practice would not be considered exces- sive. If No. 4 B and S wire were used in place of No. 6, 'he loss would have been only 130 volts or 5% loss, but the extra cost of copper wire provided with a good rub- ber insulation, would have been nearly $800 over a No. 6 wire and the extra loss in current is not enough to pay for putting up a No. 4 wire. Smaller wire than No. 6 can hardly be recommended, however, on account of the increased trouble in keeping up a long line of small wire which is likely to be broken easily by sleet, wind, etc. Incandescent lamps are sometimes connected in series in the same manner as arc lamps; but the current will usually be found to be less than 5 amperes, although there are some series incandescent lamps made to run on 10 ampere ci/cuits in series with arc lamps. Owing to the danger co::iriected with the handling of such scries incandescent lamps, due to the high voltage on which they usually operate, they are not in very general use and are being discarded more and more each year for indoor illumination. It will be seen that in any series circuit that if the cir- cuit be broken at any point that it will stop the flow of current through all the lamps connected and for this reason all arc and incandescent lamps designed for series work are provided with **cut out" which preserves the circuit in case of trouble with an individual lamp, so as to allow the remaining lamps to operate. In arc lamps on series circuits, the cut out ''short circuits," the lamp in case of the carbon being consumed or broken or in case of a carbon rod in the lamp, sticking or * 'hanging 44 CURRENT DISTRIBUTION. Up." In the case of incandescent circuits, there is usu- ally provided a socket for the lamp in which is a cut out, designed to preserve the continuity of the circuit in case from a lamp being broken or removed from its socket. Arc lamps for series circuits are nearly always operated on direct current dynamos. However the arc lamp is being adapted to the alternating current more and more and wil probably replace the greater part of direct current arc service. The second and without doubt the most generally used plan of current distribution for either power or illumin- ating purposes, is that by means of the constant poten- tial dynamo and a multiple or multiple series system of distribution. Practically, all incandescent lighting, all distribution of current for power purposes and quite a portion of recent arc lighting plants are furnished with current from constant potential dynamos of either alter- nating and direct types. To distribute current at a constant potential or voltage, great care must be exercised in designing the plan of wiring to be used, for it is a very necessary thing to have the pressure in volts as near a constant quantity as possi- ble. This will be found especially the case in incandes- cent lamp installation. A slight rise of voltage above that for which the lamps are designed, will decrease the life of the lamp to an alarming extent. A slight reduction in the voltage, will increase the life to a great extent but the light given out by the lamp will decrease so much as to be unsatisfactory. The method of calculating the size of wire for constant potential distribution may be easily understood after a study of the relation of size of wire to its resistance. A copper wire 98% pure, which is y^^n o^ an inch or one CURRENT DISTRIBUTION. 45 circular mil. in cross section, will be found to measure 10.355 ohms per foot of length, at a temperature of 20^ Centigrade or 68° Fahrenheit. Knowing the resistance of a wire one mil in diameter and one foot long to be 10.355 ohms, we may then calculate the resistance of any wire, provided we know its length in feet and area in circular mils. On a foot length, a wire 2 circular mils in cross section will have but half the resistance of the wire having one circular mil area or 5.1775 ohms per foot length. The smallest wire usually carried in stock by dealers in wire for magnets, etc., is 25 C. M. in area and is known as a No. 36 wire and has a resistance of .4142 ohms per foot of length or ^ as much as a wire i CM. in area. The smallest wire used in wiring for incandescent lamps and other electric light distribution (No. 16 B. & S.) has an area of 2583 C. M. and a resistance at 68° Fah- renheit of .004009 ohms per foot of length. A No. 6 B. & S. copper wire which has been spoken of as a very largely used size for distribution of arc light current on series circuits, has an area of 26,250 C. M. and a resistance of .0003944 ohms per foot. The temperature of the wire has an effect on the resistance of the metal of which it is made. Copper wire increases its resistance as the tem- perature rises, but for ordinary conditions the rise is so slight that it need not be considered. Knowing the resistance of a certain size wire in ohms per unit length and the distance to lamps or motors from the source of current, we may easily calculate the loss or drop in volts with a given current in amperes passing, by means of the equation, V=CXR, or, the volts lost will equal the num- ber of amperes multiplied by the total resistance, ex- pressed in ohms, of the copper wire. It must be remem- 46 CURRENT DISTRIBUTION. bered that we must look at the loss in the -v/iring as a distinct and separate expenditure of power, which is entirely independent of that taken by lamps, motors, etc to which the wiring conveys current. We have shown how the loss in volts may be calcu- lated, provided w^e know the total resistance of the con- ducting: wires and the current passing through them. The condition most usually encountered is that where the maximum number of volts available to overcome con- ductor resistance is known, and also the distance to the lamps from the source of supply. The unknown quan- tity is the area or size of the wire necessary to carry the amount of current needed at lamps, etc., with the loss in volts decided on. On electric light plants, for example, where i lo volt incandescent lamps are used, we will find that the volt- age, at the dynamo, will probably be from 115 to 125 volts, depending on the distance from the dynamo to the lamps, the difference between 1 10 volts and the voltage found at the dynamos, being the number of volts used to overcome the resistance of the conducting wires. Dyna- mos for supplying direct current for constant potential work are usually shunt or compound wound and by means of a rheostat in series with the field magnet cir- cuit, can have their voltage raised as the load increases, so as to maintain a uniform voltage at the lamps. This energy or power lost, shows itself in heating the copper conductors and of course is a loss which must be made as low as possible without an excessive outlay for copper wire. The loss in watts in a given conductor varies with the square of the number of amperes passing through it Thus, in a conductor having i ohm resistance, 10 volts CURRENT DISTRIBUTION. 47 will pass lo amperes. The loss in watts being the pro- duct of the number of volts and amperes, loXio or loo, which is the number of watts used in such a conductor when lo amperes are passing. If 20 amperes were then passed through the same conductor we w^ould find that it took 20 volts pressure to put it through. The watts used being now 20X20 or 400, or 4 times the power that 10 amperes required. It has been mentioned that this loss shows itself by heating the conductors and in this connection it must be stated that but a slight rise in temperature can be allowed, on account of the danger from fire at points in buildings where the conductors pass near wood etc. If a conductor is enclosed in an insulating covering, its radiating capacity is reduced, for as a general thing, in- sulators are poor conductors of heat. Thus, after a great deal of experimenting under various conditions, a table was made, showing the * 'safe carrying capacity' ' of copper wires of various sizes, (see table in back of book). The carrying capacity given in this table is that allowed by the Board of Underwriters for wires used for interior work. We can see that there are two limits between which we must work. The wires must not be allowed to carry more than their safe carrying capacity, in which case we will probably find that the per cent, of loss would be higher than it should be, nor can we increase the size of our conducting wires to any great extent over that abso- lutely necessary, without making the cost of copper excessive. The fundamental elements of the case now having been explained, let a practical case be taken. I^et the 48 CURRENT DISTRIBUTION, dynamo D, figure 19, designed to furnish a constant potential current, be connected by wires to 100 incandes cent lamps in each of two buildings, 1000 feet distant* The incandescent lamps are to be made to give 16 c. p at JIG volts pressure. The wires from the dynamo to the * 'centre of distribution" will be called ''feeders". The centre of distribution being the point at which the feed- ers are connected to the ' 'mains. ' ^ T feedtt'i iOr«, Vi^'CAt**"- n«!i»"A« FIGURE 19. — PI.AN OF CURRENT DISTRIBUTION SHOWING FEEDERS, MAINS AND PRESSURE WIRES. When the buildings are reached, the wiring then con- sists of "mains" and the service wires, or tap circuits from the mains on which the incandescent lamps are placed. Thus the distributing system of such an incan- CURRENT DISTRIBUTION. 49 descent light plant will consist of feeders, mains and the branch circuits to the lamps to the mains. The aim will be to keep the voltage at the mains, constant and uni- form, the pressure in this case being about 112 volts, and thus allowing for about 2 volts loss at full load, between the mains and the lamps themselves. The dynamo will generate a maximum of 125 volts, thus giving a maxi- mum voltage to be used in overcoming the resistance of the ''feeders" at full load, the difference between 112 and 125 or about 13 volts, which is about 10% of 125 volts. To show the pressure of the mains which we have shown have a voltage but slightly higher than that used by the lamps, "pressure wires" are usually run back from the mains to ''pressure indicators" or voltmeters situated in the dynamo room. Thus at a glance, the dynamo tender can see the exact voltage at the lamps and regulates his dynamo accordingly. Assuming that this is a practical case, we first desire to know what the size of the wire must be for the feeders to carry current for the 200 lamps with a loss of 13 volts or 10% in the wire. The 16 candle power lamps of no volt type, will take practically ^ ampere each. Thus, the dynamos will have to supply 100 amperes for the 200 lamps. The formula for calculating the size of the feeder, is 21.21 C D C. M. = — K C. M.=Area in Circular Mils. 2i.2i=Resistance of 2 feet of copper i mil in diameter. C=Current in amperes. D=Distance in feet, to the lamps. 50 CURRENT DISTRIBUTION. K=Loss in volts in the wire. In the case given, C=ioo, D=iooo and E=I3. Thus the size of the wire in circular mils or C. M. is 2 1. 21X100X1000 =163, 153 13 Thus the wire must have a sectional area of 163,153 cir- cular mils to carry the 100 amperes, 1000 feet, with a loss pressure of 13 volts. By consulting the table of wire in sizes in the back of the book, it will be seen that the nearest size, is No. 000 B. & S., which has an area of 167,800 C. M. The diameter in mils or thousandths of an inch of such a wire is 409.6. Thus it is seen that to maintain a pressure of 112 volts at the buildings 1000 feet from the dynamo, when the 200 lamps are burning, will require a No. 000 B. & S. wire. We have shown the buildings i and 2 to be 200 feet apart, and as before stated, it is desirable to make the loss in the mains as low as possible; in this case for ex- ample, I volt. What size wire must be used ? We will use the formula used in the first case, 21.21 CD C. M. = E there will be a current of 50 amperes in either branch from the centre of distribution to the buildings. Thus in the formula, C=5o amperes, D=ioo feet and B=i foot, thus: 21.21X50X100 ^=C. M. or 106,050 I which is slightly larger than a No. o B. S. wire, which has an area of 105,592 C. M. We now have our CURRENT DISTRIBUTION. 5I wire sizes to deliver current inside the buildings at iii volts, which leaves one volt to be expended in overcom- ing the resistance of the service wires, from the mains to the lamps themselves. This loss is calculated in the same manner as the other two cases. We may in this calculate the size wire necessary to deliver any number amperes any distance at any loss and the formula should be remembered by anyone having any distributing work to do, as it makes him entirely independent of wiring tables, since he has the key to the whole plan himself. In all constant potential distributions, safety devices must be so placed in the conducting wires, as to make it impossible to overload the dynamo or wiring by an extra flow of current, due to metallic contact between the wires, accidentally or otherwise and thus produce what is known as a "short circuit". Short circuits may be caused by two wires having a difference of pressure com- ing in contact with each other or with any other con- ductor, so as to cause an excessive flow of current which may overload the dynamos or perhaps melt the conduct- ing wires unless a safety device is so placed as to cut off" the current until the trouble is remedied. On the usual constant potential circuits used for lighting "fuses", made of an alloy having a low melting point, are placed in the circuit, so as to melt when an excessive amount of current pass through them and thus open the circuit. In figure 19, fuses at A. B. and C. are so placed as to pro- tect the wiring, as shown. The fuses at A. would be of such size, as would carry 100 amperes safely, but any excessive amount above this, would speedily heat the fuses to their melting point and the circuit would then be "open". At B and C the fuses would be 52 CURRENT DISTRIBUTION. of 50 amperes carrying capacity and any rise above 50 amperes would melt the fuse and protect the wiring be- yond it. It should be understood that fuses are used simply to prevent more current to pass through a wire than its safe carrying capacity allows, and whenever placed should be so arranged as to size as to open the circuit before the wire is carrying more than its safe^ carrying capacity. They must melt before the smallest wire which they protect, shall have passing through it more current than the law allows. Fuses even at theii best, are often sluggish in operating, especially when of large size, and great care must alv/ays be exercised in putting the proper fuse in the proper place. For places where an unusually heavy fuse would have to be placed, such as the dynamo room of a street rail- way plant, instead of fuses, "circuit breakers" are often placed, which open the circuit by mechanical means and they are undoubtedly far more reliable and satisfactory than any system fuses could be. The usual plan of oper- ating mechanical circuit breakers, is to have a magnet carrying the whole current of the wire it protects, so arranged as to trip a catch when the maximum current is reached, and this catch releases the contacts, which separate and thus open the circuit. The loss of electrical energy in a conductor of a given resistance varies with the square of the current in am- peres passing through it. If a certain wire has for in- stance, 5 ohms resistance, it will take 10 volts pressure to put 2 amperes through it, the loss in watts being 2X10 or 20. If we pass 4 amperes through this same wire it will take 20 volts, the watts being now 4X20 or 80, thus in doubling the current in a given wire, the loss in watts CURRENT DISTRIBUTION. 53 will be increased 4 times or as before stated, it varies with the square of the current. For the reason that the loss in a conductor varies with the square of the current in amperes passing through it, it has always been the aim of electrical engineers and inventors to make lamps, motors, etc. , operate at as high a voltage as is permissable with due regard to safety and reliability. Up to the present time incandescent lamps um G FIGURE 20.— SIMPIvE MUI.TIPI,E SYSTEM, DYNAMO SUPPI^YING 10 I.AMPS. have not been made so as to give good results at any higher voltage than about 1 10 volts and for this reason we are practically limited to no volts pressure as the highest to be used for the operating of incandescent lamps when placed in multiple. The Edison 3 wire system was designed to make it possible to carry current a much greater distance from the dynamo than was possible by the simple multiple sys- tem without great loss, and by its use the loss can be greatly reduced in a system of distributing current for lighting. The amounts of copper necessary to distribute current for a certain number of lamps, by the 3 wire sys- tem is about ^ of that used in the simple multiple system. The explanation of the plan of wiring will be shown in 54 CURRENT DISTRIBUTION. the figures 20, 21, 22 and 23. In Fig. 20, the no volt dynamo D, is shown connected to its load of 10 incandes- cent lamps. The current flows out from the positive brush and then through the lamps back to the negative FIGURE 21 — TWO DYNAMOS SUPPIyYING 5 I.AMPS EACH, ON MUI.TIPI,E SYSTEM. 6 6000 FIGURE 22. — MUIvTlPLE SERIES SYSTEM FOR lO LAMPS. brush; assuming that each lamp is 32 candle power at no volts pressure, it will take one ampere of current, thus the 10 lamps take 10 amperes of current. This plan CURRENT DISTRIBUTION. 55 as shown in Fig. 20 is a simple multiple plan of wiring Fig. 21 shows the same number of lamps but they are supplied by two dynamos Di, D2, each of half the capacity in amperes but the same voltage as dynamoD in Fig. 20. Thus with the 5 lamps connected to each dynamo, there will be 5 amperes flowing out from the positive brush and through the lamps back to the negative brush of each dynamo. Now, if the two dynamos Di and D2, were connected in series and each of them was designed to generate 1 10 volts it is evident 6UTI Jit^H? FIGURE 23. — EDISON 3 WIRE SYSTEM SUPPI^YING 10 I.AMPS. that the 1 10 volt lamps may be connected in series of two and give their proper candle power as shown in Fig. 22. The current flowing out from the positive brush of Di will be but 5 amperes, for there are now 5 series of 2 lamps each, each series taking i ampere at 220 volts pressure. This plan would not meet practical conditions, for if one lamp of a series of two were turned out, its mate 56 CURRENT DISTRIBUTION. would al^o be extinguished. A single lamp could not be turped on and oflf at will and to make it possible to do so, a tnird wire must be added, Fig. 23, which will make it an icdison 3 wire system. In this case D-|- and D — repre- sent the dynamos Di and D2 in figure 21 & 22. The 3 wires are marked -J-, + and — , and are called respec- tively, positive, neutral and negative wires. The two dynamos are connected in series as in figure 22, and the pressure between the* two outside wires -f- and — , is therefore 220 volts. The pressure of each dynamo being I ID volts, there must be but 1 10 volts pressure between the -{- and the +, or between the + and — wires. The current flowing out from the -\- brush of the dynamo D-|- must be but 5 amperes and as long as the loads in am- peres are equal on both * 'sides' ' of the system there will be no current flowing in or out on the middle or ± wire. If, however, a lamp is turned off" on the ''positive side" of the system, (the lamps supplied by D+) the current flowing out on the + wire will be but 4 amperes, which will destroy the balance and we will then find a current of one ampere flowing out on the neutral wire to make up the 5 amperes needed for the "negative side" of the system. The current flowing on the neutral wire will be the difference between the loads in amperes on the two sides of the 3 wire system. If the loads in amperes on the two sides balance, the station switch on the neutral wire can be opened and the lamps will not be affected. With the neutral switch closed, it is evident that by opening station switch on the positive wire, that all the lamps on the -\- side will be put out, but that the lamps on the — side will burn as usual and if the station switch on the negative wire is opened and the positive and neu- CURRKNT DISTRIBUTION. 57 tral switches closed, the + side will burn and the — side be put out. As to the saving in copper and relative losses in this system as compared to the simple multiple system, it will be noticed that the outside wires carry but half the number of amperes that would be necessary on the mul- tiple system, figure 20, and that the middle or neutral wire usually carries but a small amount as compared to the outside wires. Thus, if for a moment we ignore the necessity for a neutral wire, the size necessary for the 2 outside wires will be found to be but % the size necessary to supply current for the same number of lamps, the same distance from the dynamos, in a simple multiple system of distribution, for the current at 220 volts is but 5 amperes, and the loss is twice as many volts, for if we assume a loss of 2 volts from the dynamo to lamps on the simple multiple system, the dynamo voltage must be 112 volts and the voltage at the lamp is 1 10. Thus in the 3 wire system with each dynamo generating 112 volts, we will have 224 volts between the outside wires at the dyna- mo and since the two 1 10 volt lamps in series need but 220 volts, it will be seen that we can allow a 4 volt loss in our wiring and still have the lamps up to candle power. Thus it will be seen that our loss in volts is 4 instead of 2 and our current in amperes is reduced from 10 to 5, thus, each of our outside wires need but be % the size that would be necessary for the same number of lamps on a simple multiple distribution. As has been stated the middle or neutral wire should carry but a very small amount of current in a well de- signed 3 wire system, but for the reason that the fuses on either of the outside wires might be melted in case of a 58 CURRENT DISTRIBUTION. short circuit and thus make the middle wire carry as much as the outside wire, the rule has been followed, of making the neutral or middle wire as large as either of the inside wires, thus we have 3 wires, each X ^^^ ^^^^ that would have been necessary for each wire of a simple multiple system and the relative amounts of copper will thus be 3XX=^ ^^^ 3 wire or 2X1=2, the size for sim- ple multiple wiring, the relations are thus : ^ to 2 or ^ to I. In calculating wiring for 3 wire distributions we may get the size necessary for a simple multiple system of wiring for the number of lamps we desire to run on the 3 wire system and then divide the area of the wire in cir- cular mils needed for each of the wires of the multiple system by 4, which will give the area of the size wires needed to distribute current to the same number of lamps by means of the 3 wire system. The Bdison 3 wire system is used by nearly all the larger size stations supplying direct current for incan- descent lighting. There are 4 and 5 wire systems sometimes used, which are operated on the same plan as 3 wire systems with the exception that an extra dynamo is used for each addi- tional wire, thus a 5 wire system will have 4 dynamos, or their equivalent, all working on the same lighting sys- tem. It is doubtful if the extra complication necessary with such a system is in the line of economy or not, es- pecially with medium sized plants. . For supplying current to street car motors, a plan of current distribution is used, which in the usual single trolley systems is very different from that used to supply current for illumination. CURREN'C DISTRIBUTION. 59 The usual method employed will be readily understood from figure 24. The dynamo D of the compound wound constant potential t3'pe is designed to generate a varying amount of current at about 500 volts pressure. The pos- itive brush is connected to the trolley line L and the negative brush should be connected to the rail or to the copper wires laid in the ground near the track, which serve as the return circuit for the current. Thus the neg- ative side is always * 'grounded" and in fact, the earth itself is used to a limited extent for the return circuit of the current used in operating the motors on the cars. In most cases it has been found that the earth cannot be *;:S2' Q Q']'St i_A^, ajfi^j, . ,[i^^ =5^ f^erui'y C" l^IGURK 24 — STREET RAII^WAY TROI,I,EY SYSTEM. depended on to furnish a path of low enough resistance to insure satisfactory results and a system of * 'bonding' * is always resorted to. The ''bonding" consists of uniting the ends of the rails together by means of heavy copper "bond wire" thus making use of the metal section of the rail to form a continuous metallic circuit from the cars back to the power house. The question of a good return circuit that is durable, is one that has worried the de- 6o CURRENT DISTRIBUTIQN. signers of electric street railways a great deal. This is owing to electrolytic action on the rails, bond wires or on water and gas pipes or other metal conductors near the line of electric road. If a current of electricity be made to flow from or to a metal plate immersed in a con- ducting fluid, an electro-chemical action is set up which disintegrates or destroys the metal, the rate depending on the amount of current flowing. This same action is taking place on the rgiils and other metal conductors when they are placed in moist earth, and its destructive action will depend on the amount of current flowing from the metal to the earth. In an electric street railway track, if the rail circuit contains considerable resistance, part of the current will flow to the earth from the rail, and if water pipes or other good electrical conductors in the earth are in such a position as to make a part of the return circuit, current will be conducted through them, and the chemical action set upon the metal surfaces will rapidly destroy them and make great trouble. The only way to obviate this trouble is to make the return circuit through the track so good that there will be but little current flowing from the rail to the ground, for the cur- rent will always divide depending on the relative resist- ance of the paths offered it. There are some cases of distribution of street railway current by means of two trolley wires, one of which is connected to the positive brush and the other to the neg- ative. In this case the earth and rails do not form a return circuit, the entire distribution being effected by means of the two trolley wires, between which 500 volts pressure is maintained. The motors are of course con- nected between the two wires, by means of two trolleys, CURRENT DISTRIBUTION. 6l which bear against the trolley wires and thus make con- tact with them. Underground conduit distribution for street railways is gradually being developed, and in some cases we will find the rail being used as a return circuit and in others two underground trolley wires are used, insulated from each other and from the earth, in which case the con- ducting wire of course have no more connection with the rail as a return circuit than the double trolley system of overhead distribution, does with the tracl« circuit. 62 AWERNATING CURRENT. CHAPTER V. TRANSFORMERS AND ALTERNATING CURRENT DISTRIBUTION. In the preceding chapter, we have not spoken of alter- nating current distribution and have purposely avoided doing so for the reason that there are several peculiar characteristics of pulsating and alternating currents which should be thoroughly studied by themselves. By suddenly completing and then breaking an electric circuit, it will be found that there seems to be an action take place, similar to that of inertia. The current does not rise instantly rise to its full value and when the cir- cuit is broken, there will be evidence of the current tend- ing to resist the breaking of the circuit. This effect varies with the * 'inductance' ' of the circuit. The induc- tance being the magnetism producing effect of the circuit. If the circuit is through a coil wound on an iron core, the effect will be much greater than if the wire is not wound in coil form. This action is caused by the lines of magnetism or the magnetic field being generated around the wire when the current is started through it. Each wire has its magnetic influence which is created the instant that the current starts flowing through it. If this wire is part of a coil, its magnetic influence must affect other neighbor- ing wires of the same coil. The effect will always be AI^TKRNATING CURREJNT. 63 Such as to retard the flow of current through such a coil, until the full current strength is reached. The ''self- induction'* as it is called, will vary with the square of the number of turns in the coil. Thus, a coil of 10 turns has 100 times the self induction which a coil of one turn would have. If, then, we connect the terminals of a large coil of wire which surrounds an iron core, to a source of electricity, we will find that it takes an appre- ciable time for the current to reach its full strength, and that when the terminals are disconnected, that a spark will show itself in breaking the contact which is many times larger than it would have been, in case the same amount of current was interrupted, which had not passed through a coil such as described. The self-induction of a circuit, always resists the sudden starting and stopping of a flow of current. This effect may be very easily dem- onstrated by placing an ammeter in series with a field magnet circuit of a shunt wound dynamo and watching the gradual rise in current through the circuit, on con- necting it to a source of electricity. On a ''dead beat" ammeter, that is, an ammeter whose needle comes instantly to the correct reading, without going past it, the gradual rise can be readily seen, and on breaking the field magnet circuit, a flash will take place which clearly shows that the current resists being broken. In fact, the voltage at the terminals of a no volt dynamo field coil circuit, may be several times 1 10 volts the in- stant the circuit is broken and a shock obtained in this janner is often exceedingly painful, if not dangerous. It will now be evident that when a current of electricity is started through a coil of wire, that each wire is send- ing out its magnetic influence, which may effect other 64 AIvXERNATlNG CURRENT. conductors in its vicinity and in fact, if two coils of wire are placed near each other so that the magnetic influence of one coil may affect the other, it will be found that the instant current is started in one coil that a current will at once be generated in the second coil, the amount gen- erated depending on the resistance, etc. , of the second coil. It will be found that the current in the second coil JROn CORE*. J) I000V0LT5. PRiynARV- COIL Of 100 100 VOLTS, SECONDARY. COIL OF 10 FIGURE 25. — IRON CORE WITH PRIMARY AND SECONDARY COII^. will only be generated while the current in the first coil is being increased or diminished and that the instant that the current in the first coil becomes a constant quan- tity that the current in the second coil falls to zero. Also that the current in the second coil flows in one direction during the rise of current in the first coil and that the current flows in an opposite direction when the current in the first coil diminishes in ALTERNATING CURRKlfT. ^S strength. Thus by sending a pulsating or alternating current through the first or primary coil, a pulsating or alternating current may be generated in a second or sec- ondary coily although there is absolutely no metallic connection between them. See figure 25. Alternating current dynamos are easier to build than pulsating direct current dynamos, and are certainly eas- ier to handle. They have no commutator, but instead have collecting rings which are the terminals of the coils on the armature. Brushes bear on these rings and in this manner connect the armature coils to the wiring connected to the lamps, The usual alternating current dynamos used for lighting purposes, give out from 15,000 to 16,000 alternations per minute, although dyna- mos lately constructed are being made from 6,000 to 9,000 alternations per minute, which is in the line of for- eign practice. The usual alternating current dynamo is designed to generate either 1,000 or 2,000 volts and a varying number of amperes, and this pressure is reduced at a transformer y to 50 or 100 volts for use in operating the usual incandescent lamp. The electro-motive force or voltage generated in the secondary coil, as compared to the voltage on the pri- mary, will depend on the relative number of turns in the two coils. If the primary coil is connected to 1000 volts pressure of alternating current and has 100 turns in it, we will have generated in a secondary coil of 10 turns, a pressure of 100 volts, or if there are but 5 turns of wire in the secondary coil, we will have but 50 volts between its ends. We can in this manner generate alternating cur- rents of high voltage and distribute them long distances from the dynamos, with a small loss and when the build- 66 ai,te:rnating current. ing is reached which is to be lighted, the hiejh pressure current is connected to the primary coil of a transformer^ on the secondary coil of which the lamps are connected. If there is i ampere at looo volts or looo watts passed through the primary coil, we will find practically the same number of watts given out by the secondary coils, the only change being that at loo volts we will have a current of lo amperes or at 50 volts — 20 amperes. Thus the current in amperes is increased in proportion to the reduction of pressure and it is possible in this way to generate any voltage desired on the secondary winding, by proportioning the number of turns in the primary and secondary coils. The efficiency of transformers, that is, the proportion of the energy supplied the primary coil given out by the secondary varies in different makes, but at full load, large transformers can be made to give to the secondary from 95% to 97% of the energy supplied the primary. Figure 26, represents an alternating current dynamo, generating a constant pressure of 1000 volts, connected to 2 transformers, i of which (No. i) reduces to 100 volts, the proportion of turns on its primary and secondary coil being 10:1, and the second transformer (No. 2) reduc- ing to 50 volts the proportion of turns in the two coils in this case being 20:1. The same dynamo may supply a third form of trans- former which is called a ' 'step up' ' transformer, the pri- mary coil being supplied with 1000 volts current and the secondary coil supplying a higher voltage, 5000 volts. This is accomplished by winding a proportionately larger number of turns on the secondary coil than is wound on the primary, the proportion being 1:5. ALTERNATING CURRENT. 67 It must be understood that the secondary coil has no metallic connection with the primary coil, and that what- ever current is generated in it, must be due to the induc- tive effect of the current in the primary circuit. To get the maximum effect of the current in the primary cir- cuit on the secondary winding is the first requisite in a good transformer. The coils are therefore both placed on an iron core in such a position that as many as possible of the magnetic too© VOtTS. TRA/^sroi^ ampere at 100 volts are connected to the secondary winding, we will find that the current in the secondary circuit will now be 5 amperes and that the primary current has increased from j^o ampere to f%. If 10 more lamps are now connected to the second- ary, the primary current will be found to be ii^g ampere. In fact, as the current in the secondary winding is in- creased, the primary current is also increased and this increase in the primary should be as many watts as is added to the secondary load. The self-induction and impedance of the primary circuit is being decreased by the mutual inductiofi taking place between the second- ary and primary windings, for as the load increases in the secondary winding, just so much is the counteracting effect of the secondary winding on the primary. Thus owing to the decreased impedance of the primary coil, owing to the effect of the current in the secondary wind- ing more and more current flows through the primary coil, until at full load the primary winding is carrying its maximum current and the secondary is exerting its full contracting effect on the impedance of the primary winding. The efficiency of such a transformer should be about 97% at full load. That is, the secondary wind- ing should be delivering 97% of the energy --applied to the primary coil. Thus it will be seen that alternating current can be distributed at high pressures and then reduced at trans- formers to a voltage suitable for operating incandescent 72 AI.TKRNATING CURRENT. lamps with but a small loss in transformation. The loss in watts in transmitting a certain amount of electricity through a wire of given resistance may be stated as vary- ing with the square of the pressure or voltage at which it is transmitted. Thus to deliver 5000 watts, i mile from the dynamo at 1000 volts pressure, will take jj^ as much copper as that necessary to send the same 5000 watts at 100 volts pres- sure with the same loss. For several reasons, 1000 or at most, 2000 volts pressure is as high as is safe to go in generating current for ordinary lighting plants and most alternating current dynamos are made for either one or the other voltage. In most large alternating current stations the highest volt- age generated is about 6,600 volts which if either stepped up to any voltage from 6,600 to 150,000 volts or stepped down. In many cases it is consumed as it is generated. A transformer may have more than one secondary coil or a single coil may be divided into two or more sections and by varying these connections, it will be possible to get for instance, from the usual form of transformer used in America for incandescent lighting. 50 or 100 volts as desired by connecting the two sections of the secondary in multiple or series with each other. Fuses are usually placed on the primary wires only, in the modern type of transformer. In case of a short circuit in the secondary winding or the wires leading from it, the primary fuse would immediately be melted, and thus open the circuit. When the secondary wires enter buildings the usual method of fusing all circuits must be carried out, not as a protection to the transformer, but as a protection to the smaller tap wires leading to lamps, etc., which unless ai,te;rnating current. 73 provided with fuse wires might in case of a short circuit, melt before the primary transformer fuse would open the circuit. The wiring from the transformers to the lamp should be carefully calculated, owing to the fact that the trans- formers on a constant potential primary circuit cannot provide extra pressure as the load increases so as to com- pensate for loss in the wiring. The wiring on all second- ary circuits should be done so as to provide for a very small drop, for in fact, the secondary voltage gradually falls as the load increases and although in the well de- signed transformers, this drop amounts to but from i % to 2 % , it is oftentimes sufficient, when combined with loss in the secondary circuit, to cause a marked diminuation in candle power of the lamps. Special transformers are often wound so as to give from 30 to 35 volts on the secondary winding, which is the voltage needed to operate the usual type of alternat- ing current arc lamps now on the market. Step up transformers are usually used in places where it is desired to send electricity for lighting, etc., a con- siderable distance from the dynamo. The voltage of the alternating current dynamo or "alternator'* is usually 1000 or 2000 and this is raised in the step up transformers to pressure sometimes as high as 150,000 volts. The current at this pressure is then transmitted in some cases twenty or even one hundred miles and then the pressure is again reduced to that desired for lighting, etc. The usual alternating current dynamo as used for light- ing, supplies a single phase current as distinguished from alternating current dynamos supplying multiphase currents, which may have two^ three or more phases. 74 AI.TERNATING CURRENT. 5rrfGLfr PHAS&. AtTERnATlMO Figure 28— Pi.an A. Uo)X.*\ COfLS 90 Two PHAS6 AtTtllWATlfSfr CtRRtnt Figure 28.— Pi,an B. 3 PH/^SE. ^tjERM/Win^ Ct^V^JW^v^ Figure 28.— Pi,an C AI.TKRNATING CURRENT. 75 A dynamo which supplies an alternating current which consists of a succession of single alternating impulses will be called a single phase dynamo and such a current is a single phase current. If, however, there are two windings or their equivalent on the armature, each of which is sending out a single phase alternating current, the dynamo is now a two-phase d3mamo and by designing the armature coils so that the rise of current in one armature winding is not coincident with the rise in the other winding, peculiar magnetic effects may be produced in a suitable form of magnet by providing it with two windings, which are supplied with current from the two armature windings of the two phase dynamos. Likewise, three windings may be placed on a single armature and thus make a three-phase dynamo generating a three-phase current. The figures 28 show the current wave of a single phase alternating current dynamo (plan a). Plan b, shows a two-phase current, in which the relative amounts of current during a revolu- tion are shown in the two windings. The waves of cur- rent in this case are in quadranture, that is, one coil's current wave is 90° ahead of the current in the other coil. Plan c, shows the relations of the currents in the coils of a three-phase generator. The currents are in this case 120° ahead of each other. 76 TYPES OF DYNAMOS. CHAPTER VI. TYPKS OF DIRECT AND AI.TERNATING CURRENT DYNAMOS. Direct current dynamos are manufactured principally in three types, shunt, series and compound wound. The shunt dynamo is found largely in isolated and central station electric lighting plants, operated on the two and three wire systems, and supplying incandescent lamps, small electric motors and constant potential arc lamps. These three types of machines are made in bipolar (two poles) and multipolar (more than two poles) design as respects field magnets. In the previous chapters, the reader has learned that a current is generated in the armature by the movement of coils of wire in a magnetic field which is usually pro- duced by electric currents flowing through coils encir- cling bodies of iron, called field magnets, and that the electric currents generated in the armature are taken from it by means of the commutator and brushes bearing on it. Consider a U shaped piece of iron forming the field magnet, wound with wire so as to form an electro-mag- net when supplied with the electric current. Now in the shunt dynamo, the two terminal wires of a magnet similar to this are attached to the armature terminals TYPES OF DYNAMOS. 77 and form a shunt around the armature from whence the name * 'shunt dynamo" is derived. By previous application of an electric current to the coils surrounding the iron cores, they have been magnet- ized and iron once magnetized always retains a little of its magnetism, called "residual magnetism". If then, there is the feeble magnetism remaining in the magnet, it follows there must always be a slight magnetic field between the poles of the field magnets and as there is an armature revolving in that field, a current is generated which passes out to the commutator and by brushes is led oflf to the circuit. One path which this current can take is that through these field coils which at once causes them to be more powerfully magnetized and a greater magnetic field is thus produced, hence a greater amount of current is generated in the armature. By this step by step process, the machine slowly "builds up" to the proper potential until the normal magnetization is reached. A rheostat or a variable regulating resistance is in series with and connected in the field circuit which regulates the potential or voltage by varying the current through the fields. When a dynamo is running with no load, all the resistance in the rheostat is generally in circuit. Now as the load increases, whether it be that electric lights are switched on or motors are run, either of these will require dynamo current and the potential of the ar- mature falls slightly. To get more current in the fields so as to raise the potential, we must increase the current through them by manipulating the rheostat. A shunt or compound wound dynamo generally speaking, has its pressure remain constant and the current quantity varies 78 TYPES OF DYNAMOS. as more or less lamps are turned on. The shunt or com- pound wound dynamo for supplying constant potential current usually depends on the varying strength of the field magnets for regulation, but the series wound dyna- mo supplying a constant current is often regulated by * 'armature reaction" alone, the armature reaction being the internal electrical action of the armature windings, which may be used for regulating. The series dynamo is used almost exclusively for series arc lamps, but series motors can be placed on the series dynamo, and operated. The field magnets are in series with the armature and full current of armature must pass through them. Again we find that the series dynamo usually generates a variable pressure and constant cur- rent. Arc lamps are run in series with the dynamo, and if this current supplying them fluctuated, as does that on a shunt machine it would produce great variations in the candle power of the lamps which would make a very un- satisfactory light. The arc lamp when burning on a ten ampere circuit has a resistance between the carbons of 4^ to 5 ohms and to force the requisite lo amperes of current through the arc, a pressure from 45 to 50 volts (CXR=B) is required. If 10 lamps are to be run, the dynamo must supply the 10 amperes at a pressure of 500 volts and the dynamo for this purpose usually has its brushes shifted so as to cut in additional active coils in the armature, which means an increase in pressure or voltage on the line for the extra lamps cut in the circuit. No rheostat is necessary in this case, as the regulation of the armature by the shifting of the brushes keeps the current constant through the fields, the magnetic field of the dynamo always containing the same number of mag- TYPES OF DYNAMOS. 79 netic lines. In the series wound machine the brushes are shifted against the direction of rotation for an increase of load. The compound wound dynamo supplying constant potential current, though embodying the shunt and the series principles, is more a shunt machine than series. Its regulation depends upon its fields. Its voltage is con- stant and ampereage variable. In a well designed dyna- mo after the voltage is regulated by means of the rheo- stat, the machine takes care of itself. The armature rotates in a powerful magnetic field. In either the shunt or compound wound dynamo, it is possible to so propor- tion the field magnets and armature that the * 'non-spark- ing' ' point on the commutator is not shifting as the load varies, although in many makes of dynamos, as the load increases the brushes must be shifted forward in the di- rection of rotation, or sparking will result. This is caused by the magnetic effect of the armature distorting the flow of magnetic lines given out by the field magnets so as to alter the position of the neutral line in the arma- ture. In compound wound dynamos all the current gen- erated in the armature passes through the series windings on the fieldmagnets. The machines are so built that the series winding does the regulating and the magnetic field does not reach its full vStrength until the dynamo is deliver- ing its full current. The dynamo * 'builds up' ' by virtue of its shunt winding and as current is required from the dy- namo for the outside circuits, this same current passes around the series coil of the field magnets, increasing the magnetic field and consequently maintaining the pres- sure uniform. Compound wound dynamos may be com- pounded for any percentage increase in pressure from no 8o TYPES O^ DVNAMOS. load to full load, thus compensating for the **drop" in voltage that occurs on the line when large currents are being passed through them. Alternating current dynanios consist principally of three classes, self excited, separately excited and com- posite or compound. They are almost invariably high voltage machines, from looo volts up and consist in an armature of as many coils in series as there are field magnets and these are much in excess of those on direct current dynamos. A great number of alterations of the current are required for practical work and consequently to keep the armature speed down to a reasonable point, a gieater number of magnet poles are used. Currents generated by the armature are led out in two wires to collector rings, where by brushes connected to the circuit the current is taken to the transformers, etc. The mag- netic field extends from one field magnet to its neighbor on either side of it. The field magnets which are usually wound in opposite directions on each successive pole, are excited in the self excited machine by taking the current of one or more of the armature coils and passing it through a current rectifier. It would be useless to excite the fields by the alternating current as the rapid reversals in the cur- rent unfit it for such service. The alternating current must be commuted to a direct current and the rectifier or two part commutator performs this function, by sending all the impulses through the field magnets in one direction and they are thus excited by a pulsating direct current. The residual magnetism in this case plays a part in the alternating dynamo as it does in the direct. As the ar- mature rotates in the magnetic field, weak alternating currents are generated passing through the rectifier, TYPES OI^ DYNAMOS. 8l thence around the field magnets, again developing great- er currents in the armature until normal magnetism is reached. The separately excited alternator is devoid of a rectifier and has its fields excited by an independent direct current dynamo. Regulation is obtained by vary- ing the current in the field magnets as the load varies by means of a rheostat in the circuit of the direct current dynamo. The composite field or compound alternating dynamo is analogous to the compound direct current dynamo, inasmuch as an additional winding passes around the field magnets in addition to the usual winding found on the separately excited alternating current dynamos. This winding is supplied with a pulsating direct current from a rectifier whicn commutes a portion of the output of armature current, the amount depending on the load in amperes. As the current is increased on the circuit, just so is the current increased in the fields and the potential is gradually increased to overcome the * 'feeder loss.'* A resistance is bridged or shunted across the rectifier which can be varied so as to produce different increases in the pressure at full load to allow for "drop" in line. Other classifications of alternators are made, namely: dynamos in which the field magnets are stationary and armature rotates, dynamos in which the armature is sta- tionary and field magnets rotate and those in which field magnets and armature are stationary and an irregularly shaped iron inductor rotates between the two. The principal of the * 'inductor' ' type of alternating current dynamo is that if the number of lines of magnetism is varied through the stationary armature coil that the same effect will be produced as when the armature coil 82 TYPES OF DYNAMOS. moves so as to cut these lines of magnetism. The revolving iron "inductor" is so shaped that as it revolves it completes and then breaks the magnetic circuit through the armature coil and this of course must genei ate cur- rent in it. Alternating current dynamos are 1 milt for any phase and frequenc}^ but it is not timely to 1 ead the reader further than has been gone into in the pi eceding chapter, as other books cover this advanced woi k. It is frequently the , case that one dynamo is insuffic. ient to supply the circuits that it is feeding at certain hours during the run and it becomes necessary to place an additional dynamo on the circuit. In incandescent light- ing, the machines would be placed in multiple, but in arc lighting they would be connected in series. In the shunt wound dynamo an increase in load means an increase in amperes output with voltage constant, while in the series dynamo an increase in voltage results with the current constant. Therefore, if it is required to run an extra machine on a circuit, if it be a shunt or com- pound of the constant potential type, it is connected in multiple, but if the usual series dynamo, it is put in series. Instances where series dynamos are run in multiple or compound wound dynamos in series are few but explanation will be given their operation. SHUNT WOUND DYNAMOS IN MUI.TIPI.E. The directions to be followed in placing shunt dynamos in multiple is as follows: One dynamo already running — Start second dynamo up to full speed — Set brushes on commutator — Move rhe- ostat handle until voltage of dynamo is the same or slightly greater than that of dynamo already running. TYPES OF DYNAMOS. 83 This can be indicated by a voltmeter. A pilot lamp is usually placed on shunt or compound dynamos and they will roughly indicate when dynamos can be placed in circuit. As soon as switch is thrown connecting both dynamos to the circuit, the load should be equalized on each by cutting in resistance in field circuit on the dyna- mo first running and cutting out resistance on dynamo just switched in. If the voltage of the second dynamo be less than that on the circuit, the dynamo will receive current from the first and operate as a motor turning in the direction of its previous rotation. In taking a ma- chine from the circuit proceed in reverse step. The Kdison three wire systems use shunt and compound dynamos. The two dynamos in this case, the positive dynamo supplying the -f- side and the negative dynamos supplying the — side, are started up as previously explained. Being independent of each other and working on separ- ate circuits, no especial precautions are necessary in starting dynamos. The potential should be kept alike on both machines and when possible, the current in amperes should be the same. If one dynamo carries raore current than another, that difference existi ig, is is carried by the + wire. If, as the load increases, addi- tional dynamos are to be placed in parallel on either side of the system they are placed in, the circuit in the same manner as has been described, one dynamo being in mul- tiple with the + dynamos and the other with the — dynamo. One dynamo may be made to supply a 3 wire system by using a switch that will connect -|- wire with = — wire making the neutral a common return for the two outside wires. This method is not to be recommended 84 O^YPES OF DYNAMOS. unless the original wiring was designed with this object in view. Shunt dynamos may be connected in series when long distance transmission is to be accomplished. The field circuits should be connected so as to form one shunt across the dynamos so run in series and they will thus all be excited equally. All machines in this case should be of the same current capacity and each must be able to carry the maximum current on the circuit, or in the case dynamos of various sizes in series, the current must never rise above the carrying capacity of the smallest armature in curcuit. SERIES DYNAMOS IN SERIES. Dynamos to be thus connected must have same current capacities and the -j- terminal of one must be connected to the — terminal of the other. In a lighting plant, this is readily performed at the switchboard by plug con- nectors. This not so satisfactory as making other com- binations but is often done. If series dynamos are to be connected in multiple, let the armature of one dynamo excite the fields of the other and vice versa, so that if one generates not enough current, it weakens the field of the others and both are equalized. COMPOUND DYNAMOS IN MUI.TIPI,E. The compound dynamo embracing the characteristics of the shunt and series machine, the coupling together becomes an operation including both. In figure 29 two generators are connected for multiple working. One machine is running and the switches Ai for shunt circuit and Bi for series circuit are closed. The armature Di is then generating its normal electro-motive force and cur- TYPES OF DYNAMOS. 85 rents are llowing in the shunt field and the series field circuits. Armature D2 is then run at its normal speed, the switch A2 is thrown, allowing the shunt winding to excite the fields of dynamo D2. The switch C on the equalizer wire is closed and when switch B2 is closed, the machine takes its part ot the load. Before the sec- CONNECTIONS Olf TWO COMPOUND DYNAMOS IN MULTIPLE. end dynamo is coupled in circuit, that is, before switch B2 is closed, the voltage should be about the same as that of the dynamo D i first running. After the two are coupled in circuit, the load on each machine should be balanced by the rheostat. By examining the diagram of circuits, it will be seen that the equalizer wire practically places the two series windings in multiple, and this is necessary, owins^ to the fact, that in case two compound dynamos in multiple were feeding a circuit and were not provided with an equalizing wire, and one dynamo had its voltage slightly decreased from any cause, for instance a slipping belt, that the current in the series coil of the dynamo 86 TYPES OK DYNAMOS. whose voltage was lowered, would necessarily be weak- ened and this of course would still further reduce the voltage of the dynamo in trouble. But in the case of the dynamos provided with an equalizing wire, the two coils being in multiple and of equal resistance, will have the total current output of the two dynamos divide equally between them and thus tend to keep the two dy- namos balanced. The equalizer should have a very low resistance compared, to the series windings so as to per- form its office satisfactory. In cutting out a machine the same steps are taken only in reverse order. Compound dynamos of different current capacities can be run in multiple, if the voltage is the same and the resistance of the series windings are inversely proportional to the cur- rent capacities of the several machines, in other words, if a dynamo produces half as much current as another, its windings should have twice the resistance of the other. The machines also govern each other, as when one ma- chine runs too fast, it does more work and consequently lowers its speed, and momentarily it robs the other machines of part of their load, which makes them run faster and thus producing equality. Compound dynamos may be connected with good results in the manner described under shunt dynamos in series. AWERNATORS IN MUIvTlPI^E. To couple direct current dynamos in multiple we said that their potentials should be alike, but in alternating current dynamos not only this is usually required, but the machines must correspond in phase and frequenc3\ To couple an alternating current dynamo in circuit with another, the impulses in both machines must rise and fall together or be "in step." The frequency, period TYPES OF DYNAMOS. 87 and alternations are directly affected by the speed, for the faster the speed the ^eater the alternations, that is, frequency, and vice-versa. Now when one generator is coupled with another generator or motor and running in step with it, we say they are in synchronism. The instru- ment provided to indicate synchronism is called a synchronizer and is explained in chapter x. To discon- nect alternators when running in parallel, is not as diffi- cult as when coupling in. The main switch of dynamo is opened and then the switch on the exciter circuit to dynamo should be opened. It is a better plan while machines are running on single circuits to reverse this operation, throwing exciter switch first and then machine switch, as there are less chances of injury to alternator. The same efifects which cause alternators to work well in parallel causes them to be opposed and get out of step in series. 88 TROUBI — i— AV-^2RP-^^ZP— ^(^ Gf TV -W—'B^-'W (2>- T^— ^ T>- ■<£>- -©- ■^m -- <2y <2>- N9^ 2 • 4 • 7 • A^e THe PE5T RUNMING POlftTS- FIGURE 35. — SPRAGUK-EDISON STREET CAR MOTOR CONNECTIONS. one, is made with each motor under the car. The resis- tance, Rh., is placed in series with the field coils, a, b and c, which are in series with themselves and with the armature M. The resistance is used in starting the mo- tors, for when the motors are standing still and not pro- ducing any counter B. M. F., they would otherwise allow a large rush of current to take place when they were first started. On the second position this resistance is removed, but 132 TRANSMISSION OI^ POWER. the coils a, b and c, and the armature are still in series relation to each other. The coil a, of the field is now short circuited 3, and in position 4 it is placed in multi- ple with coil b, thus coils b and c in multiple, are now in series with coil c and the armature. Point 5, short cir- cuits the coil c, which is then cut out of circuit entirely on point 6, thus leaving coils a and b in multiple to furnish the magnetism of the fields. In point 7, the three coils a, b and c are placed, in multiple with each other and in series with the armature, and this furnishes the weakest field, and the path of lowest resistance to the flow of cur- rent. The motor on this point is exerting its maximum power. Points 2, 4 and 7 are the best • 'running points'*, and in operating this system, these points should be used in preference to others. In handling the starting switch all movements should be firm and steady. If a point is partially passed, move the handle to the next point, never stop between points. In starting a car, let the car start to move on the first point before moving to the second and thus prevent the heavy rush of current which would take place. The other method of motor control which is in general use, is by means of a variable resistance placed in series with the motor, the fields of which are always in series with the armature and the relations of the coils are not varied except after all the resistance has been cut out of circuit, when the field strength is sometimes weakened by cutting out or short circuiting a section of the field coil, which must of course raise the speed to the maxi- mum. Except at the point at which all resistance is cut out, the efficiency of this method is not usuallyas high as in the commutated field method of regulation, but the TRANSMISSION OF POWER. I33 simplicity of the plan is such as to largely overcome this objection, and this plan is used by Thomson-Houston Co. on most of their equipments. The Westinghouse Co. use practically the same methods of motor control on their usual street railway apparatus. There has lately been revived a method of series multi- ple connection of motors, which is now being adopted by roads on account of its economy. The motors are two in number, as usual in American street car practice, and they are adapted to be connected in series on starting the motors, which placed 250 volts on each motor. With this manner of connections, the motors will operate very economically at low speeds, such as would be used in going through crowded streets of large cities. When a higher speed is required, the motors are placed in multi- ple on the 500 volt lines and the motors at once run at a much increased speed. In this method of motor control, the fields are sometimes divided in sections, or as in the usual type of Westinghouse Series multiple controller, the entire changes are affected by varying the connec- tions of the motors and a resistance placed in series with them. A later method of motor regulation as used by the General Electric Co., consists of a resistance adapted to be placed in shunt or parallel with the series field coils, when maximum speed is desired. This shunt resistance of course robs the fields of part of their current, and weakens them and thus increases the armature speed. The plan of series multiple connections of the General Electric Co., is shown in figure 36, in which i and 2 rep- resent the two motors under the car. The connections as made by the movement of the con- i34 TRANSMISSION OF POWER. troUer switch, are shown starting with the *'off" point, and ending with the two motors in multiple on full line pressure with the field windings shunted by means of the resistance Ri and R2, and thus running at their highest speed. In starting on first point, the resistance Rhi and Rb2, is placed in series with the motors which are in series relation to each other. ^£R1E.^ -nt)lTrPL£ ' CONNECTIONS r T v-4— A/VA/V— -^m^ — V\/ (^—ws^ — et- t^^ <£>-w^r — 0' t^ poiKTS 5 • 7 • ARE ^.9'f fttjsMiMa P01M6 — & e^-^WT^ Ia/VW\AIb,4' ff- FIGURE 36 — SERIES MUI,TIPI.E STREET CAR MOTOR CONNECTIONS. On the second point, }i of the resistance Rhi and RI12I is cut out and on the third point, all the resistance in series with the motors is removed, and on the fourth point the field coils are shunted by the resistance Ri and R2. The points 5, 6 and 7, are not running points and are not marked on top of the controller box or stand. During these points, the motors are being changed from series to TRANSMISSION OF POWER. I35 parallel relation, as shown in point 8, and from this to the maximum speed point at number 10. Motors are known in types, as ^^gearless", * 'single reduction" and ^'double reduction", owing to the various methods of connecting the revolving armature to the car axles. A gearless motor is mounted on the axle usually, except in one case where a single large motor is con- nected to the two car wheels by means of connecting rods, such as are used on locomotives. The gearless and single reduction type of motor has been brought out within the last year or so and to-day the majority of roads use the double reduction motors, which although noisy and necessitating large repairs on the double set of gear- ing, are usually of light weight for the power developed and are, if anything, more efficient than the heavier slower speed motors. The single reduction motors of various makes do away to a large extent with the gearing repairs and seem to be the most desirable for the usual street car service. These motors are not excessively heavy and are as a gen- eral rule more efficient than the gearless types. For high speed service, the problem is somewhat dif- ferent and the gearless motors should be well adapted to this service, for the armature speed would be high and the motor quite efficient. Owing to a lack of room under a car for motors, gearless motors are difficult to build of sufficient power and efficiency that will go in the limited space allowed. It should be remembered in this connection, that the high speed motor is a much lighter motor for a given power than a slower speed motor. Thus as the armature speed is reduced, the magnetic field must be increased in 136 TRANSMISSION OF POWKR. strength or the armature coils must be increased in size and number, which means a heavier motor. Street car motor repairs are often heavy and expensive and in many cases are due to careless handling. The usual street car motor of any make or type is always working under disadvantages compared to stationary motors protected from the weather. The street car motor is exposed to dust and dirt in dry weather, and water and mud in wet weather, and owing to the high pressure used, 500 volts, it is often most diflBicult to keep armature and fields from grounding and thus disabling them. The frames of the motors are of course connected to the metal car trucks, which are grounded, and in wet weather water or mud may ground or short circuit the fields or armature of the motors. "Bucking" is the usual name given to a violent jerk which often takes place when a motor is grounded. Its act- ion is very much like that of a "bucking bronco" and may strip the cogs from the gears or shake up the passengers badly, depending on its severity. If a motor is running at full speed and a ground occurs on the wire between the fields and the armature of the motor, the fields are often made to carry a much greater amount of current than they should. The armature at once begins to act as a generator and ' 'bucks' ' . A flash from brush to brush across the commutator will often cause the same effect. In case of trouble of this kind, look for a grounded field or brush terminal. If the motor is permanently ground- ed, cut it out and proceed to the barns with one motor. The brushes and commutator of a motor should receive excellent care. In case of sparking-, see that your brushes axe being pressed against the commutator firmly by the TRANSMISSION OF POWER. 137 springiL and that they are properly fitted to the commuta- tor surface. Copper coated carbon brushes are superior to those not coppered, for they heat less. Never reverse a car when running if it can be possibly avoided, and then it should be done in a moderate man- ner or the fuse is likely to ''blow" or the cogs to break, and thus effectually stop all chances of stopping suddenly in this way. In going down grades it is bad policy to run at an excessive speed, experience having shown that several of the worst accidents which have ever occurred on electric railways, were caused by run-away cars on grades. The series multiple controller or start- ing switches are provided in some cases with a locking switch, which prevents a motor being reversed while cur- rent is on the motors. In climbing grades, always run on one of the ''best running points", and thus avoid any possible damage from overheating field and armature coils. On a slippery rail, care must be used in starting, to avoid slipping. A moderate use of sand is recommen- ded and in case wheels slip as speed increases, move starting handle back and throw on current again gradu- ally. Go slowly around curves, for your trolley is not only likely to jump off the wire, but broken and dam- aged trucks are often the result of such reckless running. The trolley pole is also likely to break span wires, etc. , of the trolley line. A motorman should never leave the car without first removing the starting handle from starting box. Motor cars, if properly designed, should be able to mount grades of 15% to 18% and several roads in Amer- ica are operating daily on grades of 13% and over. Incandescent lamps in street cars are usually connected 138 TRANSMISSION OF POWER. SO as to place five 100 volt lamps in series. Some cars have one set and others two, and as a general rule electric cars are the best lighted of any cars used for passenger trans- portation in the country. Incandescent lamps, when placed in series, should always be of '.he same make and candle power, to give the best results. Lamps should not be allow^ed to become loose in their sockets, for socket repairs are sure to follow. STORAGE BATTERIES. I39 CHAPTER X. STORAGE BATTERIES. Electricity passing through a liquid solution from one metal plate to another will produce chemical action. The action will depend on the quantity of current used, the kind of solution and the material of which the plates are made. The history of the storage battery or * electrical accu- mulator" dates back to 1 801, when one of the scientists of the day noticed that if two plates of the same metal were immersed in an acid solution and current be passed from one plate to the other, that after they had been dis- connected, electric currents could be obtained from the plates by connecting them together by a conductor, the current flowing in an opposite direction to that o\ the current with which the **cell" had been charged. No material progress seems to have been made from this date until 1859, when Planted, while experimenting in this line, made a storage battery consisting of sheets of lead immersed in a solution of dilute sulphuric acid. He found that w^hen currents of electricity were passed though the solution from one plate to the other, that a chemical action was at once set up, tending to change the chemical composition of the lead plates, one of which being connected to the positive pole of a primary battery would gradually assume a reddish color and the other I40 STORAGE BATTERIES. remaining practically unchanged. He found that after current had been sent through the battery, that it would exert a counter Electro Motive Force, (counter K. M. F.) of from 2 to 2.5 volts and that in discharging the cell, that it would show an B. M. F. of about two volts until there had been given back from the cell nearly the amount of current used iu charging it. He also found that by charging a cell and then discharging it, and then revers- ing the cell and charging it in the opposite direction that its storage capacity would be increased to a large extent, and this process of **forming" the plates w^as always gone through until the plates became porous and would hold a charge of many times what they would at first. This forming was necessarily a long, tedious and expensive operation, and some time later it was discovered by Faure, that if a paste made of oxide of lead be supplied to a lead supporting plate, called a * 'grid' ' that the pro- cess of forming was so shortened as to be practically done away with. It also made it possible to reduce the weight of the plates to a great extent and the majority of electrical accumulators or storage batteries used m Amer- ica are now made on this plan. It will be evident that it will be necessary in any bat- tery to provide means for keeping the positive and neg- ative plates from touching each other, and thus short circuiting. Various methods have been tried, a few of which will be mentioned. Hard rubber * 'combs'* or **hair pins" may be placed on the plates and thus keep them separated from each other. In one type of battery using pasted plates and "grids'' for supporting the active material, plugs of active material in the negative plates are removed in certain places in the plate and rubber STORAGE BATTe:RIES. 14 X FIGURE 37. — STORAGE BATTERY PIRATES. PASTED PLATE TYPE. plugs are placed in these openings so as to hold the posi- tive plates away. In other cases a perforated hard rub- ber plate or a sheet of asbestos paper is placed between the plates. Owing to the * 'buckling" of the lead plates, it is often a very difficult matter to keep the plates apart, 142 STORAGE BATTERIES. and in case of contact, the cell will at once become dis- charged and very likely injured. A deposit of active material often forms at the bottom of the retaining cell and unless the plates are raised some distance from the bottom of the cell, trouble may arise from a short circuit at this point. It should be understood that no matter how large a single storage cell, either of the Plante'' or Faure type may be, or how many plates it may contain, that its volt- age will never be higher than from 2 to 2.5 volts. The * 'ampere hour" capacity will vary however, with the size and number of plates exposed to the solution, and to get a voltage of say, 100 volts, it will always be necessary to connect at least 50 coils of battery in series, each cell having about two volts B. M. F. There is always a max- imum charging rate for a given size plate, which should never be exceeded. A plate when being supplied with more than this rate will be likely to be injured by warp- ing or by being "buckled" as this bending or warping of the plates in called. The cells are rated on their ' 'ampere hour capacity" and each size of cell with its ''elements" will have a rate at which it may be charged and dis- charged giving its maximum elB&ciency. A well known make of storage battery of 150 ampere hour capacity, may be described as as follows: — voltage about two volts — number of plates 23, 11 of which are positive and 12 negative, thus giving each of the positive plates a neg- ative plate either side of it. The size of both positive and negative plates are the same, i2X6X}i inches thick. The normal charging rate is about 25 amperes and the discharge rate from 25 to 30 amperes. The weight of cell and liquid complete is about 45 pounds. STORAGE BATTERIES. 1 43 The discharge rate may be slightly increased, but the capacity of the cell will be diminished to a considerable extent. We have stated that the large number of American made storage batteries are manufactured on the * 'pasted plate" or Faure principle, but of late many cells of the Plants' type are being used in America. The mechanical construction however, of the plates is very different from the original Plante^ battery. In one leading make of the Plante^ type of battery, the plates are formed of lead ribbon whose surface has been previously roughened, the ribbons being about ^ to ^ inches wide and placed in a horizontal position between heavy lead end supports. The plate really consists of a large number of thin lead strips, piled one over another until the plate when complete measures in the medium sizes about 6xSX/4 inches thick. A number of such plates are then connected by means of lead lugs on the heavy frame of the plates, and in this way a completed cell is put together, and the plates are now ready for * 'forming". This is done in the usual manner, the per- Dxide of lead formed from the ribbons fills up the spaces between them and at last forms a practically solid plate of **active material" as the peroxide of lead is called. There is always supposed to be enough of the lead ribbon left to form a support for the active material and when such batteries are properly cared for, they should give good results. They will stand a heavy discharge with- out buckling and will withstand considerable hard usage such as is experienced in train lighting, etc. The positive and negative plates of lead batteries, may be easily distinguished by their color, the positive plates 144 STORAGE BATTERIES. being of a reddish color and the "negatives" of a metallic lead color. When in good condition and fully charged, the * 'positives" should be of a dark plum color. The solution of sulphuric acid and water in the plates are immersed will be found to vary in its specific gravity with the charge in the cell. When the cells are com- pletely discharged, its specific gravity should be from 1. 15 to 1. 16 and when fully charged, its specific gravity will be somewhat greater. The mixture is about ^q acid and 1% water and* should be tested after mixing with a hydrometer, which gives the specific gravity. The solu- tion evaporates rapidly when in a cell which is in actual service and w^ater should be added to keep the solution right. If the solution does not contain enough acid, pour in solution already mixed and never pour clear acid in on the plates to increase the specific gravity of the solution. In charging storage batteries, the positive terminal of the dynamo should be connected to the positive terminal of the series of cells. In charging the usual lead storage battery, it will be found that until the batteries are almost charged, the electro motive force of each cell will be from 2 to 2. i volts, but as the charging progresses, the voltage may rise as high as 2.3 volts, but when the charging current is stopped, the voltage falls to about two volts. A low reading voltmeter should be used in testing storage bat- teries and the terminal reading of a single cell is usually a correct showing of the condition of the cell. If it is found that a single cell tests lower than the others in series with it, the cell should be removed and exam- ined. It may be found that the plates are buckled and in this case they must be straightened again by mechani- cal means. STORAGE BATTERIES. 145 The negative plates as a general rule, do not need renewals, but the positive plates are often subject to repairs which cost at least io% per annum of the original cost of the cell. In many cases of train lighting, the positive plates last but a year on an average, but this service is very severe. The connections between the batteries and in fact, all corrodible parts of the battery plant should be liberally treated with asphalt paint. All connections should be made in a strong and servicable manner and unusual care taken in insulating all parts of a battery which is to be charged from a high voltage constant cuirent circuit. When charging from a constant potential circuit, a resis- tance is usually put in series with a set of cells, so as to keep the charging current uniform. An automatic safety cutout should also be provided, so as to cut out the batteries in case of a dynamo being stopped w^hile connected to the storage batteries, for if this was not done, the dynamo would be supplied with current and run as a motor. A shunt wound dynamo is better adapted to storage battery charging, than the series wound dynamo for several reasons one reason being, that it is not easily reversed by failure of cutouts working, etc. Although we have spoken of the lead type of stor- age battery only, there are several other types which are worthy of considerable study. One of these is called the * 'alkaline' ' accumulator, and has for its positive plates, a mass of finely divided copper surrounded by a copper wire gauze which holds the copper in position. The plates are then placed in an iron containing cell, which is so constructed that iron partitions come between the 146 STORAGE BATTERIES. positive plates, but are held away from them. The solu- tion used is one in which potash is dissolved and before the cell is ready for use, a quantity of zinc is dissolved in the solution and held in suspension in it. When the battery is charged, the zinc is deposited on the iron case and partitions between the positive plates, and the cop- per in the positive plates is oxydized and the electro motive force of the cell will be found to be about ^q volts, much lower than the lead types of battery. When the cell is discharged, the copper oxide is reduced and the zinc on the iron partitions is again dissolved in the pot- ash solution. Although the voltage of the cell is low, its current capacity is high and a cell capable of furnishing about 300 watt hours, w^ill weigh but }4 as much as the usual lead cell. The K. M. F. of this type of cell is quite constant and owing to its small weight and size as com- pared to the same capacity of lead cell, its application to street car propulsion is to be watched with interest. The Edison storage battery has recently appeared as a com- mercial article. Its chief advantage over the lead cell is that it is light and compact and may readily be adapted to traction work. The jar in which the elements are retained is made of nickel plated sheet steel. The electrolyte is a 21 per cent solu- tion of potassium hydroxide. The negative plate consists of iron oxide contained in small receptacles on a metal plate, and the positive plate consists of nickel hydrate contained in small steel tubes held together by a steel frame work. On first charging, the iron oxide is broken up ; the oxygen uniting with the nickel hydrate of the positive plate, forming a higher oxide of nickel. On discharging the reverse is true, that is, the nickel oxide is changed to a lower oxide ; the oxygen uniting with the iron oxide of the negative plate. The voltage is 1.5 volts, and the Edison cell with the same watt hour capacity weighs one half as much as a lead cell. STORAGE BATTERIES. I47 Storage batteries cannot be charged by means of the alternating current, a fact which is at once evident when it is remembered that with the current reversing its direction many times a second, a chemical action such as is necessary in any storage battery, would be out of the question. It will thus be seen that the storage battery of any type will always be used in connection with direct current stations, and their value is now becoming gener- ally known in America and Europe. There are many electric light stations supplying low pressure direct cur- rent for incandescent lamps, etc., in large cities where current must be supplied at all hours of the day or night. In such a station it will usually be found that during the brightest hours of the day and between mid- night and morning, that the load on the station is very light, so light in fact that the smallest dynamos and engines in the station may be under-loaded. We will find in many such cases as this, that a set of storage batteries may be installed and effect quite a sav- ing in the operating expenses of such a plant. During the hours of the day when the load is smallest, the stor- age batteries may be charged. Then as the heavy load comes during the early hours of the evening, the batter ies may be connected so as to help furnish current to the circuit and later after the load has lessened to the capac- ity of the battery, the engines and dynamos may be stopped, and the batteries will furnish the necessary current until morning, when the dynamos are started to carry the daily load. Thus the running hours of the station are not only shortened, but as the dyaamos, dur- ing the day, are carrying a load nearer their maximum, both the engines and dynamos should operate at a higher 148 STORAGE BATTERI^. efficiency. By this means, a considerable saving can often be eflfected, and many central stations and office buildings having their own plants, are now using storage batteries to obtain these results. By means of the storage battery, a smaller dynamo may be made to furnish current for a much larger num- ber of lamps, for a limited time, than it would be able to carry alone. This is well illustrated in the electric lighting plants installed on some of the steam railroad trains in America. A dynamo, direct connected to a high speed steam engine has a maximum capacity of about 80 amperes at 70 to 80 volts pressure. The incan- descent lamps used are 16 candle power and are about 200 in number on a six car train and require about 150 amperes at 64 volts pressure. It will tbus be seen that the lamps on the train require 150 amperes of current of which the dynamo can supply but 80, when working at its full capacity, and since the engine drivino: the dynamo gets its supply of steam from the locomotive, it is often impossible to get any steam at all in certain sections of the road when all the steam in the boiler must be used to operate the locomotive in pulling the train. Thus it will be seen that to maintain a reliable light, a storage battery is the only means which can be used to obtain good results, under such conditions. In practice 32 cells of 150 ampere hour batteries of the lead type, are generally placed under each car and their voltage w411 thus be found to be about 64 volts for the set of 32 cells. The dynamo is run continuously, except at such times as the locomotive is disconnected or steam cannot be obtained for other reasons and in this way the batter- STORAGE BATTERIES 149 ies are always in condition to supply the current needed in addition to that from the dynamos. Train light- ing service is very severe and much time and money has been spent in developing practical and successful sys- tems of train lighting. Probably the greatest appli- cation of the storage battery — both the lead cell and the Edison cell — is to the elect ric Figure 38. — typical storaae battery. carnage. The car- riage is propelled by a small motor. The chief advantage of the application of electricity to the carriage is the ease with which the carriage may be controlled. By means of a set of storage batteries from the usual arc lighting circuits of constant current type, incandes- cent lamps may easily be operated on the usual multiple plan. This would hardly be an advisable thing to do I50 STORAGE BATTERIES. however, in residence lighting, unless an automatic device prevented the incandescent lamp circuit from being thrown on while the high voltage arc light circuit was charging the cells, for otherwise the handling of the sockets and incandescent lamps might be a dangerous thing to do. The storage battery has also been used to a large ex- tent for operating small motors in phonographs and other automatic machines. Their use in medical and surgical work is also quite general. The application of the storage battery to street railway work is at present far from general, but as suggested in previous chapter, the storage battery system is an ideal one and a fortune awaits the successful investigator in this line. A few points in regard to the care of the usual lead type of accumulator, in addition to those already men- tioned, may be of value to those charging or handling them. Storage battery plates are usually received from the makers after having been formed, and, after having placed the plates in position in their rubber or glass cells and having taken due care in seeing that the positive and negative plates do not come in contact with each other, they should be covered with acid solution of about 1. 17 specific gravity and allowed to stand until the solu- tion has thoroughly entered the pores in the plates. The lead connecting lugs leading up from the positive and negative plates, should be painted with an asphalt paint to keep the acid from attacking the bolts and nuts usually used to connect one cell to another. Care should be taken to scrape the contact surfaces of the lugs and con- \ STORAGE BATTKRIKS. 151 nectioiis between the cells, and thus reduce all ueedless resistance between the batteries. After a connection h^is been made, it should be painted with an acid and water proof paint or varnish, to prevent corrosion. The cells are connected in series. The positive plate of one cell connected to the negative plates of the next cell and so on. If the battery is to be charged from a constant potential circuit, care must be taken to allow but a safe amount of current to pass through the battery. The amount of current w411 depend on the counter K. M. F. of the cells and their resistance. Thus if we are to charge from a no volt circuit, we may safely charge from 50 to 55 cells in series, each of the two volts K. M. F. A resistance should always be placed in series w^ith the set of batteries in such cases and in this way be varied to keep the charging current uniform. The amount of current that 1 10 volts will put through, say, 50 cells will depend of course on Ohms law. K C= — R But K or the number of volts, will be the difference between the counter B. M. F. of the set of batteries and the 1 10 volt circuit. Thus the voltage of the 50 cells may be 100 volts, in which case E=io or the difference between 100 and no. R or the resistance is likely very low, probably not over | ohm, and thus 10 C= — or 50 1 5 which in a cell whose maximum charging rate is but 25 or 30, will be too much. The only way to prevent this excessive flow of current, is to either add extra cells to 152 STORAGE BA'TTERIES. the set or place a variable resistance in series with the set of batteries. The larger the size of the plates and the more their number in a s^iven cell, the lower its resis- tance will be. Knowing the charging and discharging rate of a given battery, and also its voltage and capacity in ampere hours, any problem in the application of the storage battery, may be worked out. New cells should receive several long and steady charges before being put on regular heavy work. The number of amperes multi- plied by the number of hours charged, will give the ampere hour charge and new plates after having been dried out in shipment, should be carefullv charged the first few times. - A cell should never be allowed to discharge lower than 1.80 or 1.85 volts, and under no condition should a dis- charged cell be allowed to stand any length of time with- out recharging, for the plates are likely to become coated with a white coating of ''sulphate" which not only injures the plates, but can only be removed hy a most careful and tedious process of charging at a low rate. Buckled cells caused by short circuits or heavy charg- ing or discharging, should be taken apart and straight- ened by mechanical means. A heavy deposit of active material or *'mud" may be found in the bottom of a retaining cell and may be enough to short circuit the bottom of the plates. Rubber gloves should be used in handling the plates and solution, and woolen clothing should be w^orn, for cotton goods are soon destroyed by splashes of battery solution. Ammonia may be applied to discolored cloth and will often counteract the eflfect of the acid. Great care should be exercised in mixing the sulphuric STORAGE BATTERIES. ^53 acid and water. The acid should be poured in the water in small quantities and should be stirred well as it is being mixed. Considerable heat is always generated under such conditions, and the acid should be allowed to cool before passing over the battery plates. ^ 154 HEATING AND METAI, WORKING. CHAPTER XI. KI.ECTRIC HEATING AND METAI. WORKING. STATION INSTRUMENTS. Electric heating is a subject that at present is interest- ing many able workers in the electrical field. Its advan- tages over coal or gas for heating are many, and its only drawback is its cost when current at the usual lighting rates is used. The principle of all heaters both for direct and alter- nating current is that of passing current through resist- ing conductors which of course consumes energy and ex- hibits itself in heat. The conductors used in the usual heaters for electric street cars, are generally made of Ger- man silver or iron wires, and these wires are in most cases surrounded by some insulating material which is a good conductor of heat, such as fire clay, sand, or enamel c This material really furnishes the wire with a larger heat radiating capacity. It will be evident, for example, that if a heated wire is placed against a plate of cold glass that it will at once lower its temperature and gradually raise the temperature of the glass. The wire cannot in this case be raised to a dangerous temperature without passing through it several times the amount of current that would melt it in open air. The wires in the usual electric heater, thus carry a much greater amount of cur- HEATING AND METAI. WORKING. I55 rent without being over-heated, than would be possible without the radiating material surrounding the wire. In one form of heater, the wires are fastened to an iron plate by means of enamel, the enamel not only complete- ly covering the wires and uniting them to the iron backing but also insulating them from the iron. The wire is in intimate contact with the iron plate by means of the enamel, and of course cannot become much hotter than the iron plates, which having considerable radiating surface, make efficient electric heaters. One of the earliest forms of electric heaters, patented in the United States, used iron or German silver wires imbedded in fire clay, the whole being incased in an iron box. This form of heater was used in the earliest elec- tric street railway put before the public. There are to-day about 200 patents on various forms of electric heating and cooking devices. The usual form of electric street car heater, takes from two to five amperes at 500 volts pressure, and after a street car is once heated, from 1200 to 1500 watts of current will provide enough heat for the coldest weather. In a large electric street railway plant, the current will cost about three cents an hour per car to keep the heaters in operation, and this figure will be found to be little if any more than stoves using anthracite coal for fuel. The heaters are usually placed under the seats and are of course out of the way of passengers. A large number of street railways are now using them. Cooking by means of electricity is being advocated by several companies and without doubt there are many cases where electric cooking devices can be used at a cost of operating about on a par with coal stoves. IU6 HKATING AND METAI. WORKING. Quite a number of patents have been taken out on heaters designed for alternating current work whose operation depends on the setting up of eddy or secondary currents in cores of coils of wire carrying alternating current. Such a heater would not of course operate on direct current circuits. One of the most interesting applications of heat from electricity is that of metal working and welding. Electric welding machines are at present doing work that would have been practically impossible with forge and hammer. The Thomson electric welding machines use alternating current for welding purposes by sending an alternating current of moderately high pressure through the primary coil of a large converter, the sec- ondary of which furnishes a current of immense volume at a voltage of but a few volts. The pieces of metal to be united in the weld are placed in the secondary circuit by means of clamps, with their ends in contact with each other. The point of contact being the only appreciable resistance in the secondary circuit, the ends are at once raised to a high temperature. The cur- rent is then increased in the primary, and the junction of the two pieces of metal to be welded, is raised to a welding heat. While this heating is in progress, pres- sure is being applied so as to press the pieces to be welded into even more intimate contact. The whole operation of welding a large bar of iron occupies but a few seconds and the joint made, in many cases is found to be the strongest part of the bar. Many metals may be welded in this way which are very difficult or practicall y impossible to weld in any other way. Wrought iron pipe bent in various awkward shapes, may be united in this STATION INSTRUMENTS. 157 way in a perfect manner, an operation which is often- times very expensive when done in the usual manner. Large crossing frogs and steel rails are often welded on the electrical welder. The intense heat of the voltaic arc is used to some extent in metal working. The usual plan is to make the metal on which the work is to be done, one pole, and a carbon provided with a flexible conducting cord and handle as the other pole, and form the arc between the metal body and the carbon. If a piece of metal be connected to one pole of a suitable source of current supply, and a pail of salt water be con nected to the other, it will be found that by dipping the end of the metal in the water that it may be raised to a wliite heat in a few minutes, the water still remaining cool. Tliis may seem impossible at first thought, but neverthe- less a fact. A large number of small arcs probably form between the metal and the water, and with metal pieces of proper size, they may be quickly raised to a high heat SWITCH BOARD AND STATION INSTRUMENTS. All electrical machinery should, when performing its usual duty, be capable of being controlled, started and stopped in an exact and simple manner, and to know whether a given dynamo or motor is performing its duty, there must necessarily be connected suitable measuring instruments. The proper fitting of a station switchboard is an extremely important consideration, for in many cases, without the use of simple and reliable means of dynamo regulation and control, a station could never perform its proper work. What we cannot see being devel- oped in machinery, we must have indicated by some means. 158 STATION INSTRUMENTS. Bvery electric light or power station should be provid- ed with all instruments that are necessary for the gov- erning and regulating of its machinery. Ihere should be instruments which indicate the an.ount of load on the dynamos in amperes, also their p:essure in volts. The dynamo regulating apparatus may be either auto- matic or performed by means of rheostats, etc. Ground detectors should be used to detect or locate contacts between the wiring or dynamos and the ground. To prevent damage from lighting in the station, lighting arresters are placed on the lines exposed. Switches should be provided to connect the dynamos to the cir- cuits or to make various combinations of the dynamos and thus get various currents. Fuse or magnetic cutouts are used to prevent a load being applied to the dynamos beyond their maximum capacities. The switch boards themselves should be made of a non-combustible insulating material, such as marble or slate free from metallic veins, marble being the best possible material usually, for it has high insulating qualities and does not crack or chip as easily as the usual grade of slate generally used. "Marbleized" slate how- ever, is much superior to the usual slate and is larg^ely used. In the score of economy, wooden switch boards are often placed in otherwise first class plants. An oak or pine switch board in a plant using low voltage cur- rent, may undoubtedly be made reasonably safe, but it is an exceptional case when one is found, and as a rule a wooden switch board for high potential circuits, when made safe, will cost nearly as much as a slate or marble board. STATION INSTRUMENTS. 159 There should always be from two to three feet space behind a switch board and it should be kept free from waste material from the plant. Station electricians often pile or throw everything imaginable behind them and when trouble comes behind the board, it is a hard job to do anything in a quick manner. Many of the larger electric light companies are building and selling very superior switch boards at reasonable figures. Rheostats or Field regulators used with shunt or com- pound wound dynamos provide means of regulating their output by varying the current through the field windings. They usually consist of a series of resistances in the form of German silver or iron wire coils that are connected at several points to contacts on the face of the rheostat, and by means of a contact brush rubbing on their surfaces^ more or less resistance is put in series with the dynamo field circuit. Rheostats of this description are very clumsy, and a better type now produced, is the enamel or cement rheo- stat in which the resistance wires are imbedded in cement or enamel, only a small amount of wire being required, and that very small in size, as it is well known that a wire imbedded in such a manner will carry a current Several times greater than in open air. They occupy but little room and are compact and fire proof. Quite often in central stations where circuits are une- qually loaded, it becomes necessary to raise the potential on individual feeders. To increase the potential of the dynamo would not sufi&ce because circuits having a light load would have too high a pressure. The **booster" for direct current circuits consist of a small series dynamo placed in series with the circuit whose pressure is to be l6o STATION INSTRUMENTS. raised. The conductors on its fields and armature are sufficiently large enough to carry full current. An increase of current in the series field would mean an increase in potential at the armature and this added to the potential of the generator gives the desirable pres- sure. This machine increases the pressure automatically as the current increases. For alternating circuits, this scheme is not possible, but the flexibility of the transformers is admirably utilized by Mr. L. B. Stillwell in the Stillwell regulator and described by him as follows: '*If each supply circuit receives current from an independent generator, that is, a generator which is called upon to furnish current to other supply circuits, the necessary adjustment of pressure is obtained by regulating the field charge of the generator by means of the rheostat provided for that purpose. If however, several supply circuits are receiv- ing current from the same generator, it becomes neces- saiy to provide means for adjusting the pressure of each without disturbing the others. The regulator consists of a transformer having a secondary coil adjustable in length. Connections are brought out from dififerent points on the secondary coil, to a multi point switch, by means of which the secondary coil, or any portion of it^ may at will, be thrown in series with the supply circuit. When this is done, the electro-motive force due to the whole or a part of the secondary coil of the regulator is added to the initial potential of the circuit. The potential of tbe supply circuit may therefore be acurately adjusted, independent of whatever may be the potential at the terminals of the generator". An instrument, the Compensator, is always used with STATION INSTRUMENTS. l6l the regulator and in the same circuit. It consists of a small transformer which supplies current to the volt- meter. The primary circuit has two windings, one of which is on the usual high pressure constant potential circuit and the other is a winding in series with the circuit whose voltage is to be measured. The secondary circuit supplies current to the voltmeter and when current is flowing, a current is induced on the secondary coil from the primary, which causes voltage to be shown at the voltmeter, corresponding correctly to the voltage at the end of the line with that current. To sum it up, the compensator acts upon the voltmeter to give the potential at the end of the line. Voltmeters and ammeters are of two general t3rpes, those whose reading is due to magnetic effects and those whose reading depends on the expansion and contraction of a wire due to current passing through, and heating it. The measuring instruments using magnetism, are of various types, some of them using a simple selonoid of wire acting on a movable iron core, to which is attached the indicating pointer. In instruments of this type for use on alternating current, the selonoid spool, if made of metal, is always slit to prevent the spool acting as a sec- ondary coil of low resistance, in which currents would be generated by the passage of current through the coil windings. The iron core of such a coil would have to be laminated, or built up of small iron wires to prevent cur- rents being generated in it. Other magnetic instruments use the effect obtained by mounting a small armature between the pole pieces of a permanent horse-shoe magnet, and sending the current to be measured through the armature, which tends to I62 STATION INSTRUMENTS. revolve on its shaft and thus produce a movement which gives the reading. Such instruments are usually pro* vided with jeweled bearings and are quite expensive, biv the leading measixring instruments of this type, the Weston ammeters and voltmeters, are the standard instru- ments to-day in America for direct current measuring. The *'hot wire" instruments are mainly used for alter- nating current work, for since the heating effect of a given current is the same for either direct or alternating current, it follows that such an instrument should be well adapted to the measurement of alternating current. All high grade instruments should be very carefully handled and in case repairs are needed, it should be done only by one thoroughly acquainted with the work. The rougher classes of cheap instruments are ofted found to be incorrect and it is always policy to calibrate them by means of a standard instrument as often as possible. In selecting a switch board ammeter or voltmeter, an illuminated scale with large figures is preferable. Dead- beat instruments should be used as much as possible as an instrument whose pointer comes at once to the correct reading and stays there without needless swinging, saves time, and is by far preferable to those whose needle swings to and fro before coming to the exact reading. All instruments should be placed in such a position as to be easily seen by the dynamo tender, but should not be placed in such close proximity to a dyna- mo, as to have its magnetism effect the reading. In case of it being impossible to place them away from the vicin- ity of a dynamo, they should be provided with magnetic shields, which may be made in various forms. Voltmeters should be chosen having as high a resi»- STATION INSTRUMENTS. 1 63 tance as possible, and ammeters should have the least possible resistance, for it will be found that station instruments often take many times more current to operate them than should be used on proper instruments. In placing instruments on a switch board, care should be taken to so place them that their needles or pointers will be at zero when no current is flowing. Direct read- ing instruments are always to be preferred to those read- ing in * 'degrees", etc. A voltmeter should read directly in volts, and an ammeter in amperes, or a resistance measuring instrument in ohms. All electric light or power stations having conductors in the open air, must have devices to protect the dynamos from injury from lightning. It should not be understood that lightning must actually strike a line to injure the apparatus connected to it. The majority of cases of trouble from lightning occur from currents of high volt- age induced in the line by the passage of lightning through the air near or parallel to the line. The voltage is generally very high, and ruined armatures and field coils result unless means for protection are employed. In many cases the actual damage to the dynamo is caused by the dynamo current following the high voltage lightning discharge, and the damage is done before the dynamo can be stopped. A great deal of time and ingen- uity has been spent in devising various lightning arrest- ers. To be^ reliable, a lightning arrester should always be ready to operate. It should allow the lightning to pass to the groimd, but at the same time prevent the dy- namo current following. The lightning takes the path of least resistance to ground and will of course break tnrough the system at its weakest point. 164 STATION INSTRUMENTS The term resistance'* as here used does not necessar ily mean the ohmic resistance but the sum of the ohmic resistance and the impedance due to the self-induction of the circuit. A lightning discharge rather than pass through a coil of even very low resistance will often jump a large air gap and pass to the ground. The lightning arrester usually places a small air gap between the systems and the ground, and this is designed to be the path of least resistance to ground. After a dis- charge takes place across the air gap to ground the next operation is to interrupt the dynamo current which we have said, usually follows. This is accomplished in various ways, one of the most common being to place the air gap near the poles of a small electro magnet, which ** blows'* out the arc by means of the magnetism, it being a well known fact that if a magnet is placed near an arc so that the arc is in the magnetic field that the arc will be apparently blown aside as if it were in a strong current of air. By using a strong magnetic field in this way, an arc may be instantly inter- rupted and blown out. Another method is to have the air gap over which the arc would i*tart, inclosed in an air tight box and as soon as an arc 1:1 started, the confined air immediately expands due to the heat of the arc, and operates suitable mechanism for breaking the circuit. The air gap may be made between two terminals made of non arcing metal and thus make it impossible to main- tain an arc. The non-arcing metal is an alloy lately dis- covered which apparently on being melted by the arc. forms a gas having a high resistance, for a few small air gaps in series between pieces of this alloy, will rupture an arc on the highest pressure used for commercial eieC' trie lightin|?5. " T-i CO -^ 00 00 «0 "^ CC ^ rl rH C<1 M TtH T-1C0t-i-tO0 1-1 GO O t- «0 iC ^ T-1 ^ CO CO »0 t- 05 tH N CO ?D t- T-H iC C30 2^ Oi-i 05 Tt 00 «0 CO OJ N «0C00JNQiClr-O(M tHCO'*0000«O^COt-I i-lrHOClCO'* i-tC0t-lO'r-lt-00iOt-lO'*0^ THCOTtit^O^iCCO^oi 1—1 T-i OiCC CO OiOOCOCO. OCt-lOrH05CO?OOCO 1— ICOb-'^i-nCt-i-(?CO50C i-iOClCOiCt-O'rt't- So > l-H (M '^ I- 1-1 '^ ^►5 ! t- »C Ct Ci N OC I- lO O > COCOCOCON OiOCt-TfiOiCOCOCO?© o^cob--^o5t-Ci'rtnn»ot^i-HT*Ia6 « z : r-icot'iOi-^t-oDiCi— ic-^o;i i-iCOrtftr-05iOCOi-iOi 1—1 1—1 05 CO CO ?ocot- ODl-'!t CSCiOCt- T-ICOi-^C. -^-t'OSOiCOOSCO ::^;2;g^^:^ T-tCOSCO^Ol— COOt-"^ 1-1 1-1 (M CO lO «0 00 1— IC0t-'>*OS^-^C»Oi'^O5C0 i-iO^Ttit-TH'^jiOCiost- T-(i-i05NC0 CO^COCONOCOOOOOOO OSOOt-Tj^OSCOCOCOOOiOiiO i-(COt--*t«$5t-Ci'ti-^Ci<:o T-t N CO iO t- 1-1 ^ 00 •pH05C0U300O»0O»O UJ gjt-MiOi 00 00 05U3i— (C* 05 05 OO t- iC 05 05 Tf 05 05 o: c: O: oc o: oc r: I- r-icoicoi-fC505c;o; 1-1 1^ 05 CO 'Tf §1 CO CO CO CO CO 05-^C50Ct-COCOOi:CO:cOiO rlCOiOCi'TtiOOlr-t-^cd 1— (tH05C0'^ OJuOi— I CC t- OOi— 105'^CO OSCOCOt^CO •rH0i^«;05 5HCg^«^g ^ o iCi-lCOt' Oi— l05'^05T**CO00 05COtH i-H'fH 05 rHCOCOCOCO lO i-He5T*Ja>o6oocd'^coo5«oo5 i-H 05 'rt- t- OS CO 00 M 5I CO CO CO CO CO 05Tt<05COt-COC005C005COi i-tCOJOOS'-^OOt-t-f 1-1 th 05 CO' ::?^:s<:^ ^ 93 CO i»«0 9 US O to *i: §'. >2| >^^ uii rt t) S-°e Z^ Sal w bJ ' o ••-• ^ a bflT3 0.2 eo *j CO (U 4> "3 ♦J rt -M tM o a> aju a o rt't; 3° a rt t» a ss eu =J C o ^ be ^*j a COM-- II o o as COPPER WIRE TABLE. Giving weights, lengths and resistances for A. W. G. TBrown and Sharpe) Guage. GUAGE, To the nearest fourth significant digit. 0000 000 00 1 2 3 4 5 6 7 8 9 10 11 12 13 14 16 16 17 .} 30 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 Diam- eter. Inches. 0.460 0.4096 0.3648 0.3249 0.2893 0.2576 0.2294 0.2043 0.1819 0.1620 0.1443 0.1285 0.1144 0.1019 0.09074 0.08081 0.07196 0.06408 0.05707 0.05082 0.04526 0.04030 0.03589 0.03196 0.02846 0.02635 0.02267 0.03010 0.01790 0.01594 0.0142 0.01264 0.01126 0.01003 0.008928 0.007950 0.007080 0.006305 0.005615 0.0050 0.004453 0.003965 0.003531 4010.003145 Area Circu- lar mils. 211,600 167,800 133,100 105,500 83,690 66,370 62,630 41,740 33,100 26 250 20,820 16 510 13,090 10,380 8,234 6,530 5,178 4,107 3,257 2.683 2,048 1,624 1,288 1,022 810.1 642.4 509.5 404.0 320.4 254.1 201.5 159.8 126.7 100.5 79.70 63.21 60.13 39.75 31.62 26.0 19.83 15.72 12.47 9.888 WEIGHT. Iook for Railroad Men. Illustrated. 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