/Sandeivon ^wilci^oard^ for RJletiiaiina-Curteni Povret ^aiioap 1 ,- Switchboards For Alternating-Current Power Stations C. H. Sanderson Switchboards For Alternating-Current Power Stations C. H. Sanderson and H. A. Travers General Engineers, Switchboard and Power Station Design Westinghouse Electric & Mfg. Co. Reprinted (revised) from The Electric Journal Vol. X, No. 1 and Subsequent Issues Westinghouse Electric & Manufacturing Company East Pittsburgh, Pa. Publication 1541-A— 3-16 Digitized by the Internet Archive in 2016 with funding from University of Iliinois Urbana-Champaign Aiternates https://archive.org/details/switchboardsswitOOtrav Qj, “I ~^ rckVY\ *^. 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The following are the assumptions upon which the ultimate breaking capacity of a circuit-breaker are based by a leading manufacturer. Any departure from these will change the relative rating. 1. That the generators have an inherent reactance of approxi- mately 8 per cent or, in other words, give a maximum current on the first wave of short circuit of 12.5 times the root-mean-square full-load current ; and also that the sustained short-circuit current has a maxi- mum value of three times the r.m.s. full-load current. 2. That the current at the time the circuit is opened is approxi- mately 50 per cent of that occurring on the initial wave; or in other words, 6.25 times the r.m.s. full-load current. Current Trans. r-r-r—r-r;:;. H H Feeders -Single Bus System Used for small stations where simplicity and economy are of primary importance. 3. That the circuit-breakers are very close to the generators or other source of power, so that the circuit reactance from the gener- ators through the circuit-breakers to the point of short-circuit is practically negligible. 4. That the operation of the circuit-breakers is normal for the particular tyf)e, and that the method of tripping is that known as “instantaneous”, under which conditions the mechanism should be expected to operate in 0.1 to 0.2 seconds. 5. That the normal operating voltage which the circuit-break- ers are called upon to open is that on which their rating is based. 6. Where a circuit-breaker is used on a lower voltage than the maximum for which it is designed, it is assumed that an increase of approximately 1 per cent in kilovolt-ampere rupturing capacity is permissible for every 1 per cent decrease in operating voltage. The amount of current available in a given circuit under short- circuit conditions is determined by the amount of effective impedance (usually nearly all reactance) in the circuit. Additions to the effec- tive reactance, whether introduced by transmission lines, power 1541 Switchboards For Power Stations 11 transformers, or otherwise, will reduce the available current in direct proportion. When circuit-breakers are to be used on a secondary of a step- down transformer, the kva. capacity of which is small in comparison with that of the source of supply, the reactance of the transformer and its capacity are the factors to be considered in determining the size of breaker to be applied. Oscillograph records show that the first rush of current on a short circuit falls off to approximately two or three times full-load current at the end of one and one-half to two seconds. As this current value is approximately one-half of that assumed to be flowing at the instant an instantaneous trip breaker would open, a circuit- breaker provided with relays having a definite minimum time setting of two or more seconds may be used on a circuit having twice the capacity rating of that breaker when set to trip instantaneously. I^^Current Trans. — 1 I I — — r , 1 i i i . : Tt i i , Bos A Bus B Dis. Sw. Oil Cit Br. V Fig. 6 — Double-bus Single Circuit-Breaker System This arrangement greatly increases the chances for continuity of service over that shown in Fig. 1. One bus-bar may be used as an auxiliary only, or one may feed a lighting load while the other feeds a power load. A non-automatic breaker may be applied on a circuit of twice the capacity of the corresponding automatic instantaneous trip breaker as at least two seconds will elapse before the station attendant can trip the breaker. The breaking capacity of a circuit-breaker may be expressed in terms of the maximum current which the breaker is capable of open- ing successfully at its rated voltage. This maximum value of current which a breaker will open on short circuit at its rated voltage or at any given service voltage may be designated as the ultimate ampere breaking capacity of a breaker and is obtained as follows: (a) Find the current corresponding to the catalogue kva. breaking capacity rating given for the breaker under the voltage required. (b) Multiply this current by 6.25 (the second assumption given above is that the current at the time the circuit is opened, is 50 per cent of that occurring on the initial wave.) 12 Switchboards For Power Stations 1541 If the product thus obtained is less than the current available under short circuit conditions in the circuit on which a breaker is to be applied, a larger circuit-breaker should be selected. This latter basis of rating is the more satisfactory one as it forms a statement of what the breaker is actually capable of doing without reference to the capacity of the power system, method of tripping the breaker, to the short-circuit characteristics of generators and other synchronous apparatus, or to the reactance of apparatus and circuits up to and beyond the breaker to the point where the short circuit occurs. Reactance Coils — By the use of current limiting reactance coils at various points in the system it is possible to use circuit-break- ers having a catalogue rating less than the capacity of the system. It may be advisable in some cases to use the combination of reactance coils and small circuit-breakers rather than a large breaker because of space and cost considerations and also to reduce the strains on all parts of the system due to a great rush of current to a short circuit. Moreover, without the use of the coils there is always present the danger that a heavy short circuit will open up the main circuit- breakers, instead of the individual feeders affected, thus shutting down, possibly, an entire system. It is this elimination of service interruption obtained by the use of reactance coils, cutting out only the feeder affected, which makes for ideal operating conditions. Reactance coils are frequently placed in the generator circuits to limit the flow of current on short circuit and thereby to decrease the harm done to a machine from internal short circuit by the re- maining machines connected to the bus-bars, as well as to limit the station output in case of external short circuit. This disposition of the reactance, however, does not eliminate the drop in voltage on the sys- tem caused by a short circuit, does not provide the maintenance of service feature above mentioned, and does not materially decrease the strains on the circuit-breakers. The ideal location of these coils is shown at A, Fig. 14. If, how- ever, the cost is prohibitive or space will not permit, coils may be located at B, which will protect the group of feeders. The third choice would be to locate them at C or at D. The protection afforded to the apparatus and service is plainly different for the various loca- tions, and each case should be considered individually. Classification of Circuit- Breakers — The usual classification of circuit-breakers in general commercial use is shown in Table I. 1541 Switchboards For Power Stations TABLE I 13 Cost Per Cent Ultimate Volts Amperes Kva. Capacity Type Design Swbd. mtd. or remote 7 4500 200-300 3500 mechanical control 10 13200 300 3000 9 7500 300-500 3500 12 4500 600 3500 Switchboard mounted 13 13200 500 4500 remote mechanical Single frame. Single 17 4500 800 4500 control or electrical- tank for all poles. 30 13200 1200 9000 ly operated 37 7500 1600 8000 43 7500 2000 6000 16 7500 300-500 4000 Swbd. mtd. or remote 20 4500 600 4000 mech. control. Dou- ble Throw 31 22000 300 6000 Swbd. mtd., remote 29 16500 600 8000 mechanical cont. or Single frame. Separate 35 22000 300-600 10000 elec, operated tank for each pole 18 13200 300 6000 18 7500 500 6000 20 4500 600 6000 16 22000 300 16000 ~ 48 16500 600 18000 Remote mechanical Each pole a separate 60 13200 1200 20000 control or electrical- unit with its own 67 7500 1600 24000 ly operated frame and tank. De- 76 4500 2000 30000 signed for wall or pipe 96 750 3000 20000 mounting 55 22000 300-600 40000 67 22000 1200 35000 87 16500 1600-2000 40000 46 22000 300 16000 48 16500 600 18000 60 13200 1200 20000 Remote mechanical 67 7500 1600 24000 control or electrical- Each pole a separate 76 4500 2000 30000 ly operated unit with its own 66 22000 300-600 40000 frame and tank. De- 73 22000 1200 35000 signed for cell mount- 92 16500 1600-2000 40000 ing no 22000 600-1200 80000 152 16500 1600 80000 Electrically operated 160 22000 2000 100000 181 16500 3000-4000 100000 100 15000 600 40000 120 15000 1200 35000 Single frame or base for 139 22000 600 70000 Electrically operated operating mechanism. 168 22000 1200 65000 Separate tank per 175 15000 2000 60000 pole. Cell mounting 280 2500 3000 60000 55 35000 300 17500 61 45000 300 20000 Remote mechanical Each pole a separate 122 70000 300 25000 control or electrical- unit. Designed for 77 45000 300 30000 ly operated pipe frame or floor mounting 90 44000 300-600 40000 125 66000 300-600 50000 Remote mechanical Each pole a separate 195 88000 300-600 50000 control or electrical- unit. Designed for 310 110000 300-600 60000 ly operated open mounting on 620 165000 300 60000 floor 200 22000 1200 200000 Elec. oper. Single base. Separate tanks. Reactance coil per pole. Cell mounting 550 110000 300-600 200000 Elec. oper. Each pole a separate unit. Reactance coil per pole. Designed for open mounting on floor ^Approximate relative cost for 3-pole circuit-breakers without relays or transformers, t Refer to page 10 for assumptions upon which the kilovolt-ampere ratings are based. The last two designs given in the above table are known as the reactance type breakers. Their great ultimate breaking capacity is obtained by opening the circuit on reactance coils, by means of an auxiliary contact, just before the main contacts open. There is no apparent reason why this type of circuit-breaker cannot, by properly proportioning the reactance, be made to open any capacity safely. 14 Switchboards For Power Stations 1541 Rating of Switchboards — The capacity which a switchboard will safely handle depends upon the capacity of the circuit-breakers employed, and the association of the various items, circuit-breakers, bus-bars, instrument transformers, interconnections, etc., which comprise the switch equipment. Experience has demonstrated that there are certain limits of capacity above which automatic cir- cuit-breakers should not be mounted directly on switchboards. These limits vary considerably, according to the conditions of the — r — T — — T — — T — ~T ^ 1 18 Switchboards For Power Stations 1541 required, the watthour meter measuring the station output will still be working at maximum accuracy. The daily load curve may indi- cate that the output is fairly constant over a continuous period. A totalizing watthour meter may then be used to advantage. If the feeders supply different sections of a factory or different factories, or separate communities, a watthour meter should be used for each. The class of attendants in charge of the switchboard deter- mines, to a very great degree, how many and what kind and class of Outgoing Lines Outgoing Lines Outgoing Line? Low-tension disconnecting switches permit the connection of a generator direct to a transformer (with or without connection to bus-bar), connection of generator to bus-bar with transformer dead or connection of transformer to bus-bar with generator dead. This scheme is similar to that used at the Post Falls Station of the Washington Water Power Company, 2300-66000 volts. A generator, transformer, or feeder may be taken out of service for the examination or repair of its circuit-breaker. All apparatus may be in service while the load is removed from either section of either bus-bar for repairs or additions. instruments should be selected. Instruments which are not used, and which are not kept in calibration, are often worse than none at all, as they only take up valuable space, confuse the operator and complicate the wiring. The more simple the equipment throughout an installation the better the results obtained. It should be the engineer’s rule, for stations of this class, not to use apparatus in con- nection with the switchboard which is not actually necessary to the 1541 Switchboards For Power Stations 19 safe operation of the station. On the other hand, this rule does not hold for the larger stations, whose operation is entrusted to trained engineers, for they usually justify the use of many of the finer instru- ments by producing and maintaining, with such an equipment, a highly efficient power station. As a guide to the selection of a suitable equipment the following panel schedules are presented : Outgoing Lines Outgoing Lines Fig. 13 — Single Low-Tension Transfer Bus, Double High-Tension Bus With this scheme, used by the Rio Janeiro Tramways, Light & Power Company, the station may be operated in four separate parts, if desired, any or all of which may be connected together at will. The double-throw high-tension disconnecting switches prevent interconnecting the high-tension bus-bars except by means of the tie breakers. The low-tension connections make it possible to connect a generator directly to its trans- former or to any other transformer through the transfer bus. Alternating-Current Generator Panel One alternating-current ammeter (where phases are likely to be unbalanced an ammeter is often supplied for each phase, or current transformers and amme- ter switch provided for connecting the single ammeter to any phase). One alternating-current voltmeter (or a voltmeter receptacle and plug to connect to station voltmeter). 20 Switchboards For Power Stations 1541 One direct-current ammeter — for alternating-current generator field (optional) ‘ One indicating wattmeter (optional). One power factor meter (optional). One frequency meter (optional). One ground detector (optional; one ground detector is usually connected to each set of main bus-bars where there are two or more generators). One field discharge switch. One controller for engine or waterwheel governor (optional and only supplied when; engine governor is controlled at the switchboard in synchronizing). One rheostat for generator field (usually supplied with generator). One rheostat for exciter field — required only when generator has its own separate exciter (usually supplied with exciter). One synchronizing outfit (not required if but one generator is to be installed which is not to operate in parallel with an outside source of power). One non-automatic switch or circuit-breaker for main circuit. Necessary current and potential transformers. Discussion Field ammeters are considered almost indispensable by most operators, as they assist in properly adjusting the field so that the machine will take its load. All generators are more efficient with the field adjusted to a certain value, as determined by their design. The field ammeters enable the operator to make this adjustment accurately at all times. They indicate the presence of cross-currents between machines, and also assist materially in locating any trouble which may occur at the generator. Machines operating in parallel should have either field ammeters or indicating wattmeters, preferably both, for indicating proper operating conditions. Indicating wattmeters while directly indicating the output of each machine will show what portion of the load is carried by each generator. This cannot be determined by means of the ammeters and voltmeters alone, as they do not take into account the power- factor of the circuit. Power factor meters also indicate, but in a different manner, how the generators are dividing the load. In combination with the ammeters and voltmeters they will permit the ready calculation of the load in watts. They also guide the attendant in adjusting the field excitation to obtain the best results. Power factor meters are sometimes used in place of indicating wattmeters. Voltage readings for the generators are usually taken by means of the “machine” voltmeter, which is usually mounted on a swinging bracket at the end of the board, and the voltmeter receptacles on the individual panels. Most operators require a second voltmeter mounted on the same bracket with the machine voltmeter and con- nected permanently to the bus-bar. This arrangement permits a 1541 Switchboards For Power Stations 21 simultaneous comparison of the bus-bar and machine voltages when synchronizing. The synchronizing outfit may consist of synchronizing recep- tacles with lamps, or with synchroscope, or both. The most popular practice is to place the synchroscope with two synchronizing lamps on a swinging bracket beneath the two voltmeters, where the entire combination may be seen at a glance while synchronizing. Frequency meters are an aid in synchronizing, as they indicate the speed of the generator. They are often used as one of the indi- Feedcrs Feeders mu mu mu mu Fig. 14 — Sectionalized Generator and Main Feeder Bus System With Group Feeder Bus By this system great flexibility may be obtained for large stations feeding a thickly settled community at generator voltage. The station may be operated in halves or any feeder or group of feeders may be served from either half. Similar connections are used by the Cleveland Electric Illuminating Company. vidual panel instruments with large generators, but otherwise but one station frequency meter is supplied. Where there are two or more sets of bus-bars, or several stations feeding into a common transmission line their use is often of vital importance. Watthour meters are not commonly placed on generator panels. They are usually applied to the feeder circuits, but a load totalizing watthour meter is also often employed when it can be conveniently applied. They are, however, sometimes used to record the output of the individual generators. Relays are seldom used with generator circuits except to pro- tect against reverse power, which would motor the unit and per- 22 Switchboards For Power Stations 1541 haps injure the prime mover. Sometimes, however, overload relays are used to indicate excessive load by operating a signal. Under- load relays may be used in a similar manner. »4>~n I Lightning: ^ V^Coil! 2. Arrester rh rU rU. rh, Dis. Sw. Oil Cir. E Dis. Sw. Fig. 15 — Single Sectionalized Low-Tension Bus, With Two High-Tension Buses, One of Which Is Sectionalized The station may be operated as four complete units (generator, transformer, and line separate), or any generator may feed any bank of transformers through the low-ten - sion bus-bar. The step-down transformer for local or station service permits the low- tension bus-bar and circuit-breakers to be taken out of service entirely without inter- fering with the load. This scheme is used by the Washington Power Company, Little Falls Station. Feeder Panels for Motor or Power Service One alternating-current ammeter (ammeter switch or one ammeter per phase may be used if phases are unbalanced). One watthour meter (optional). One automatic overload circuit-breaker. One relay (optional). Necessary current and potential transformers. Discussion Unless it is desired to have the circuit-breaker trip instantane- ously at a certain predetermined overload, an inverse time limit or definite time-limit relay should be applied. Many elect rically-oper- 1541 Switchboards For Power Stations 23 ated circuit-breakers, especially of the higher capacities, require some form of relay to render them automatic. Load Panel Any or all of the following instruments may be placed on the load panel, and most of them can be obtained in the graphic record- ing type if desired : — Watthour meter, voltmeter, ammeter, indicat- ing wattmeter, frequency meter, synchroscope, power factor meter, or static ground detector. Sometimes the generator voltage regula- tor, when used, is placed on the load panel, especially when there is sufficient space available which would otherwise be vacant. utum iuum mum Fi^. 16 — Single Bus Feeder Group System This arrangement is suitable for stations employing large units, each supplying a number of feeders. Each unit and its group of feeders may be operated independently or all may be operated from one main bus. This arrangement is used by the Common- wealth Edison Company, Chicago, at its Quarry Street Station. Synchronous Motor Panel One alternating-current ammeter. One direct-current field ammeter. One indicating wattmeter (optional). One power factor meter (optional). One field rheostat (usually supplied with motor). One field discharge switch (may be omitted when motor has a direct-connected exciter). One synchronizing outfit (not required if motor is self-starting). One automatic overload oil circuit-breaker. One relay (optional). Necessary current and potential transformers. 24 Switchboards For Power Stations 1541 Discussion But one ammeter will be required for this panel, as there should be the same current in each phase. The field ammeter is of great assistance in making a proper adjustment of the field to meet the desired conditions. Its importance is further increased by the fact that motor guarantees are usually based on a certain definite field current. .The indicating wattmeter or power factor meter, as in the case of the generator, will assist the operator to adjust the field properly so that the motor will take its proper load. An indicating 1 J j i j 1 i By this system all groups may be operated either independently or in parallel. The large transformers may have the capacity of two or more generators. A number of dupli- cate lines of different characteristics may be taken from the same power station. This is the arrangement used by the Mt. Hood Railway & Power Company. wattmeter when connected properly by means of a suitable switching device to its transformers will read true watts with the switch thrown one way and the wattless volt-amperes when thrown the other way. The field switch is made double throw for machines which start as induction motors to permit short-circuiting the field during start- ing. The same machine, however, when equipped with a direct- connected exciter need not be provided with a field switch, as the field is short-circuited across the exciter armature when the field switch is closed. If a field switch is provided it may be single throw. 1541 Sivitch boards For Power Stations 25 When the motor is not self-starting the usual single-throw circuit-breaker may be used. When it is started from taps on its own power transformers a double-throw circuit-breaker, automatic on the running side only, is used. When auto-transformers are employed for starting, a special double-throw auto-starter switch, automatic only on the running side and with provision for discon- necting the auto- transformers from the source of power, is used. For very large motors, and for motors connected close to large generating stations, three interlocked circuit-breakers are usually employed ; one automatic, for connecting the machine to the source of power, one for starting, and one for disconnecting the auto-trans- formers. Line Panels For Transmission Lines to Sub-Stations or Tie Lines to Other Power Stations. One ammeter per phase (or one ammeter with polyphase switching device). One indicating wattmeter (optional). One power factor meter (optional), or One reactive factor meter (optional). One voltmeter, or voltmeter receptacle (optional). One watthour meter (optional). One synchronizing outfit (required only for tie line). One automatic circuit-breaker. One relay (optional). Necessary current and potential transformers. Discussion Three ammeters are usually considered necessary, particularly for overhead lines, as they not only give a direct indication of unbal- ancing of the load, but also of any trouble which may occur on any phase. Power-factor meters are very commonly used on these panels as an efficient system should operate at high power factor, and the instruments will indicate those parts of the system which require modifications of their load to better the power factor which in turn reduces unnecessary line losses. Voltmeters may be compensated to read the voltage obtaining at the end of, or at some point along the transmission line. For tie lines the voltmeter is useful in synchronizing with other stations. The voltmeter receptacle may be used instead, to read the potential by means of one of the station voltmeters. Where power may be taken over the line in either direction the indicating wattmeter should be double reading and two watthour meters provided, connected to record power in opposite directions, and so arranged that the mechanism will not reverse. 26 Switchboards For Power Stations 1541 Alternating-Current Rotary Converter Panel One alternating-current ammeter. One reactive factor meter, or One power factor meter (optional). One main automatic inverse-time-limit overload oil circuit-breaker (for high- tension side of transformers). (Equipped with low-voltage release and an auxiliary switch, for tripping breaker on direct-current side of converter). One single-throw knife switch, for synchronizing resistance (required only for converters started by an alternating-current motor using the method requiring synchronizing). One synchronizing outfit (not required when rotary is self-starting from trans- former taps or by means of the self-synchronizing alternating-current motor starting method). One single-throw switch for starting motor when used. One set knife switches (for low-tension side of transformers when rotary is self- starting. Usually mounted on separate starting panel when rotary is over 500 kilowatt capacity). One set of single-throw knife switches (required in main low-tension leads for motor-started converters whose motors connect to the converter transformers) Necessary current and voltage transformers. Discussion Rotary converters are designed to operate most satisfactorily at a certain definite power factor, usually unity, and it is therefore almost necessary that either a reactive factor meter or a power factor meter be used. In operating a shunt-wound converter it is very desirable that the reactive factor be zero (100 per cent power factor). With com- pound-wound converters it is the practice, for average conditions, to operate the converter with shunt field adjusted to give a slightly lagging current in the armature at light loads. With increase of direct-current load the field strength increases to produce a leading current at full load and overloads, and thereby obtain the desired compounding effect. Reactive factor meters are preferable to power factor meters for indicating proper converter operating conditions as they give a more impressive and nearly direct indication of the amount of wattless current; for example a variation in power factor from unity of 2 per cent corresponds to 19.7 per cent reactive factor. It is important in this connection, however, that the reactive factor meter indicate the reactive factor of the rotary, and not of the combination of rotary and transformer bank. To insure this the meter should be connected to transformers on the secondary leads of the power transformers or, if connected on the primary side of the meter, should be calibrated to read the correct reactive factor at the 1541 Switchboards For Power Stations 27 value at which the rotary should normally operate, and should be provided with a calibration curve to enable correct readings to be made at other points on the scale. The proper choice of switching apparatus for converters depends on the scheme of operation, the size of the rotary, the characteristics of the power supply and the nature of the load. Its combinations are so many that space does not permit of a complete discussion. Direct- Current Exciter Panel One direct-current ammeter. One voltmeter (or receptacle to connect to main direct-current voltmeter). One single-pole non-automatic circuit-breaker (optional). One rheostat (usually supplied with exciter). One three-pole main switch (two-pole if for operating singly or if shunt wound) or separate single-pole switches. Two exciters may be controlled from one “double exciter panel’ ’ by adding to the above schedule one ammeter, one rheostat, voltmeter receptacle, and the necessary main switch. Comparative Space Required The self-contained switchboard (Class 1) occupies less space than any other. Its floor plan takes the shape of a long, narrow rect- angle, however, which sometimes involves more valuable space than the shorter boards of Classes 2 and 3, whose switching devices, transformers, and buses may be mounted at a distance from the panel in a less important and probably more favorable location. Frequently it is found that owing to the disposition of the space available for switching equipment a board of Class 2 or 3 must be used, although otherwise a Class 1 board would have answered. Figs. 1, 2 and 3 give an idea of how the same equipment com- pares in space occupied when designed according to the three classi- fications given herein. Fig. 3 has little or no advantage over Fig. 2 in space occupied, but has the advantage that the two parts of Fig. 2, that is, the panels and switching devices, must be within the range of mechanical operation by means of bell-cranks and connect- ing rods, while the two parts of Fig. 3 are, comparatively, unlimited as to location. Comparative Cost The cost of the self-contained board is usually less than that of any other type. The remote-control mechanically-operated board, with switching devices and bus-bars arranged for wall mounting, may be made as cheap, and sometimes even cheaper, as the saving in length of board may neutralize the additional cost of operating 28 Switchboards For Power Stations 1541 mechanism. Assuming the cost of the switchboard shown in Fig. 1 to be 100 per cent, the cost of the same equipment in Fig. 2 would be approximately 115 per cent, and for Fig. 3 would be 140 per cent. In some cases great saving in main cables can be effected by arrangements possible with Class 2 and 3 boards, which may result in reducing the total price of the installation to the same figure, or even less than if the self-contained switchboard were used. 1541 Switchboards For Power Stations 29 II SELF - CONTAINED SWITCHBOARDS OF 6600 VOLTS OR LESS WITH OIL CIRCUIT-BREAK- ERS AND BUS-BARS SUPPORTED FROM THE BACK OF THE PANELS By C. H. SANDERSON The most common generating voltages used for alternating- current power stations of moderate capacity for the usual classes of electric service are 2200 and 6600 volts. The term “moderate capacity,” whem applied either to a generating station or to a single generating unit, conveys a very different meaning now than it did a few years ago. Our moderate capacities of today were then maxi- mum capacities, but the switchboard problems were even more serious ones than those which confront the engineer today. They were then venturing into new and untried fields, while now the results of their pioneering are being perfected. Twenty years ago the self-contained switchboard had the entire field to itself, as there was then no neces- Fig. 1 — Single Bus-Bar System Generators and feeders at opposite ends of bus-bars permitting use of totalizing instrument transformers. sity for any other class. With the advent of 2200 and 6600- volt gen- erators and transformers came many different types of high-voltage airbreak switches, circuit-breakers, and plug receptacles, most of which were expensive, untrustworthy and even dangerous when com- pared with the oil-insulated devices which have replaced them. Application Experience has shown that for the usual conditions of service this class of switchboard should not be applied to stations whose capacity exceeds '""SOOb k.v.a., three phase. Moreover, it is not con- sidered good practice to exceed 6600 volts, and it is usually advisable *70 per cent of this for single-phase; 140 per cent for two-phase. 30 Switchboards For Power Stations 1541 to confine its application to 2500 volts or less. The reason for this limitation lies in the danger to attendants from high-voltage appa- ratus when in close proximity to low voltage control and instrument wiring, rheostats, etc., which require inspection and occasional re- pairs. Also in the necessity, with the higher voltages, of longer and higher switchboards to gain sufficient spacing distances. It is rec- ommended that the size of individual circuit-breakers and switches for this type of switchboard be limited to 800 amperes or less per pole at 2500 volts on account of — a — The advisability of limiting the amount of power handled by one circuit- breaker mounted directly on the panel. b — Difficulty of obtaining adequate insulation distances between the heavy bus-bars and connections required for larger capacities. c — The mechanical strains imposed upon the panels by the larger capacity circuit-breakers with their heavy connections, due both to their dead weight and to the shock of operation. Tot. Cur. Trans Tot. Cur. Trans. Tot. Cur. Trans. Generators Feeders Feeders Generators Fig. 2 — Single Sectionalized Bus-Bar System Station may be operated in halves or as a unit as the load requires. There may be conditions in certain installations where it is advisable to exceed these limits. No hard and fast rule can be made, as few installations are governed by the same conditions. The fol- lowing suggestions, although . applying to all boards of this class, should particularly be followed when the ultimate capacity con- nected to the bus-bars will be greater than the recommended limit: The first consideration is the circuit-breaker. The type chosen should be of rugged design which will carry its rated current continuously with not more than 30 degrees C. rise in temperature on conducting parts and which will not permit the escape of oil, either through leaking, creeping or expulsive effect of short-circuits. It should have a breaking capacity sufficient to rupture, in case of a short circuit, the current sustained after the interval between the first rush of current and the instant at which the breaker is set to open. If rubber-covered wire is used for bus-bars or connections, it should be covered with a flame-proof braid. The panels should be of sufficient width that there will be ample space between adjacent circuit-breakers in which to take away their leads. Instrument transformers should preferably be mounted 1541 Switchboards For Power Stations 31 apart from panels, but when located on rear of switchboard should be rigidly secured to strong brackets to prevent vibrations due to heavy overloads or short- circuits. The bus-bars should be as far apart as the design will conveniently permit and should be located near the top of the board. This arrangement places them out of reach of the attendants, at the same time giving accessibility to the back of the board, and also removes them from the immediate vicinity of the circuit- breakers. Special precautions should be taken to insure that nothing can fall across the bus-bars or connections. Bus-bar screens or suitable insulation or both should be used. Insulation without screens is perhaps sufficient for bus-bars of small cross-section, but heavy capacity bus-bars require ventilation and for them this arrangement should be reversed. Moving parts such as rheostat chains, mechanical connecting rods, etc., should be so arranged that their failure will not entangle other apparatus or cause short-circuits. They should be run in pipes or protected by shields where necessary. Tot. Cur. Trans. Generator and feeders at opposite ends of bus-bars permitting use of totalizing instrument transformers. Choice of System The principal factors influencing the choice of the system are — the nature of the service to be supplied, the size and number of the units to be employed, and the expense justifiable to give continuity of service. Other factors, such as a diversity of apparatus to be controlled or the sequence of purchase, may have considerable influence in the choice and also in the growth of the system. Sim- plicity should be the principal aim. The simplest system which will do the work satisfactorily naturally represents the best engi- neering. First and most usual is the single-throw system. Fig. 1. It is the least expensive as regards first cost, installation, and main- tenance, and lends itself readily to later additions or modifications. It is used in all cases except where special requirements of the ser- vice or added precautions against failure of supply require modifica- tions, such as in Fig. 2, or the adoption of the double-throw system, 32 Switchboards For Power Stations 1541 Fig. 3. The single-throw bus with tie circuit-breaker, Fig. 2, per- mits operation of a station in separate halves, which is particularly desirable where, for example, the left half of the bus may feed a railway, or other power load, while the right half feeds a lighting load. During the day while the power is large and the lighting load is very small, the tie breaker is closed. When the lighting load comes on, the tie is opened; and, if later in the evening the power load disappears altogether, or its fluctuations are unobjec- Fig. 4 — Smallest Type of Self-Contained Switchboard. Controlling two alternating-current generators with their exciters and two fused feeder circuits with totalizing watthour meter. tionable, the tie breaker may again be closed. The same procedure is possible where the double bus. Fig. 3, is employed. This system, though more complicated, more expensive, and retiuiring more space, gives great flexibility in the handling of load. Moreover, the double bus ordinarily gives adeciuate assurance of continuity of service, and permits of examination and repairs of any circuit- breaker of connections thereto, or to either bus, without discontinu- ing any part of the service. 1541 Switchboards For Poiuer Stations 33 Choice of Apparatus Standard panels containing standard apparatus for various classes of service are listed by the larger electrical manufacturing companies. Three distinct types are commonly provided for as follows: 1 — The small plant where the most inexpensive board is desired, with only sufficient apparatus to fill the absolute requirements for operation of the plant, as in Fig. 4. Fig. 5 — Medium-Size Self-Contained Switchboard for Furnishing Light and Power for Small Town Controls two alternating-current generators, with Tirrill regulator voltage control, two exciters, two power feeders, rectifier circuits for arc lights and alternating-current end of synchronous motor-generator set for supplying direct-current. 2 — For plants of medium capacity larger switchboards are advisable, wherein the circuits are more carefully protected but provided with few meters, as in Figs. 5, 7, 8, and 9. 3 — For the larger plants where the best of circuit-breakers are required and where a full complement of instruments is necessary, as in Fig. 10, The choice of apparatus, and therefore the design of the switch- board, depends on the size and disposition of the output. The grade of intelligence of the attendants may also have considerable 34 Switchboards For Power Stations 1541 SO oz> "UcD ■q o oo CDO chO '"o 0‘S ■g fl g-o w d w* 3 5 j 2 • ■ d 4J -O g (D to y JS y «3 ■S.. s ^ « o flu ©•a u © « c Ce © I 6> © ct «D fl «« 5 « h< CO £e © y S-s •S ° S-- s ^ rt •*-> d ^ o V. •lisil d N ^ y ^ cd;5 S-^ 8 c © 2 'H © o O' 3 CCJ p^Zw^ £?© © ©i2 Si •i3 b © © © 3 o) i'g -g^^^©rt t 22^'0’0 t 3 ©g* Xlw^CCfiM© 4,©gT3333iS'rn -( ® ^ !5 S 2 £ o o *t/2P^[X(000>w iT I I M I I O'O^CNfOr^lOvO 0> M li ■*■> 4-> ■© ti 0-75 g| S 2B^ 3rt©3 (u^M© ■S.sl=S »|2 rt*jbp3g'*-'2© •<-> *0 dj 4-) C3 ^ C3 *7? < 2 E I I i UI I I ^(Nro^iO'Or^OO 1541 Switchboards For Power Stations 35 influence. The magnitude of the output determines to a very consid- erable extent the type of switching devices to be used. The smaller capacity circuit-breakers for 2200, 3300 and 4400-volt service usually have an ultimate breaking capacity of approximately 3000 k.v.a. Fig. 7 — Front and Rear-View Drawings of Switchboard, Shown in Fig. 5 Showing the details of arrangement and location of apparatus. The type of circuit-breaker chosen must be capable of opening the maximum output of the station. For example, if the generating units consist of three 800-k.v.a. machines of the assumed character- istics, the circuit-breakers must have an ultimate breaking capacity of at least 2400 k.v.a. when set for instantaneous tripping. Panel No. 5 P*nel No, 4 Panel No. 3 36 Switchboards For Power Stations 1541 z. 1 7m bsk: €>= mt o ,« 1 J\~< Fig. 8 — Detail Diagram of Connections of Switchboard Shown in Figs. 5 and 7 View from the rear of board. All apparatus is shown as nearly as possible in its relative location. A single line diagram of the board is shown in the lower left-hand corner. 1541 Switchboards For Power Stations 37 The selection of non-automatic oil circuit-breakers and oil switches is not influenced in this way by the capacity of the station, except as they will be called upon under extreme conditions to open the circuit. They should never be required to open the circuit on an overload or even on a normal load, except where absolutely nec- essary to save some more valuable piece of apparatus. Their prin- cipal function is that of main disconnecting switch. They permit quicker and safer closing or opening of the circuits than could be accomplished by the usual lever-type disconnecting switches. Fig. 9 — Rear of a Medium-Sized Board Showing main and small wiring and bus-bars in place. Absence of instrument transformers and other details gives simple and pleasing appearance. They are, therefore, commonly used between generators and bus- bars, where automatic action is undesirable, but where quick manual operation is necessary, as during synchronizing. If it is desired that the non-automatic breakers be suitable for clearing any abnormal condition which is not taken care of by the automatic breakers, it is usually safe to assume that by the time the breaker has been opened by hand the energy is reduced one-half its value at the instant the breaker would have opened had it been automatic instantaneous-trip. 38 Switchboards For Power Stations 1541 If, however, the conditions are such that the maximum current on short-circuit may be sustained longer than the time required to man- ually operate the breaker, the ultimate breaking capacity should be the same for non-automatic as for instantaneous operation. The the principal limiting factor is the amount of current which will flow on short-circuit. The better class of automatic circuit-breakers designed for switchboard mounting should be capable, on instantaneous opera- tion, of opening short circuits on generating systems of capacities Fig. 10 — Large Capacity Switchboard (Feeders Not Shown), Having a Full Complement of Instruments The panels shown control two exciters, an induction motor for one of the exciters, voltage regulator, two 300-ampere and one 600-ampere alternating-current three-phase generators. Each generator panel has three ammeters, power factor meter, alter- nating-current voltmeter, indicating wattmeter and field ammeter. from 5000 to 12500k.v.a. The high-capacity circuit-breakers usually have a separate tank for each pole, with the trip coils, which are actuated from current transformers, mounted outside the tanks. The cheaper class of circuit-breakers usually have series trip coils, that is, coils through which the entire current of the circuit must pass, and a single tank containing all the poles and sometimes the trip coils. Choice of Panel Design Dimensions — The size of the panel and the design of the frame should be in keeping with the apparatus to be mounted thereon 1541 Switchboards For Power Stations 39 A small schedule of apparatus of the cheaper type and of small capacity should have a small panel with light framework to bal- ance the design properly. Obviously a large schedule of heavy-ca- pacity apparatus would be entirely out of place if mounted on small panels with light framework. Two distinct forms of panels appear prominently among the many special panels which have been used ; the 90-inch panel with two or more sections of panel material covering the entire frame from top to floor, Fig. 6 (1 to 16), and the 76-inch panel with one section of panel material 48 inches high with the frame extending uncovered the remainder of the distance to the board 90 Inches High Made from standard 3 by 2 by Vi inch angle-iron with corner angles of the same shape, with two wrought-iron straps inch and with 6-inch channel base weighing 8 pounds per foot. 90 Inches High Made from 1 Vi-inch wrought- iron pipe with one wrought-iron top strap by 1^ inch and with cast- iron foot nuts and panel supports. floor. Fig. 6 (17 to 28). Both forms may be supported by either angle or tubular framework, but the latter form is usually mounted on tubular frame, as the round piping extending below the panel section, with large ornamental foot nuts, presents a more finished appearance. Panel Sections — The determination of the proper number of sections per panel may be influenced by design and arrangement of apparatus, the appearance, strength of the material, and facility in erecting and interchanging. A wide range of selection is presented by the standard lines carried in stock by the manufacturers, and wherever possible some standard size should be chosen. These sizes usually per- 40 Switchboards For Power Stations 1541 mit the best arrangement and are the result of years of experience. Their choice will enable manufacturers to quote their minimum price and delivery. This is even more true when additions or modifications to an existing marble switchboard are to be made, for while the large stocks of polished marble carried by the manufacturers enable them to match an existing board closely, special sizes must be ordered direct f rom Inst. & Svn. Busses Exc. Inst. & Syn,' Busses I.XC. Regulator ^^^Mai^^usBa^ (d) ylnst. & Syn. Busses Bracket Generators Feeders Generators Bracket 1 1 ^ f ^ Fig. 13 — Usual Arrangement of Panels and Bus-Bars System for Switchboard Panels In the arrangement shown at c the station load consists of two parts, lighting and power. A tie switch is provided to permit parallel operation of the two halves of the station when desirable. The feeder panels are placed at the extreme ends of the board to permit addition to feeders without disturbing the rest of the board, lighting feeders being taken out at one end and power feeders at the other. The switchboard and exciters are located in the center of the station with the alternating-current generators symmet- rically arranged on either side. The arrangement shown at d consists of double-throw feeder circuits and single- throw generator circuits. This system may be desirable because of the difficulty of parallel operation where one set of generators differs in characteristics from the other; because of different voltages on the two bus-bars; or because one is alternating and the other direct-current. Dotted lines in the main bus-bar indicate an arrangement for double-throw generator circuits; in the exciter bus-bars indicate that arrangement is made for parallel operation of all exciters; in the instrument and synchroscope bus-bars indicate that arrangement is made for using either set of instruments for the station as desired. the quarries where the selection must be made from unpolished marble of shade and markings, as is being quarried at the time of the order. The usual arrangement for 90-inch panels consists of a 60 to 70-inch upper section with a 30 to 20-inch lower section. Of these the combinations of 65 and 25-inch sections and 62 and 28-inch 1541 Switchboards For Power Stations 41 sections are most used. The usual combinations for the three-sec- tioR panels are, upper 20 inches, middle 45 inches, lower 25 inches; or upper 31 inches, middle 31 inches, lower 28 inches. Black marine finished slate is one of the most serviceable mate- rials for this type of board as well as the cheapest. This has a dull velvety black finish which may easily be kept in good condition. The natural material is usually purple slate. When rubbed with oil this finish will not show oil stains. This feature is of special im- portance whereoilcircuit breakers are mounted directly on the panels for, in spite of all precautions, the oil will usually get on the panels sooner or later. Natural black slate, the best of which comes from Maine, is used without the appli- cation of any artificial finish other than clear oil, and is even more serviceable than the black marine slate, though more expensive. Black marine finish is often applied to marble especially when the voltage of the live parts mounted thereon is too great to permit the use of slate. Thus whole switchboards, or only cer- tain high-voltage sections of slate switchboards, may be made of black marine finished marble. This material is cheaper than the natural polished marble, as no polish is required and the ma- terial is usually that rejected from the natural finished marbles on account of blemishes in marking and coloring. Of the natural finished marble the blue Vermont is the best domestic marble for switchboard work, owing to its good insulat- ing qualities and its uniformity in coloring and marking. White Italian marble, though possessing better mechanical and electrical properties, is usually prohibitive on account of its cost. Its use Fig. 14 — Cost of Three-Phase Switchboards Corresponding to Panel No. 1, Fig. 6* Switchboards for two-phase 2200 volts would cost 2.5 per cent higher than the corre- sponding three-phase boards in capacities from 25 to 800 k.v.a., 4.3 per cent higher in capacities from 1000 to 1200 k.v.a. and 10 per cent higher from 1400 to 2250 k.v.a.; for 6600 volts the two-phase boards will cost 2.25 per cent higher from 75 to 3500 k.v.a. and 10 per cent higher from 4000 to 6000 k.v.a. *When combining panels to make up the cost of a complete board, from this and the succeeding curves, the bus-bars should be calculated separately and a sufficient increase should be made in the cost of the boards if the bus-bar capacity at any panel exceeds the capacity of the panel. 42 Switchboards For Power Stations 1541 is now confined chiefly to those applications in which appearance is a major consideration. All polished marble switchboards for this class of service should have the back and edges, also the sides of all holes, treated with an oil-proof varnish, to prevent oil stains from discoloring the marble. The appearance is considerably improved if a clear varnish is used, as the natural marking of the marble is thus brought out almost as well as when polished. Where Fig. 15 — Cost of Three-Phase Switchboards Corresponding to Panel No. 2, Fig. 6 Switchboards for two-phase 2200 volts would cost 1.75 per cent higher than the corresponding three-phase boards in ca- pacities from 25 to 800 k.v.a., 3.25 per cent higher in capacities from 1000 to 1200 k.v.a. and 10 per cent higher from 1400 to 2250 k.v.a.; for 6600 volts the two-phase boards will cost 1.5 per cent higher from 75 to 3500 k.v.a., 2.8 per cent higher at 4000 k.v.a. and 5 per cent higher from 5000 to 6000 k.v.a. Fig. 16 — Cost of Three-Phase Switchboards Corresponding to Panel No. 3, Fig. 6 Switchboards for two-phase 2200 volts would cost 6.6 per cent lower than the corresponding three-phase boards in capac- ities from 25 to 1200 k.v.a. and 1.6 per cent higher from 1200 to 2250 k.v.a. ; for 6600 volts the two-phase boards will cost 6 per cent lower from 75 to 3500 k.v.a. and 3 per cent higher from 4000 to 6000 k.v.a. The two phase requires but two ammeters and therefore a 16-inch panel may be used, making the total price lower for'two phase up to 1200 k.v.a. at 2200 volts and 3500 k.v.a. at 6600 volts when the change to the 600- ampere switch increases the price to a value higher than that for the correspond- ing three-phase panel. current-carrying parts are mounted directly on the switchboard, slate can seldom be used above 6000 volts, whereas marble may be used for voltages as high as 3300. For the small boards the tubular frame is undoubtedly the best selection. The lower part of these frames which appears between the panel section and the floor does not require any special covering to give a finished appearance. The number of castings, bolts, etc., is small, as these panels usually have but four mounting bolts. 1541 Switchboards For Power Stations 43 and therefore assembly at the factory, shipment, erection and altera- tions or additions are easily accomplished. The frame for multi- section panels, however, presents a different problem. The compari- son between the 2 by 3 by angle frame (Fig. 11) and the \ ]/^- inch tubular frame (Fig. 12) is about as follows: Cost of frame, materials for ship- ment. Cost of packing, painted and assem- bled. Cost of erecting at destination. Mechanical strength and alignment of panels. Tubular frame approximately 25 per cent cheaper. Angle frame approximately 65 per cent cheaper. Angle frame approximately 50 per cent cheaper. Greatly in favor of angle frame. Fig. 17 — Cost of Three-Phase Switchboards Corresponding to Panel No. 8, Fig. 6 Switchboards for two-phase 2200 volts would cost 15 per cent higher than the corresponding three-phase boards in capac- ities from 25 to 1200 k.v.a. and 13 per cent higher from 1400 to 2250 k.v.a.; for 6600 volts the two-phase boards will cost 16 per cent higher from 75 to 3500 k.v.a. and 13 per cent higher from 4000 to 6000 k.v.a. Fig. 18 — Cost of Three-Phase Switchboards Corresponding to Panel No. 9, Fig. 6 The two-phase panels of this type cost approximately 2.3 per cent more than the corresponding three-phase panels. Where angle frames are employed, the panel sections and the two panel uprights form a unit, and may be handled as such in shipping and erecting. As there is no necessity for removing the panel sections from the angle frame before shipment, the panels may be completely wired by the manufacturer before delivery. For the tubular frame, however, one upright is common to two adjacent panels, and to pack the panel as a whole, a temporary upright must be supplied with each panel but one. This renders the packing and erecting at destination so much more difficult, to say 44 Switchboards For Power Stations 1541 nothing of the added expense of the temporary uprights, that the tubular frame switchboards are usually shipped unassembled. Arrangement of Panels A great number of the arrangements of the panels of a switch- board may be made, each possibly with distinctive merits of its own. It is obvious, however, that as there are so many switchboards quite similar in design, as well as in the functions which they perform, there must be some logical arrangement which, in general, meets Fig. 19 — Cost of Three-Phase Switchboards Corresponding to Panel No. 11, Fig. 6 Prices for two-phase panels are approxi- mately 3.6 per cent higher than the corre- sponding three-phase panels. Fig. 20 — Cost of Three-Phase Switchboards Corresponding to Panels Nos. 14, 15 and 16, Fig. 6 almost every requirement. Such an arrangement, as shown in Fig. 13(a), is as follows: Voltage regulator panel (if any) at one end of board followed by exciter panels, generator, totalizing, transformer and feeder panels. Some of the advantages of this arrangement over other possible arrangements are: Ease of adding to the board without materially disturbing the existing panels. By arranging the panels in order of their current capacities, with the heaviest capacity panels at the center of the board, the bus-bar copper is usually reduced to a minimum. The output of the station may be totalized on one set of meters connected to bus-bar transformers, between the generator and the feeder panels. (When the generator panels are separated by feeder panels, totalizing cannot be accomplished without undesirable intricacies in wiring connections.) The alternating-current bus-bars do not cross the exciter panels. The exciter bus-bars are of minimum length. The concentration of various panels of a kind at one part of the board assists the operator materially by reduc- ing the number of steps, and consequently the time required for any switching operation 1541 Sivitchboards For Power Stations 45 The arrangement of panels for each switchboard should, how- ever be given careful consideration. An arrangement may then Te chosen which will suit the local conditions better than the arrange- ment just described (see Fig. 13 (a), (b), (c) and (d)). The deter- mining factors to be considered are: The scheme of main connections, the scheme of operation, the geography of the station apparatus, the arrangement of cables to and from the switchboard, the desirability of totalizing the load, and future additions. Less attention is usually given to the arrangement of cables than their importance warrants. It is not unusual to find arrange- Ann 1 r PANELS Nos. 17, 18 AND 19-nC. 6 Cost in Cents per K. V. A. f ffA Cap! K. V. A. No. 17 No. 18 No. 19 10 20 30 40 50 60 75 100 200 250 300 400 500 600 800 1000 1200 910 455 303.3 227.5 182 151.6 121.3 91 45.5 40 33.3 25 20.5 17.1 12.8 11.5 9.5 1330 665 443.3 332.5 266 221.6 177.3 133 66.5 57.2 47.6 35.6 28.8 24.3 18.2 15.6 13 1490 745 496.6 372.5 298 248.3 198.6 149 , 74.5 63.6 53 39.7 32.2 27.1 20.3 17.2 14.3 1 \ < \ 17 > V k -18 ^.0 \ \ ■19 1 (M? -50- 2 ) ? > K 0 Cents 5 1[ £nj< 9 1 V, , '5 2i <3 . 0 2; S 2 0 i PANELS Nos. 20, 21 AND 22-FIG. 6 K.V.A Cost in Cents per K V A No 20 No 21 No 22 10 20 30 40 50 60 75 100 200 250 300 400 500 600 800 1000 1200 870 435 290 217.5 174 145 116 87 43.5 34.8 29 21.7 17.4 14.5 10.8 8.7 7.2 340 170 113.3 85 68 56.6 45.3 34 17 17.2 14.3 10.7 8.8 7.3 5.5 5.2 4.3 630 . 315 210 157.5 126 105 84 63 31.5 At^(\ 1 40 \ “250 - ^ 2l 200 \ \ "lOO 2^-3 [T^ 5 1 WT: |nls K \( r5 2 A >0^ /b Fig. 21 — Cost of Three-Phase Switchboards Corresponding to Panels Nos. 17, 18 and 19, Fig. 6 Prices for two-phase 2200-volt board of the type corresponding to panel 17 will be 0.5 per cent higher than the correspond- ing three-phase panel from 10 to 200 k.v.a. and 6 per cent higher from 200 to 1200 k.v.a.; for panel 18, 0.5 per cent higher from 10 to 800 k.v.a. and approximately the same price above 1000 k.v.a.; for panel 19 approximate- ly 0.5 per cent higher throughout. The prices for two-phase and three-phase pan- els of these types are almost identical owing to the fact that a narrower panel and but two ammeters for two-phase offset the four-pole breaker and additional wiring. Fig. 22 — Cost of Three-Phase Switchboard Corresponding to Panels Nos. 20, 21 and 22, Fig. 6 Prices for a two-phase board of the type corresponding to panel 20, Fig. 6, are approx- imately 8 per cent higher than for the corresponding three-phase panel; for panel 21, 6 per cent higher from 10 to 200 k.v.a., and 16 per cent higher from 250 to 1200 k.v.a.; and for panel 22, 11 per cent higher. ments which save copper in the bus-bars at the expense of increase in the cost of cable. Later additions are often made at excessive cost and great inconvenience to the operation of the station. Blank panels properly located during the initial installation usually save many times their cost. A carefully prearranged scheme of inter- 46 Switchboards For Power Stations 1541 changing panels may, however, permit the making of all necessary additions. For example, the bus-bars, instrument transformer supports and all openings in the floor may be arranged so that they will suitably accommodate future additions. Arrangement of Apparatus The usual arrangement of apparatus on individual panels as recommended by best practice is shown in Fig. 6. Some operators prefer arrangements which differ, more or less, from those illus- trated, and in some cases the conditions may warrant radical depar- tures, but if the following requirements are complied with it will usually be seen that the arrangements illustrated are obtained : Fig. 23 Fig. 24 Fig. 23 — Single Generator Rheostat Supported from Back of Panel by a Single Bracket Fig. 24 — Generator and Exciter Rheostat Mounted in Combination and Supported from Single Bracket Fig. 25 — Combination Mounting of Handwheels with Generator Rheostat Mounted Near Either Top or Bottom of Board; Exciter Rheostat on Single Bracket 1 — Indicating instruments should be mounted at or a little above the height of the eyes. 2 — Meters of a kind (for example, ammeters) should be symmetrically grouped on the panel so that phase distinctions are apparent. 3 — Meters of a kind should be in alignment with each other on the various , panels, for convenience, appearance and symmetry of wiring. 4 — Voltmeter receptacles and similar plugging devices should be located as near the instruments as possible to simplify and decrease amount of small wiring. 5 — Rheostats, unless very small, should be sprocket operated, the face plates and resistance mounted as a unit and located in some con- venient place where the contacts may readily be inspected and where the heat from the resistance will do no harm. The handwheels should be located near the center of the panel at such a height that the operator may readily watch his instruments while adjusting the rheostat and can have one hand free to operate the voltmeter receptacle, field switch or main switch. 1541 Switchboards For Power Stations 47 6 — The main switches or circuit-breakers should be located at a height most convenient for ease in operation. They must not be so close to the edge of the panel section as to interfere with the frame work or to give insufficient distance to the adjacent apparatus, or so near the floor as to prevent free removal of the tanks for inspection. 7 — Watthour meters or relays may be mounted on the subsections or at the rear of the board, as they require only occasional attention. 8 — High-tension bus-bars should be mounted near the top of the board to avoid accidental contact, thus obviating the necessity of insulating them to prevent injury to attendants. This arrangement also per- mits free access to the rear of the board. 9 — Voltage and current transformers may be mounted at the rear of the board on suitable supports, but usually at the expense of accessibility to the instrument wiring and auxiliaries mounted on the back of the panel, and of the general appearance of the installation. It is recom- mended that they be placed apart from the board wherever possible, (see Fig. 9); beneath the floor if the leads go down, or on the wall where they go up. 10 — Such instruments as graphic recording meters, static ground detectors and voltage regulators should not be placed on swinging brackets or swinging panels. Costs The curves with tables, Figs. 14 to 22 inclusive, showing the cost in cents per kilovoltampere capacity, will indicate the relative costs of the various panel arrangements and of the comparative cost of 2200 and 6600-volt panels. The figures given include all wiring details, and bus-bars of the rated capacity of the panels. The tables permit a more accurate interpretation of the curves and also indicate the values beyond those shown by the curves. The irregularities and breaks in the curves are occasioned by the fact that two sizes of oil switch are involved, namely the 300 and 600-ampere capacities. The change in capacity for this rating comes between 1200 and 1400 kilowatts for 2200-volt panels, and between 3000 and 4000-kilowatt capacity for 6600 volts. As shown by the curves the prices of the generator panels are usually the same, regardless of k.v.a. capacity, up to 500 or 800 k.v.a. Above these capacities they increase by steps owing to additional cost of current transformers, panel wiring etc., until the sudden change to the higher capacity switches causes a break in the curve. The two-phase panels usually exceed the three- phase panels in cost by the cost of the extra circuit-breaker pole and its wiring, but this is not true where three ammeters are used for three phases and two for two phases, as the fewer meters and the narrower panel may make the two-phase cheaper than the three- phase panel. 48 Switchboards For Power Stations 1541 Rear of Board The design of the rear of a switchboard is a good indication of its real worth as an engineering production. Even more care is necessary than for the front, as it is here that switchboard troubles most usually occur, and the chance of their occurrence is multi- plied if a careless or inconsistent design is adopted. It is a com- paratively simple matter to produce a well-arranged, well-appearing front, but the rear of the board with its many details, forming a combination of high and low-voltage conductors, moving mechanical parts, instrument and control wiring, oil circuit-breakers, rheostats, etc., presents a problem which requires originality and systematic design on the part of the engineer and a skilled and patient draughts- Fig. 26 Fig. 27 Fig. 28 Fig. 26 — Same as Fig. 25 Excej^t Generator Rheostat is Mounted on the Floor or Supported From the Ceiling Fig. 27 — Remote Control Wall Mounting of Large Generator Rheostat Showing three Good Methods of Arranging the Control Fig. 28 — Handwheel of Generator and Exciter Rheostat Mounted in Combination; Both Rheostats Remote-Controlled man. This is probably more true of the self-contained switchboard than of any other, as the greater part if not all, of the auxiliary apparatus is mounted upon or supported from the rear of the board. This auxiliary apparatus consists chiefly of bus-bars, instrument wiring, instrument transformers, fuse blocks and fuses, main inter- connections with their supports, instrument and discharge resistances and rheostats, but very often it is necessary that space be found for disconnecting switches, fuses for main circuits, wattmeters and relays. This is obviously bad engineering and should be avoided by finding room for much of the high-voltage apparatus, such as instrument transformers, disconnecting switches and fuses away from the board itself (Fig. 9). This treatment permits an accessible, open arrange- 1541 Switchboards For Power Stations 49 mcnt of the main and control wiring and other apparatus which should naturally be mounted on the back of the panels. Rheostats, when small, are best located at the rear of the board, preferably supported on brackets which will not materially de- crease the space required for instrument wiring and other details (Fig. 23). When individual exciters are used with the generators their rheostats may be mounted in combination, the handwheels being eccentric on the front of the panel, the main rheostat being controlled by means of a hollow shaft which contains the shaft of the exciter rheostat (Fig. 24). Where the size of the rheostats precludes the combination mounting, the concentric handwheels may still be retained by mak- Fig. 29 — Suggested Arrangement for Large Remote-Controlled Rheostats ing the main rheostat sprocket operated, and locating it near the top or bottom of the panel (Fig. 25). The larger capacity rheo- stats, whose resistance must be made up of cast-iron grids, should be mounted entirely independent of the board (Fig. 26). It is not good practice to mount the face-plate at the board and the resist- ance apart from it because of the great number of cables required to connect one to the other, a 48-step face-plate, for example, re- quiring 49 leads. The better method is to mount the face plate as indicated in Figs. 28 and 29. Cables to and from the switchboard should be supported in such a manner that their weight will not be suspended from a soldered joint or the terminal of a circuit-breaker. Cables should not be used 50 Switchboards For Power Stations 1541 as connections for switchboard apparatus where bends are necessi- tated, as they will not keep their form unless carefully supported or enclosed in a stiff covering. Connections are preferably made of flame-proof solid wire, well insulated against accidental contact. If the connection is of too large capacity to be made with one 0000 wire, and it is inadvisable to use two or more, bare copper rods, tubes or straps should be used. This should be well insulated after erection with varnished cambric tape or its equivalent, to protect against accidental contact, and it is advisable to flame-proof all such insula- tion with asbestos tape or some equivalent. To give it permanency the asbestos tape should be treated with a binding solution such as silicate of soda. Practically all switch-board-mounted circuit- breakers are now designed so that their terminals may be conven- iently insulated by taping or by removable tubes. When tubes are used the connection to the circuit-breaker must rise vertically the height of this tube to permit access to the terminals. All connections, both main and auxiliary, should, when at all possible, be run vertically and horizontally with right-angle bends made to a sufficient radius, so that the conductor will not be in- jured. The same suggestion applies to any straps, brackets, braces or other members of the switchboard construction, for the appear- ance of the board is very greatly bettered thereby. This rule is of further advantage in producing a uniform spacing throughout if properly executed, whereas any other method will result in many of the conductors being much closer together at some places than at others. This results either in the loss of the factor of safety in insulating distance, or an increase in the depth of the entire arrange- ment. 1541 Switchboards For Power Stations 51 Fig. 1 — Switchboard of Medium Size For controlling two exciters, two generators, and one feeder as shown in Fig. 3. An alternating-current ammeter, voltmeter, indicating wattmeter, power factor meter, and field ammeter are used for each generator with watthour meter mounted on the rear of the panel. The motor panel accommodates the voltage regulator as well as the circuit- breaker handle and ammeter for the motor. The exciters have individual ammeters and a common voltmeter, while the feeder is provided with a graphic indicating watt- meter and a polyphase watthour meter. that their use has become very frequent. In many cases they are given preference over the self-contained or the electrically operated designs, owing either to the many desirable features secured with very little increase in cost, or to the fact that for many installations REMOTE MECHANICALLY-CONTROLLED SWITCHBOARDS By C. H. SANDERSON The many advantages to be gained from the use of the remote mechanically-controlled type of switching apparatus have been so readily recognized by those having switchboard problems to solve 52 Switchboards For Power Stations 1541 the remote mechanical control provides the same desirable operating features as may be obtained by the use of electrically-operated switching apparatus with a great decrease in cost. Fig. 2 — Rear View of Switchboard Shown in Fig. 1 The watthour meters for the generator, motor, and feeder circuits are mounted on short brackets at the top of the board above the direct-current field bus. The shunts of the exciter ammeter, at left of board, are mounted on a slate base. The equalizer rheostat is mounted on the sub-paneJ. The next panel contains the voltage regulator resistances, with condensers and brackets for circuit-breaker relays mounted beneath. The two generator panels contain the field-ammeter shunt, sprockets and idlers for the rheostat, controller for engine governor motor, and ammeter receptacles. Remote mechanical control of switching apparatus was perhaps first used in connection with high-voltage carbon circuit-breakers. Before the advent of the oil circuit-breaker, alternating current circuits above 600 volts were commonly opened with carbon breakers which were usually separated by large fireproof barriers. They were mounted at the top of very high panels so as to protect the attendants against accidental contact. Remote mechanical control was thus necessitated, and the convenience and safety secured by its 1541 Switchboards For Power Stations 53 use soon led to the removal of dangerous or bulky apparatus from the switchboard panels. The first oil-circuit-breakers were of such design and capacity as to be easily adapted to switchboard mounting However, the demand for larger generating units and higher voltages soon necessitated circuit-breakers of a size and weight suitable only for separate mounting. So great has been the demand for hand-oper- ated remote-controlled switching apparatus that practically all switching apparatus, regardless of size or capacity, may now be obtained suitably arranged for remote man- ual operation. Many of the plants of smaller ca- pacity which could read- ily have used panel- mounted apparatus have felt justified in incurring the small extra expense necessary to provide the remote mechanically- controlled equipment. Many of the large central stations and transmission companies, while using electrically operated equipments in their main gener- ating and transforming stations, have adopted remote control for the same class of apparatus in their sub-stations. Advantages The advantages gained by the use of remote mechanical control over that of the self-contained boards may be summarized briefly as follows: 1 — All high voltages are removed from the panels, thus per- mitting ready inspection of the instrument and control wiring, eliminating danger of injury to attendants from contact with live parts, permitting the location of the board to much better advan- tage as regards the remainder of the installation because less space and less protection are required. 2 — Panels are not subject to the mechanical strains due to automatic operation or to the dead weight of the apparatus. Sh. Fid. Fig. 3 — Diagram of Connections for Switchboard Shown in Figs. 1 and 2 54 Switchboards For Power Stations 1541 3 — In case of marble panels their appearance is not marred by stains from creeping oil. 4 — Violent explosions which sometimes occur upon the opening of heavy currents or the possible failure of a circuit-breaker will not injure the panels and, if the circuit-breakers are sufficiently spaced or are enclosed in fireproof cells, adjacent circuit-breakers will not be affected. 5 — The panels may be much narrower, the reduced cost thereof offsetting, to a considerable extent, the additional cost of the remote- control feature. Moreover, the decrease in total length of the board may result in a very material saving in cost. 6 — A more compact arrangement of the apparatus is ofgreat as- sistance to the operator, approaching as it does more nearly to the com- pact and efficient arrangements obtained by means of control desks. 7 — Much shorter main connections are made possible, and high voltages kept away from certain floors, or certain rooms by locating the remote-control structure properly. Meters Fig. 4 — Large Remote-Control Switchboard For light and power distribution, controlling apparatus as shown in Fig. 6. are'provided with black-faced dials with white lettering. 1541 Switchboards For Power Stations 55 8 — Where a wall is used for supporting the apparatus, the cost of the complete outfit may be reduced to very near that of the self-contained type of board, and, in some cases of very heavy capacities at low voltages, may be less in cost. Moreover, accessible arrangements of apparatus with ample spacings may easily be obtained. 9 — Where a steel or masonry structure is used, access may be had to either side of the structure and an arrangement of this Fig. 5 — Rear View of Switchboard Shown in Fig. 4 The calibrating receptacles may be seen near the bottom of the alternating-current panels, with the relays just above them. On the exciter panels are shown the double exciter bus, direct-current watthour meter and equalizing rheostat. kind will satisfactorily accommodate the maximum amount of appara- tus ordinarily used for either single or double-throw arrangements. In comparison with the electrically operated board, the remote mechanically-operated board usually occupies from 5 to 50 per cent more space although the circuit-breakers and bus-bars for a given capacity will be practically identical. The size of the board in either case depends primarily on the number of instruments employed for each circuit, as they require more width than the control handles of 56 Switchboards For Power Stations 1541 the circuit-breakers. The boards themselves may be identical throughout as to equipment except for the method of control of the circuit-breakers and usual attendant difference in method of auto- matic relay tripping of the circuit-breakers, the electrically-operated boards using direct current, and the remote mechanical control alter- nating current for this purpose. Application The remote mechanically-controlled switchboard is limited in capacity by physical rather than electrical characteristics. As nearly all high-capacity circuit-breakers may be arranged for remote me- chanical control as well as electrical operation, the problem becomes one of mechanical arrangement in which it is usually very easy to meet the electrical requirements. The principal rules to be observed as regards the mechanical limitations may be stated briefly as follows : Fig. 6 — Single-Line Diagram of Connections of Switchboard Shown in Figs. 4 and 5 A circuit-breaker should close readily with the ordinary effort exerted by the average man. It is impracticable to operate a circuit- breaker satisfactorily when the total length of operating rods exceeds approximately 50 feet. In general, a horizontal distance much in excess of 35 feet or a vertical distance of 20 feet should not be exceed- ed with standard commercial apparatus. This distance may prove too great for satisfactory operation, especially for the larger sizes of breakers, if more than two bell-cranks must be used or if the direc- tion of motion must be changed, as in clearing columns or other obstructions. The inertia of the mechanism should not be sufficient to materially affect the time or power required to close the breaker. The mechanism should be so arranged, if possible, that rods are in tension when the breaker is being closed. When the mechanism operates vertically, as when controlling circuit-breakers on floors above or below the switchboard, the mech- 1541 Switchboards For Power Stations 57 anism may be counterweighted to take the weight of the vertical rod off the operating handle; but, as the inertia of the mechanism is thereby increased, the application of counterweights is limited. In view of these considerations it is recommended that this type of switchboard be confined to the use of circuit-breakers of 3000 am- peres capacity or less and of 35000 volts or less, and to stations whose capacity does not exceed 25000 k.v.a., three-phase. Fig. 7 — Lighting and Power Alternating and Direct-Current Switchboard for Small City This is an unusually compact form of board for the apparatus it controls, as shown in the diagram, Fig. 9. Types The multi-section panel 90 inches high is almost universally used for this class of board. The installation which requires the use of remote control apparatus is of such capacity that the smaller type of board would not be in keeping with the remainder of the equip- ment. For individual circuits or very small substations, or when 58 Switchboards For Power Stations 1541 associated with smaller direct-current boards, however, the smaller type of panel may be employed economically and to good advantage. Figures 1, 2 and 3 illustrate the type of board often used for a hydro-electric plant of medium size where all the power generated is taken over one feeder to the center of distribution. The exciters which are operated in connection with a voltage regulator, are con- trolled from a double-exciter panel containing the ammeters, a Fig. 8 — Rear View of Switchboard Shown in Fig. 7 The small amount of space occupied and the accessibility of all parts are clearly shown. common voltmeter, main and equalizing rheostats, and main switches. The second panel contains the handles for the automatic protective circuit-breaker and the starting circuit-breaker, and the ammeter for the exciter motor, as well as the regulator. The two generator panels are each equipped with ammeter, voltmeter, power factor meter, indicating wattmeter and held ammeter, and the usual switches, circuit-breaker handle, plugs and receptacle with the addi- IPaoel No. ,U/ Pan 1541 Switchboards For Power Stations 59 9 — Complete Diagram of Connections for Switchboard Shown in Figs. 7 and 8 Two synchronous motors are controlled from one panel No. 6, 24 inches wide, with sufficient space reserved for a third. Two generators are con- trolled from panel No. 10, 16 inches wide, with panel No. 9 reserved for two* future generators. Each of the 16-inch feeder panels controls two feeders. The direct-current, three-wire generators are protected by series relays connected directly to the armature circuits. 60 Switchboards For Power Stations 1541 tion of a governor speed controller. The feeder is provided with a graphic wattmeter and an automatic circuit-breaker with relays, the latter usually inverse or definite time limit, but often reverse power where the station feeds into a system of power stations. Boards for large industrial, or light and power plants are illustrated in Figs. 4, 5 and 6. This particular equipment is mainly double throw, as illustrated in Fig. 6. The meters are all provided with black dials with white scales and lettering, which are generally considered much easier to read than the white dial. The bracket instruments, which are mounted on a swinging panel, consist of two voltmeters, a synchroscope, power factor meter and frequency meter. The generator panels are each equipped with two ammeters, indicat- Fig. 10 — Remote-Control Switchboard Instrument buses taped in one group. Auxiliary knife switches for instrument leads mounted above and connected to oil circuit-breaker handles. Conduits for instru- ment wires taken through channel base of switchboard. Extreme depth of board over all, 18 inches. ing wattmeter, voltmeter, field ammeter, watthour meter; while the feeder panels each have one ammeter with receptacles for each phase, and a watthour meter. Two good methods of mounting watthour meters are illustrated in Figs. 2 and 4, the former on brackets at the rear of the board near the top and the latter on the front on sub- sections. Fig. 5 shows the usual method of mounting relays and calibrating receptacles at the rear of the board. The switchboard illustrated in Figs. 7, 8 and 9 is a good example of the compact, yet efficient, arrangement which this class of board affords. Sub-section mounting of relays on the front of the board is shown in Fig. 7. 1541 Switchboards For Poiver Stations 61 62 Switchboards For Power Stations 1541 Fig. 12 — Control Desk and Instrument Panels Equipped for Remote Mechanical Control are lost in a properly designed desk for remote mechanical con- trol and, as the cost does not greatly exceed that of the panel type, there is no reason why it should not be chosen for stations requiring a large control equipment. The control desk (Figs 11 and 12), though not yet used to any considerable extent when mechanical control is employed, is very popular for controlling electrically-operated equipments because of its many desirable features. Few of these features 1541 Switchboards For Power Stations 63 IV REMOTE MECHANICALLY - CONTROLLED SWITCHBOARDS— Continued By C. H. ANDERSON Choice of Arrangement for Circuit-Breaker Structure The choice of the proper form of structure for the apparatus which is to be remote controlled and the satisfactory arrangement of the apparatus thereon presents a more difficult problem than does the design and arrangement of the panels themselves. The reason lies in the many practical forms of structure, and the large number of arrangements of the apparatus which may be made upon each of the various forms. For example, there are, first, the single-throw and double-throw systems. Under each of these the following arrange- ments are commonly employed: ' Fig. 1 — Wall Mounting Arrangement for Un- Fig. 2 — Separate Mounting Arrange- enclosed Circuit- Breakers and Bus-Bars ment With Brace to Wall 1 — Wall Mounting — -All apparatus and bus-bars either mounted directly on or supported from a wall of the building (Fig. 1). 2 — Framework Mounting — All apparatus and bus-bars mounted on a frame- work of iron pipe or structural steel shapes, or a combination of the two (Figs. 2 and 3). 3— Combination Wall and Framework Mounting — As illustrated by Figs. 4, 5 and 6. 4 — Concrete or Masonry Structure Mounting — All apparatus and bus-bars mounted in cells or compartments, as shown in Figs. 7, 8 and 10. 5 — Combination Concrete and Structural Mounting — Circuit-Breakers in concrete cells, remaining apparatus on iron framework, Fig. 9. 64 Switchboards For Power Stations 1541 Many modifications of these arrangements are made as the conditions and surroundings warrant. Cells of asbestos lumber, slate, soapstone, moulded concrete or other suitable material are frequently used to enclose all or a part of the circuit-breaker where schemes 1 or 2 are employed. The remote-control structure may be divided into two parts; the circuit-breakers for example, being mounted on the switchboard room floor with the bus-bars and auxiliary apparatus mounted in the room beneath. The following apparatus must usually be considered in choos- ing a satisfactory arrangement; Circuit-breakers, bus-bars and connections, rheostats, instrument transformers, fuses for potential Fig. 3 — A Motor-Generator Substation Switching Equipment for 1,500-volt Direct-Current Railway Showing arrangement of starting and main alternating-current bus-bars (Piedmont Traction Co.), and assembly of all disconnecting switches and instrument transformers on the tubular framework. The control for rheostats, as well as circuit-breakers, is taken beneath a section of removable flooring. The direct-current circuit-breakers are also remote controlled from the middle section of the board, the switches being mounted on separate braces at the rear, near the top of the board. transformer primaries and for main wiring when employed, and dis- connecting switches. Before a proper choice can be made, a con- plete diagram, including all main wiring and all of the above appara- tus, should be carefully made, according to the system of connections which has been adopted for the installation under consideration. 1541 Switchboards For Power Stations 65 From this wiring diagram should be selected the circuit which pre- sents the most complications; that is, the greatest number of dis- connecting switches, instrument transformers, etc., and, with the various practical forms of structure in mind, an arrangement should be worked out for this unit of the structure. If the remaining circuits have the same, or a less number of members in the same relative location in the circuit as regards the oil circuit-breakers, the problem is solved and the remainder of the work is simply duplication. If the members in some circuits appear in other locations than those in the circuit chosen, each differing unit must be worked out indi- vidually , with a view, however, of forming them into a sym- metrical and uniformstructure. The choice of arrangement depends upon the capacity of the station, the cost the available space, the voltage, the type of circuit-breaker chosen, and the current capac- ity of individual circuits. Discussion The capacity of the station, that is, the entire amount of energy which can be concen- trated on the bus-bars, decides the capacity of circuit-breaker to be used and the capacity and design of the bus-bars, connections, and auxiliary ap- paratus. The comparative costs of the various arrange- ments are indicated approxi- mately in Table I, the costs given covering in each case all frame- work, (two uprights) or concrete, and mountings for one three-pole circuit-breaker with instrument transformers, etc., and with remote- control mechanism; in other words, all material which must be added to the self-contained type of board to make it remote controlled. It should be remembered that wall arrangements such as shown in Fig. 1, may be more costly than the separate arrangement shown in Fig. 2, if large windows, which must be bridged by steel work, oc- cur back of the board. Concrete or masonry structures may add con- Fig. 4 — Combination Wall and Framework Mounted Structure For heavy current capacity at low voltage. Similar to arrangement shown in Fig. 6. In- expensive arrangement of control mechanism. Space back of board entirely free from main current-carrying parts. 66 Switchboards For Power Stations 1541 siderable to the cost of floor construction and support on account of their great weight. The wall-mounting arrangements, shown ip Figs. 1 and 8, occupy the least space but have the disadvantage of Table I. Wall mounting (Fig. 1) including I-beam supports for remote- control mechanism $ 8.00 Separate mounting (Fig. 2) including I-beam supports for re- mote-control mechanism 13.00 Combination wall and separate mounting (Fig. 4), including slate false flooring over mechanism 10.50 Combination pipe and concrete structure (Fig. 9). $35.00 to 40.00 Wall-supported concrete structure (Fig. 8) 75.00 to 100.00 Separate concrete structure (Fig. 7) 75.00 to 100.00 Fig. 5 — Large Remote-Controlled Switchboard With apparatus arranged similar to Fig. 4. Rheostats mounted in view of operator above the board. (Marathon Paper Company.) giving accessibility from one side only. For this reason and because of the great increase in available space for mounting various members of the assembly, the separate-mounted structures are preferred where space can be found. Fig. 4 shows approximately the minimum space which is required for the average structure, while more generous space is provided in Fdg. 2. All high-tension connections and circuit- breakers in Fig. 4 are on that side of the supporting framework away from the switchboard, and the remote-control mechanism is of mini- 1541 Switchboards For Power Stations 67 mum length and weight. Moreover, if desired, a metal screen may be placed along the structural uprights, entirely separating the low- tension wiring and- details on the back of the board from the high- tension apparatus, thus insuring the safety of attendants when work- ing at the back of the switchboard. The voltage of the system determines the spacing of the vari- ous members of the arrangement and influences the size and type of the circuit-breaker chosen. Moreover, it has certain influence on the arrangement in that concrete or masonry structures are not recommended for voltages above 13200 volts. This recommenda- Fig. 6— End View of Remote-Controlled Switchboard Shown in Fig. 5 False flooring over control mechanism not shown. enclosed in cells if desired, as shown in Fig. 1. By the latter is meant those circuit-breakers assembled from unit poles, each pole being de- signed to occupy a separate cell, as shown in Fig. 10. The current capacity of the individual circuits determines the size of the circuit-breaker, and the nature of th^ connections between circuit-breaker and bus-bars; that is, whether solid wire, copper rod, copper tubing, or copper straps must be used. Moreover, the current capacity determines the type of current transformers. Those shown in Figs. 1 and 2 are for small current capacity and require tion is due to the fact that for higher volt- a g e s, concrete or masonry structures must be considered as “dead ground” and therefore, since the tendency toward leakage and corona increases as the volt- age increases, safe spacing distances would necessitate a very large and expen- sive structure. There are two kinds of circuit-breakers as regards their mount- ing : those designed for wall or pipe-frame mounting and those forcellmounting. Any of the former may be 68 Switchboards For Power Stations 1541 special mounting, whereas those shown in Fig. 4, for large-current capacity, are designed to slip over the laminated strap connections and do not require special support. The Remote-Control Mechanism The control mechanism which is used to the practical exclu- sion of all others for switches and circuit-breakers consists of a Fig. 7 — Concrete or Masonry-Enclosed Separate-Mounting Structure Typical arrangement of apparatus and bus-bars. 13200-volt apparatus shown. Self-supporting and accessible from both sides. May be entirely enclosed by use of cell doors. Fig. 8 — Wall Mounting Concrete or Masonry Enclosed Structure 13200-volt apparatus shown. Requires but little space. Accessible from one side only. Provides space for but one set of disconnecting switches. Fig. 9 — Combination Concrete or Masonry and Pipe Framework Structure; Self-Supporting Comparatively inexpensive construction, is of less width than arrangements of Figs. 7 and 8, but live parts are unprotected. 6600-volt apparatus shown. series of levers and rods. The direction of the operating force is always linear, changes in direction being made by means of short levers rotating on a fixed fulcrum commonly known as “bell cranks” (Figs. 1 1 and 12). This type of mechanism lends itself readily to the 1541 Switchboards For Power Stations 69 application of automatic action, especially where the latch and trip coils are located at the operating handle. The connecting rods (Fig. 11 and 12) are commonly made of three-fourths inch gas pipe, as it is cheap and usually easy to obtain, and is naturally well suited for the purpose. Wooden rods are sometimes used because of their light weight, and in some cases, such as for field switches or disconnecting switches, on account of their insulating properties. Mechanisms for automatic circuit-breakers are of two kinds; those in which the mechanism is stationary during automatic trip- ping of the circuit-breaker, in which case the circuit-breaker is said to trip free from the mech- anism, (Fig. 12), and those in which the mechanism returns to the open position (Fig. 11) at the time of opening of the cir- cuit. The latch and trip coils may be mounted at the circuit- breaker for both kinds, but it is most usual with the latter kind to mount them at the operating handle. The arrangement of mounting the trip coils and latch at the control handle with the control mechanism and breaker both tripping free from the handle is the most commonly used. The trip coils or relays if used, are usually actuated by the same current transformers which operate the ammeter, and this arrangement permits all sec- ondary wiring from the current transformers to be made at the switchboard. Moreover, as the auxiliary lever (Fig. 11) indicates the open or closed position of the circuit-breaker, the operator does not require a signal device at the switchboard for this pur- pose. Where the distance from the switchboard to the circuit- breaker is considerable, however, it is advisable to place the trip coils, latch, and relays, if used, at the circuit-breaker so that the latter will trip free from the heavy mechanism. In this case an indicating device at the switchboard, such as a lamp or mechani- Fig. 10 — Oil Circuit-Breaker Structure Corresponding to Fig. 8 Showing front view of wall-mounting structure. Two complete circuit-breaker units shown. (Used by Development & Funding Company.) 70 Switchboards For Power Stations 1541 cal signal,^ is desirable even though the instruments may indicate, to a certain extent, the condition of the circuit. A long heavy mech- anism will considerably increase the inertia of the moving element Fig. 11 — Remote-Control Mechanism With Latch and Trip Coils at the Handle Fig. 12 — Remote-Control Mechanism With Latch and Trip Coils at the Circuit-Breaker The mechanism does not move when breaker opens automatically. Automatic action of the breaker is indicated at the board by some form of signal device. Mechanism moves when oil circuit-breaker opens, the auxiliary handle lever tripping free from the handle while the main handle lever remains in lower position. Mechanism shown just after tripping. and consequently slow down the action of the circuit-breaker. If, therefore, this form of mechanism must be used, an accelerating device such as a spring, combined with a dashpot to absorb the shock of opening, should be applied to regain the inherent speed of the breaker. 1541 Switchboards For Power Stations 71 Most mechanisms have considerable flexibility, however, owing to the manner in which they are supported, and therefore the spring need not be used except on short rigid runs of mechanisms and where the connection is made direct to the circuit-breaker without the use of bell cranks. Fig. 13 — Substation Arrangement of Switchboard Including remote-control high-tension breaker, bus-bars, transformers, lightning arresters, choke coils and disconnecting switches. 72 Switchboards For Power Stations 1541 V REMOTE MECHANICALLY - CONTROLLED SWITCHBOARDS— Continued By C. H. SANDERSON \ Structure Arrangements The various possible arrangements of remote-controlled switch- ing equipments may be divided into two classes as influenced by the system of connections employed, namely, single throw and double throw. Either of these classes may be arranged for wall mounting and mayemploytheopen, semi-enclosed, or entirely-enclosedstructure. Aside from the inevitable circuit-breakers, bus-bars and connections, any arrangement under consideration may be influenced materially by the presence of disconnecting switches, fuses, and instrument transformers in various parts of the circuit. There is usually much to be gained, not only in economy of cost but also in appearance, simplicity and ease of operation, by selecting just the right arrange- ment for the conditions obtaining. As an assistance, therefore, to the proper selection of apparatus and layout, the accompanying illustra- tions are presented. While the usual arrangements are fairly covered it is quite possible that the best arrangements for a particular schedule of apparatus may only be secured by combining certain desirable features from two or more of the arrangements illustrated. As a further assistance in deciding upon the best arrangement, it may be said that small stations of 3000 k.v.a. or thereabouts are hardly justified in employing any other than the open arrange- ment, unless local rules demand that the apparatus be enclosed. Even in this case metal grill work would be much more in keeping and much less expensive than cement structures. When the circuit- breakers employed are of the type having one supporting frame for all poles, and it is considered advisable, because of the frequent heavy overloads and short-circuits, to enclose the circuit-breakers in cells, the semi-enclosed type is usually chosen. If, under the same con- ditions, the current capacity is large, or if these circuit breakers are of cell-mounting type, it is usually preferable to employ the com- pletely-enclosed arrangement. There is little choice between the horizontal bus-bar and the vertical bus-bar arrangements from an electrical viewpoint, as per- 1541 Switchboards For Power Stations 73 Fig. 37 — 2200 Volts Two-Phase Bus-Bar Structure, for Ring Bus as illustrated in cross-section in Fig. 35 cuits at some other part of the system or from something falling against or upon the bus-bars or connections. The entirely-en- closed structure is the only real insurance against excessive in- jury to the equipment in case of arcing grounds. In the design of the enclosed structure, it is, however, of great importance, es- pecially when the higher voltages (11000, 13200, etc.) common to structural mounting are employed, that openings at different parts of the structure, which might create a path for drafts, be avoided. For the lower voltages, especially 2200 volts and below. fectly satisfactory designs may be obtained from either. From a mechanical viewpoint the vertical bus-bar requires greater height and less width but practically the same amount of supporting framework and the same length of connections. It is obvious that with the open-mounted vertical bus-bars, the danger of an arc starting at some point on one of the lower bus-bars and short- circuiting the upper ones is greater than with the open mounted horizontal bus-bars. An arc may start at any point where the insulation to ground fails, where current-carrying parts of oppo- site phase or different voltage are too close together, due to faulty erection, to accidental displacement of the members, by short-cir- 74 Switchboards For Power Stations 1541 the copper connections are usually very heavy and of large, usually rectangular, cross-section. It is difficult to take such a connection through a wall without considerable expense and local heating of the conductor, except by means of an opening large enough to give sufficient insulation of air around the conductor. While the enclosed structure has many advantages for in- stallations of medium voltage and current capacity, its use cannot be justified for 440 and 220-volt installations. The danger from arcing is here negligible and the matter of thorough ventilation for bus-bar and connections is of prime importance. This may be appreciated from the fact that the heating on 60-cycle bus-bars of heavy capacity is approximately twice that on direct current. When choosing an arrangement for a double-throw system, it is highly recommended, especially for stations of medium or large capacity, say 3000 k.v.a. and above, that the two halves of the equipment be widely separated by a fireproof wall if possible. This arrangement both minimizes the possibility of shut-down and permits safe inspection, or work to be done on the idle equipment. When there are a considerable number of circuits to be con- trolled, necessitating the use of many circuit-breakers, it is neces- sary to consider carefully the location of the switching equipment in regard to the switchboard panels. The angle at which the mechan- ism leaves the panel is of no consequence except as it causes interfer- ence of the bell cranks and their supports immediately connecting to the control handle. The length of the mechanism and the con- sequent weight, however, have much to do with satisfactory opera- tion. When two^or more circuit-breakers are controlled from one panel of a large board it may be necessary even to form the structure in a double row, back to back, somewhat as shown in Figs. 4 and 5, with the bus-bars in the shape of a U, in order to keep the mechanism more nearly at right angles with the board, thus avoiding interfer- ence of the bell cranks. Costs Table I gives approximate total costs, exclusive of installation, of various panels with complete remote-control arrangement based on the panel schedules and arrangements shown in Figs. 1 to 36 in- clusive. The panels are 90 inches high with framework of pipe or angle iron, as shown in the corresponding figures. The panel ma- terial is black marine-finished slate 2 inches thick, of two sections. All apparatus is of the best grade. The costs includes all apparatus scheduled in Table II, and everything shown in the figures which is not a part of the building construction. 1541 Switchboards For Power Stations 75 Table I — Approximate Cost of Switchboard Panels Fig. Cost ♦U.B.C. Amps. Volts Kind of Panel Volts Amps. Fig. Cost *U.B.C. 1 $ 935 15 500 300 6 600 Generator 2 200 600 19 $ 480 18 500 1 015 12 500 300 11 000 6 600 300 500 15 500 1 835 15 500 300 6 600 Feeder 2 200 600 19 420 18 000 855 12 500 300 11 000 6 600 300 390 IS 500 2 360 7 800 300 6 600 Generator 440 600 20 340 9 800 305 9 200 300 2 200 440 1 200 390 9 800 2 260 7 800 300 6 600 Feeder 440 600 20 290 9 800 255 9 200 300 2 200 440 1 200 340 9 800 3 1 080 15 500 300 6 600 Generator 2 200 300 " 21 360 9 200 . 915 12 500 300 11 000 6 600 300 310 7 800 3 860 15 500 300 6 600 Feeder 2 200 300 21 260 9 200 770 12 500 300 11 000 6 600 300 265 7 800 4 340 9 800 600 440 Generator 2 200 300 22 375 9 200 385 9 800 1 200 440 6 600 300 325 7 800 4 290 9 800 600 440 Feeder 2 200 300 22 280 9 200 335 9 800 1 200 440 6 600 300 285 7 800 6 340 9 800 600 440 Generator 440 600 24 360 9 800 385 9 800 1 200 440 440 1 200 410 9 800 6 285 9 800 600 440 Feeder 440 600 24 310 9 800 330 9 800 1 200 440 440 1 200 "355 9 800 7 475 18 000 600 2 200 Generator 6 600 300 25 370 7 800 490 15 500 300 6 600 2 200 300 320 9 200 7 410 18 000 600 2 200 Feeder 6 600 300 25 275 7 800 385 15 500 300 6 600 2 200 300 270 9 200 8 350 9 200 300 2 200 Generator 11 000 300 26 695 12 500 295 7 800 300 6 600 6 600 300 590 15 500 8 250 9 200 300 2 200 Feeder 11 000 300 26 560 12 500 255 7 800 300 6 600 6 600 300 505 15 500 9 400 9 200 300 2 200 Generator 2 200 600 27 625 18 000 385 7 800 300 6 600 6 600 300 585 15 500 9 360 9 200 300 2 200 Feeder 2 200 600 27 530 18 000 345 7 800 300 6 600 6 600 300 470 15 500 10 400 9 200 300 2 200 Generator 2 200 300 28 270 3 000 375 7 800 300 6 600 2 200 100 240 3 000 10 355 9 200 300 2 200 Feeder 2 200 300 28 230 3 000 345 7 800 300 6 600 2 200 100 212 3 000 11 275 3 000 300 2 200 Generator 2 200 300 29 290 3 000 255 3 000 100 2 200 2 200 100 265 3 000 11 215 3 000 300 2 200 Feeder 2 200 300 29 250 3 000 200 3 000 100 2 200 2 200 100 225 3 000 12 440 9 200 300 2 200 Generator 2 200 300 30 425 9 200 385 7 800 300 6 600 6 600 300 375 7 800 12 345 9 200 300 ; 2 200 Feeder 2 200 300 30 330 9 200 350 7 800 300 ; 6 600 6 600 300 325 7 800 13 480 9 200 300 2 200 Generator 2 200 600 31 535 18 000 420 7 800 300 6 600 6 600 300 560 15 500 13 410 9 200 300 2 200 Feeder 2 200 600 31 465 18 000 405 7 800 300 6 600 6 600 300 440 15 500 15 550 9 200 300 2 200 Generator 2 200 600 33 780 18 000 445 7 800 300 6 600 6 600 300 800 15 500 IS 415 9 200 300 2 200 Feeder 2 200 600 33 705 18 000 425 7 800 300 6 600 6 600 300 680 15 500 16 700 18 000 600 2 200 Generator 6 600 300 34 490 7 800 640 15 500 300 6 600 2 200 300 435 9 200 16 585 18 000 600 i 2 200 Feeder 6 600 300 34 410 7 800 515 15 500 300 6 600 2 200 300 405 9 200 17 550 7 800 300 6 600 Generator 6 600 300 35 710 7 800 500 9 200 300 2 200 2 200 300 675 9 200 17 475 7 800 300 6 600 Feeder 6 600 300 35 635 7 800 475 9 200 300 2 200 2 200 300 600 9 200 18 915 18 000 300 2 200 Generator 11 000 300 36 1 240 12 500 1 825 15 500 300 6 600 6 600 300 1 130 15 500 18 800 18 000 300 2 200 Feeder 11 000 300 36 1 045 12 500 715 15 500 300 6 600 6 600 300 940 15 500 *The column marked U. B. C. gives the ultimate circuit-breaking capacity of circuit-breakers set for instantaneous trip. The above table will permit of obtaining the approximate cost of a complete switchboard. The cost for exciter panels may be taken from pages 34 and 44. 76 Switchboards For Power Stations 1541 The cuts on this and the three succeeding pages include several special arrangements which were designed to meet the requirements of individual installations. Standard arrangements are applicable for most installations and can usually be adopted to good advantage. A few typical standard arrangements are shown on pages 81, 82 and 83. 1541 Switchboards For Power Stations 77 78 Switchboards For Power Stations 1541 1541 Switchboards For Power Stations 79 Fig. 33 Fig. 36 Figs. 28 to 36 — Double Bus, Separate Mounting Arrangements 80 Switchboards For Power Stations 1541 Table II — Schedule of Apparatus for Standard Panels Three-Phase Generator Panel, 16 Inches Wide. 1 Ammeter. 1 Polyphase indicating wattmeter. 1 Field Ammeter. 1 3-way ammeter switch. 1 Synchronizing receptacle. 1 Voltmeter receptacle, 8 pt. 1 Field switch. 1 Rheostat hand wheel. 1 Oil circuit-breaker, non-automatic (single throw, or double throw by means of one or two circuit-breakers as shown in Figs. 1 to 36 inch). 2 Current transformers. 2 Potential transformers with fuses. Disconnecting switches when shown. Three-Phase Feeder Panel, 16 Inches Wide. 1 Ammeter. 1 Three-way ammeter switch. 1 Oil circuit-breaker — automatic (single throw or double throw by means of one or two breakers as shown in Figs. 1 to 36 inch). 2 Relays; single phase, overload, inverse time limit. 3 Current transformers. Disconnecting switches where shown. Details It is of importance to the appearance of the installation, as well as to its fitness as a unit in the electrical system, that all details of construction, such as supports for bus-bars, electrical connections, operating mechanisms, etc., be uniform in de- sign throughout. Fig. 38 illustrates many of various fittings for both pipe and angle frame and for both open and en- closed structures which may be obtained in quan- tities from any large sup- ply house. In designing a structure the arrange- ment of parts should be madetoconform,asmuch as possible, to the ap- plication of the standard n Ln ■■“'ll 1 w-| i ffl'! 1 f Fig. 38— Details of Switchboard Construction for Pipe and Angle Frame Work and Masonry Compartments 1541 Switchboards For Power Stations 81 fittings for the obvious reason that the first cost and cost of spare parts will be minimized, and that advantage is thus taken of the ex- perience of others who have aided in the standardizing of such fittings. Standard Structure Arrangements When ordering remote control switchboard equipments, it is usually possible to effect a saving in time of delivery and in cost, where a station is laid out so that standard structure arrangements can be used. The Westinghouse Electric & Manufacturing Com- pany has standardized various structure arrangements which are ap- plicable to most installations. The following are typical standard arrangements listed in cata- logue section DS1440 for hand-operated remote-control oil circuit- breakers. Fig. 39 — One breaker single-bus without disconnecting switches. Fig. 40 — Two-breaker double-bus without disconnecting swicthes. Fig. 41 — One-breaker single-bus with disconnecting switches. Fig. 42 — One-breaker double-bus with disconnecting switches. 82 Switchboards For Power Stations 1541 Fig. 43 — One-breaker single-bus with disconnecting switches on each side of breaker. Fig. 44 — Two-breaker double-bus with disconnecting switches Figs. 45, 46, 47, 48 — Various wall-mounting arrangements. 1541 ■Switchboards For Power Stations 83 Fig. 50 Fig. 50 — Two- breaker double- bus with discon- necting switches (two-single - bus structures). Fig. 49 Fig. 49 — One-breaker single-bus with disconnecting switches. Fig. 51 Fig. 51 — One-breaker double-bus with disconnecting switches. 84 Switchboards For Power Stations 1541 ' VI THE ELECTRICALLY-OPERATED SWITCHBOARD By C. H. SANDERSON The electrically-operated switchboard usually takes one of three general forms: namely, the panel board (Figs. 2 and 3), the combi- nation control desk and elevated instrument board, (Figs. 4, 5 and 7), or the combination pedestal and instrument post board (Fig. 8). As in the application of self-contained or remote mechanically- controlled switchboards, there is no well defined field to which any of the three forms is confined. More than in any other type of switchboard does the electrically-operated board approach the ideal of the designing engineer, as it is almost entirely uninfluenced by Fig. 1 — Various Forms of Control Switchboards for Electrically-Operated Equipment the form of apparatus which it controls. This fact, moreover, accounts largely for the great variety of combinations, some of which are shown in Fig. 1. There are, however certain general conditions which influence a choice of design and which must be recognized before a satisfactory arrangement can be obtained. The most important of these are: 1 — The capacity of the station. 2 — The number of generator, feeder, bus-tie and exciter circuits to be con- trolled. 3 — The relative proportion of feeders to generator circuits. 4 — The scheme of bus-bars and inter-connections. 5 — The location and arrangements of the switchboard gallery as regards the location and arrangement of the station apparatus. 6 — The first cost and maintenance cost. 7 — The system of operation; or, the usual manner in which the various circuits will be operated, considered together with the provisional arrangements for emergency use, or alternate scheme of operation. 8 — The number and kind of instruments and control devices to be used. 1541 Switchboards For Power Stations 85 Fig. 3 — Rear View of Switchboard Shown in Fig. 2 86 Switchboards For Power Stations 1541 A discussion of the various forms of control shown in Figs. 1 to 8 will illustrate the usual methods in which the relation of the above conditions to the type of board are recognized. The Panel Board The panel board is the least expensive and the simplest in con- struction. It is frequently chosen for plants of moderate capacity, and, occasionally, for those of high capacity where the number of circuits are few and the length of the board is therefore kept with- in a space which may be covered almost instantly by the operator. The panel board is invariably chosen for substations, as it must generally har- monize with, and probably be an ad- dition to the panel board controlling the low-tension alternat- ing and the direct- current circuits. Oft- en the control for the hand - operated and the electrically-oper- ated apparatus of the substation are com- bined on the same panel, thus obtaining a small, inexpensive and simple board. The panel board, although the simplest in construction, may, because of its usually great length where applied to large stations, be much more difficult to operate than the desk control. It usu- ally requires the least width and the greatest length as regards floor space and is, therefore, sometimes chosen in spite of other possible disadvantages, where a long, narrow gallery is the only provision which can conveniently be made for the switchboard. The open construction of wiring and control busses, as obtained by use of the panel board, is alone responsible for its adoption by many en- gineers. 1541 Switchboards For Power Stations 87 It is desirable to arrange the panels to correspond with the wiring arrangement, if possible, as this is of considerable assistance to the operator by permitting the use of a dummy or miniature bus, or system of buses on the front of the panels, thus forming a single line diagram of the complete wiring system. The conduit system for arranging the control and instrument wiring is also greatly sim- plified. If, however, there are a great many circuits to be con- trolled and the arrangement is such that a number of feeders in- tervene between each generator panel, the generator panels become Showing arrangement of meter receptacles and miniature bus. too widely separated to be under the immediate supervision of the operator and must be assembled at one end or at the center of the board or as an entirely separate board. The Control Desk The combination control desk and elevated instrument board as illustrated in Figs. 4 to 7 inclusive, may be used for stations of any capacity and any number of circuits. The particular form chosen, however, must depend upon the local conditions, as above described. For a small number of circuits the linear desk (Figs. 4 and 5) may be employed, while for a greater number of circuits 88 Switchboards For Power Stations 1541 the semi-circular desk (Fig. 7) is more desirable, as it permits a uniform view of all sections of the desk from one central position. When it is desired to use a wall of the building for support- ing the instrument panels, the arrangement may be as shown in Fig. 1-b. The instrument wiring, except for a small amount beneath the desk, and all small, unsightly auxiliaries may thus be’ located in a separate room. Where there are a few instruments and a very compact form of desk is desired, flush type instruments inserted in the top of Fig. 6 Cross Sectional Drawing of Combination Control Desk and Elevated Instrument Board For generator and bus tie circuits, with double semi-circle feeder board of the panel type. the desks, as in Fig. 1-c, or standard instruments supported above the desk as in Fig. 1-d, may be used. The form shown in Fig. 1-e is the next step, where more instruments must be accommodated on the simplest form of board. In this form also the desk portion may be employed for generators only, while the feeders are accom- modated on a continuation of the instrument section extending to the floor and arranged on each side of the generator sections. Fig. 1-f may be employed where many relays and other auxiliaries must also be accommodated. With this arrangement the wiring on 1541 Switchboards For Power Stations 89 all panels may be entirely enclosed, at the same time making it very accessible. When it is considered desirable that the operator have an unobstructed view of the station floor while standing at his board in the gallery the forms shown in 1-g, 1-h, 1-i or 1-j may be Fig. 7 — Circular Type Control Desk Instrument panels supported on columns which form part of the desk framework. adopted. The wiring for the instruments is taken up through the columns supporting the instrument panels, which are covered at the back with expanded-metal or sheet-steel removable covers. The instrument columns. Figs. 1-i, or 1-1, may be arranged to form a part of the gallery railing where desired. Fig. 8 — Combination Pedestal, Post, and Panel Equipment When the number of feeder circuits is very large as compared to the number of generator circuits, a very satisfactory arrangement may be obtained by the use of the arrangement shown in Figs. 1-j 90 Switchboards For Power Stations 1541 and 1-k. In the former, the switchboard is sometimes built in semi-circular form, where there is a great number of panels, so that all meters will face the operator’s desk. The arrangement shown in Fig. 1-k may be used when it is desired to control a great number of circuits in addition to the generator circuits from the control desk itself. The instruments are divided between the front and rear switchboard , the indicating and integrating meters, voltage regulators, testing receptacles, etc., being placed on the front board, with the relays, relay switches, and station auxiliary control which is operated infrequently on the rear board. The ends are covered with grill Fig. 9 — Electrically-Operated Double-Throw Exciter Board Containing double-pole, double-throw switches (panels 1, 3, 4 and 6) for four exciters, and double-pole, double-throw field switches (panels 2 and 5) for six generator fields. work, provided with doors, thus forming an enclosed compartment containing the more unsightly parts of the board. Pedestals and Posts When a station is equipped with very large units, pedestals for the control switches and receptacles, with posts for supporting the instruments, are sometimes used because of the complete indi- viduality thus obtained for each unit. The chance of the operator mistaking the wrong control switches is greatly reduced and the 1541 Switchboards For Power Stations 91 chance of trouble in the small wiring communicating itself to more than one unit is minimized. This form of control may be used for the generators only, and perhaps for the transformer banks when used, while the feeders, which require less attention, are pro- vided with a panel type of board. Fig. 10 — Rear View of Exciter Board Shown in Fig. 9 92 Switchboards For Power 'Stations 1541 VII CONTROL EQUIPMENT OF THE ELECTRICALLY OPERATED SWITCHBOARD By H. A. TRAVERS Control desks and panel boards of the type employed for large power stations contain several features which are foreign to the hand operated boards. While some of these could be applied to the simpler switchboards, if desired, questions of economy, grade of switchboard operator and like factors, make their use inadvisable. In the case of the electrically-operated board, however, controlling, as a rule large-capacity generating units, transformers and feeders, it becomes desirable and essential to provide refinements to the switching equip- ment such that the station attendant may operate his machines to advantage, know exactly what he is doing, and act quickly and cor- rectly and prevent mistakes which might seriously damage large expensive apparatus. The Miniature Bus For the proper and efficient operation of an electrically-operated panel board or control desk of any size, a miniature bus is extremely desirable. It furnishes the operator a bird’s eye view, as it were, of the station wiring, since the miniature bus is a skeleton or single-line diagram of all main circuits of the station, with devices for indicating the relative location of all circuit-breakers, disconnecting switches, generators, power transformers and feeder circuits. . The miniature bus is usually made of polished copper strap run along the top of the desk, or, in case of a vertical board, on the face of the panel. Fig. 1 shows the layout of the miniature bus-bar of a large gen- erating station controlling eight generators. The generators have been grouped in pairs and each pair of generators connects to a local bus; from there to a step-up transformer bank, and then to two high- tension feeders. There is a common low-tension auxiliary bus-bar to which all the generators and transformer banks may be connected if desired, so as to permit any generator of one group feeding a trans- former bank in another group. In a similar manner there is a high- tension tie or auxiliary bus which permits any transformer bank to be connected to any group of outgoing feeders. Attention is called to the simple manner iirwhich the buses have been run by locating the generators and transformers in their respec- tive groups, rather than grouping the generators at one end of the desk and feeders at the other end. The actual location of the circuit- 1541 Switchboards For Power Stations 93 Fig. 2 — Semi-CirculariControl Desk 94 Switchboards For Power Stations 1541 breaker corresponds, of course, to the arrangement indicated by the miniature bus, and by such a layout the amount of current to be carried by any section of the bus is reduced to a minimum, with cor- responding decreased cost for cables from generators to bus struc- ture, etc., and at the same time affording great flexibility in the oper- ation of the system. For stations having two or more circuits of different voltages such as 2200 volts for generators, 11000 volts for local feeders, and 44000 volts or higher for main feeders, it sometimes becomes desir- able to indicate unmistakably the voltage of the different portions of the station circuits. This is readily accomplished by giving the respective portions of the miniature bus different finishes, such as polished copper, mottled oxide copper, nickel, etc. Fig. 2 shows another station in which the generators and trans- former banks are grouped at one end of the desk and the feeders at the other end of the desk. Due to the various auxiliary and tie bus- bars, it is noted that the desk is largely covered by numerous minia- ture bus-bars. In order to distinguish between the different miniature buses on this particular installation, the high-tension and low-tension bus- bars were made in different colors. The low-tension generator bus was finished in polished nickel and is shown in the cut by plain lines. The neutral bus between the transformers was finished in mottled oxide nickel; this is shown on the cut by hatched lines. The main high-tension bus-bars were finished in polished copper and are indi- cated by a solid black line. The high-tension relay buses were finished in mottled oxide copper and are shown in solid black and white lines. Had it not been for the different finishes on these miniature buses a great deal of confusion would have probably resulted in the operation of the plant, in spite of the fact that miniature buses were placed on the desk which are, of course, almost an actual necessity, in order to give the operator any indication of what he was doing. The relative location of circuit-breakers is shown by placing either the dial plate and handle of the controller, or the indicating lamp (usually red) for the closed position of the breaker, directly in the miniature bus. Disconnecting switches are indicated in several ways. One common way, which is the height of simplicity and at the same time rugged and reliable, is to represent the dummy disconnect- ing switch by a small piece of metal superimposed on the top of the miniature bus in its proper relative location. One end of this dummy 1541 Switchboards For Power Stations 95 switch is hinged to a pair of phosphor-bronze clips that are bent toward each other so as to prevent the dummy switch from bein'g turned over without positive ac- tion on the part of the operator. One side of the dummy switch is given a polished copper finish the same as the miniature bus and when this side is uppermost, it of course indicates that the actual disconnecting switch is in the closed position. The other side of the dummy switch is given a black finish and when this side is up- permost, an apparent '‘break” has been made in the miniature bus and indicates that the actual dis- connecting switch is in the open position. Fig. 3 shows a drawl- ing of this switch. 1- ^ 1 , l_ -jj.. J Fig. 3 — Dummy Disconnecting Switch Another method for indicating the disconnecting switches is to insert small telephone switchboard lamps in the miniature bus and run wires to snap switches located near each set of disconnecting switches. The snap switches are turned to the corresponding posi- tion of the disconnecting switches and the correct indication appears on the desk. This method, while more expensive on account of the cost of control wiring, has the advantage of giving more reliable information as to the actual position of the disconnecting switches, since in the other method there is a possibility that the operator at the control desk may forget to set the dummy disconnecting switches in the proper position; or a misunderstanding may arise between the desk operator and the attendant who operates the disconnecting switches. Fig. 4 indicates how these lamps are inserted in the bus. The location of a generator is usually indicated by means of a card-holder placed at the end of the miniature bus strip represent- ing the connections from the gene- rator. Power transformersarein- dicated by breaking the miniature bus and placing two short pieces Lens Fig. 4 96 Switchboards For Power Stations 1541 at right angles to the bus, to represent the high and low tension wind- ings of the transformer, or by putting card-holders in the bus at right angles to it. Feeder circuits are either sup- plied with card-holders at the end of the strip of miniature bus, thus allowing a card to be inserted with the name and number of the par- ticular feeder circuit, or they are tipped with an arrow head. Sometimes both devices are employed. Synchronizing Devices Synchronizing receptacles are placed either directly in the miniature bus at a point corres- ponding to the position of a circuit-breaker used to connect a machine or incoming feeder to the bus-bar, or else convenient!}^ near the con- troller switch of the synchronizing circuit- breaker, thus affording the operator visual in- Fig. 5 — Synchronizing Re- , ceptacie and Plug dicatiou that he IS usiug the proper control switch when synchronizing. The synchroniz- ing schemes usually employed with control desks or electrically- operated panel boards are of such a nature as to interlock the closing circuit of the circuit-breaker through an extra contact on the syn- chronizing receptacle. This prevents the operator from closing the circuit-breaker without first inserting the synchronizing plug into the proper receptacle, and upon so doing the fact is brought forcibly to mind that the particular circuit in question must be operating syn- chronously with the bus-bars before attempting to close the circuit- breaker. Fig. 5 shows the standard type of synchronizing receptacle and plug used largely where machines are to be synchronized to a common bus. Another desirable form of synchronizing outfit is a rotary drum type receptacle which may be turned to the right or left by means of two different removable keys or handles. These two keys are painted different colors, usually red and black, one known as the '‘incoming key” and the other as the “running key.” Both types of receptacle are provided with contacts for synchroscope and also closing coil circuit of oil breaker if desired. To further assist operators and to prevent them from connecting together circuits that have not been properly synchronized, an auto- matic synchronizer may be used to excellent advantage. This instru- ment is essentially a balancing type relay, consisting of a walking 1541 Sivitchboards For Power Stations 97 beam, at each end of which is a solenoid. Each solenoid has two windings, one connected to a voltage transformer energized from the bus-bar or running circuit and the other connected to a voltage transformer energized from theincom- ing circuit. The windings on the solenoids are so re- lated that only when the two circuits are in phase and approximately at synchronous speeds, will the walking beam close an auxiliary contact, which in turn completes the cir- cuit through a suitable relay switch to the clos- ing coil of the circuit- breaker of the incoming Fig. 6 — Automatic Synchronizer machine. Fig. 6 shows a front view of this device and Fig. 7 a diagram for same in connect- ing two generator circuit-breakers. The particular method of synchronizing to be selected, depends largely upon the general scheme of connections involved. In sta- tions where there are but a few machines feeding into a single or double bus that is not sectionalized, the method of synchronizing A C Bus Bars 98 Switchboards For Power Stations 1541 each machine to the bus generally works out to advantage. Where the bus is sectionalized or a ring bus is employed, the method of synchronizing between machines usually gives better satisfaction since it simplifies the synchronizing wiring and reduces to a minimum the number of voltage transformers required. Other Electrically Operated Devices for the Control Desk Besides the control switches for the electrically-operated (gen- erator, feeder, bus-tie and other) circuit-breakers that may be re- quired, there are usually several other electrically-operated devices to be controlled from the desk or board. These are the motor- operated governor for the prime mover, the electrically-operated field-rheostat face-plate, the electrically-operated field switch, etc. In hydro-electric generating stations, controller switches for opera- ting the motor-driven head-gates on the penstock are often added at -the desk. As a rule, indicating lamps are not supplied with these control switches. However, in the case of head-gate motors they are sometimes used to indicate the limits of travel of the gate or the satisfactory operation of the motor. The control switch for the head-gate motors is usually designed so that when thrown to posi- tion for raising the head-gate the switch must be held by the operator during the operation. This prevents the gate from being opened too wide. The reverse connection however can be made and left connected by the operator, the motor being stopped at end of travel by suitable limit switches at the head-gate. This arrangement is desirable as it permits the operator to start the closing of head gates in case of trouble, and then turn his attention to something else of prime importance that is usually occurring at such a time. The governor-motor control switch requires no lamps since the synchroscope and frequency meter give indication as to a change in the speed of the prime mover. Electrically operated rheostat face-plates occasionally have a lamp to indicate a predetermined position for the rheostat arm after the machine has been running and the fields have become heated. Electrically operated field switches are not provided with indi- cating lamps, as the field ammeter gives an indication of whether the switch is opened or closed. Signal Equipment With the present tendency toward large generating units and consequent demand for careful operation, modern electrically-oper- 1541 Switchboards For Power Stations 99 ated desks and boards are frequently provided with a set of signaling devices on the generator sections, whereby the switchboard operator may keep in close touch with the generator room when starting up and connecting in an idle genera- tor or when shutting down a running machine. These signaling devices are duplicated, one set being at the control desk and the other in the engine room near prime mover. The outfit usually consists of from four to six indicating lamps with flush type push-buttons and suitable legends, either on the lenses of the lamps or on the push-button face plate. The legends commonly employed are ‘ ‘ Stand by , ” “ Fast, ” ' ‘ Slow, ” “ Shut Down, ” “O.K., ” “Transfer Load, ’’ and the like. There should also be an additional push-button on the desk which, when held closed, will cause an electrically-operated whistle to blow or gong to ring, thus calling the attention of the engineer to his signal panel. The switchboard operator may then instruct the engineer to start up a new machine and order the speed raised or lowered to expedite synchronizing, the engineer signaling back to the switchboard as soon as he has followed instructions. Fig. 8 shows a signal pedestal for use in the generator room. Figs. 9A and 9B indicate the diagram of connections for such an equipment partly shown by Fig. 8. Meter Equipment The selection of the meter equipment becomes of more impor- tance in an electrically-operated system than on the small boards, for the reason that many more economies can be introduced in the opera- tion of a large station by skilled operators with a suitable meter equipment, than would be possible in a smaller plant. At the same time a multiplicity of meters should be avoided and only those em- ployed which will give most quickly the information desired. Great assistance in determining what particular kinds of meters are desired for the various circuits of the system, may be derived from an inspec- tion of the single-line diagram of main circuits for the plant. With such a diagram one may see at a glance the relative importance of one circuit to another, and what results are desired from the gener- ators, transformers, and feeders. A typical single-line diagram is shown in Fig. 10, with a selection of instruments indicated for each important circuit. For each generator circuit, one ammeter (with Fig. 8 100 Switchboards For Power' Stations 1541 Fig. 9-A — Usual Arrangement Employed for Bell Alarm Circuits Fig. 9-B — Arrangement with Cieneral Signal on Station Wall to (^all Engineer’s Attention to Particular Machine 1541 Switchboards For Power Stations 101 three-way ammeter switch) , one voltmeter, one indicating wattmeter, one field ammeter, and one power factor meter, have been chosen. A bus voltmeter has been provided ; also a frequency meter that may be plugged either to the bus-bars or to any machine. Such a meter equipment will give all the desirable and useful information regarding the operation of the generators that may be required in a generating It It Breakers Shown\^\ are Auto. For reverse power only. Breakers Shown X I are Non- Auto. Fig. 10 plant of moderate or large capacity. In a plant of such size the load on the generators is usually well balanced and, consequently, three ammeters are unnecessary. By means of a three-way switch, the one ammeter may be connected in on any of the three phases as a check on the loading of the generator. The indicating wattmeter gives at once a direct reading of the power output of the generator, 102 Switchboards For Power Stations 1541 and the power factor meter will give instant notice whether or not the operator is getting the most out of the generators by operating all the machines at the same power factor. The field ammeter gives an indication of heating in the generator field and is especially desir- able where automatic voltage regulators are used. In such cases a higher voltage can be applied across the field windings of the gener- ators, than that for whicfi they are designed and under certain con- ditions of load and power factor, the regulator would cause the generators to become unduly loaded, and unless the field ammeter is used as well as the indicating wattmeter, this condition might not be noticed by the switchboard operator. For the transformer circuits of this particular station it is found desirable to use both an ammeter and indicating wattmeter, since the transformer bank cannot be treated as a unit with the generators. For the feeder circuits, three ammeters have been provided, since the ammeter load is usually the determining factor and a ground on one line, unbalanced loading, etc., can be most readily noticed. Watt- hour meters are desirable in that they give a record of the power transmitted over each feeder. Other indicating meters may be added if conditions warrant, such as power factor meters, compen- sated voltmeters, and the like. Relay Equipment This portion of the control equipment for a large power station assumes a degree of importance not usually found necessary in the small capacity stations. With large amounts of power concentrated at one locality it is essential that suitable and reliable relays be em- ployed to safeguard and maintain continuity of operation, cutting off from the system such apparatus or circuits that show signs of distress, without interfering with the rest of the system. Consider- able development in the last few years has now brought on the market a collection of relays that are reliable and positive in operation, simple in design, and of rugged construction, thus affording means of protecting any system, large or small. No attempt will be made in this article to cover the design features of the various relays but rather their application and limitations. Referring to Fig. 10 it will be noted that relay equipments as well as the meters have been indicated for the various circuits. In the generator circuits there have been indicated reverse-power relays which will cut off a generator from the bus-bar in case of an internal short circuit or other source of trouble, such as throwing a dead machine on bus-bars by mistake, which would cause the remaining generators to feed into the one in trouble. 1541 Switchboards For Power Stations 103 Some operators also favor the use of overload relays in generator circuits when the generator is being synchronized to the system, in order to avoid possible trouble due to a mistake of the operator, throwing the generator on the bus when the incoming machine is not in synchronism with the running machines. Of course the generators that are running should not have the overload relays connected to the tripping coils of the circuit-breaker. The temporary relay con- nection is made by means of extra contact points on the synchro- nizing receptacle and plug so that only when the plug is inserted in the receptacle will the relay trip-circuit become operative. In some cases a single overload relay is connected in each gener- ator circuit with its tripping circuit connected to an indicating lamp on the control desk, or an alarm bell, or both, for the purpose of warning the station operator that the generator is overloaded and that another unit must be put into service. For protection of transformer banks, either straight overload inverse-time-limit relays, or differentially connected overload relays are usually employed. If the former are used the design of the relay should be such that it can be set so as to trip the transformer circuit- breaker in case of sustained overload ; but at the same time selective action should be obtained so that in case of a short circuit on one of two or more feeders connected to the transformer, the circuit-breaker of the defective feeder will come out before the transformer breaker, and thereby prevent loss of power on the remaining feeders. As the bellows type of inverse-time-limit overload relay gives practically instantaneous action under short-circuit conditions it is obvious that such types of relays are not suitable and the induction type of relay that can have its minimum time setting adjusted within a range of 0.1 to at least 2 seconds should be used. This type of relay will give the familiar inverse-time action of the bellows type of relay down to one or two seconds, as may be determined by proper relay adjustment, and any increase of current, such as obtains during short- circuit conditions, will not cause the relay to ^ trip till after the prede- termined setting, thus allowing the relays in the |. feeder circuit to act first. ^ . In short, this relay is a § , combination of inverse- time and definite - time ^ wo zoo 300 400 soo 600 too 800. 900 looo /too 1200 m misoo 1 T— 1 Percent of Norma! Relay Current Setting. relays, hig. 11 shows ^ 104 Switchboards For Power Stations 1541 the typical curves for the straight inverse time-limit relay of the bel- lows-type, and the induction type relay, respectively. Each relay gives the inverse time element feature down to 2 seconds for 300 per cent load on the relay for a given setting; but it will be observed that the induction relay permits greater selective action since the curve is not so steep as for the bellows type. Also the induction relay will not become instantaneous at 500 per cent load as is the case with the bellows type. As indicated in Fig. 10 the transformer bank for this station has been provided with instantaneous differentially connected overload relays. The relays are inoperative under any condition of load so long as there is no breakdown in the transformer itself, since the relay is connected to current transformers in both the primary and second- ary side of the power transformer banks, the connections of the relays to the current transformer being such that only when a difference exists in value of the secondary current of the current transformers will the relays operate. See Fig. 12 for diagram of connections of current transformers and relays. Obviously such condition cannot Fig. 12 — Connection for DiiTerentially Connected Instantaneous Overload Relays, to Protect Against Break-Down in Transformer Windings. 1541 Switchboards For Power Stations 105 obtain unless there is a breakdown in the winding of the power trans- former. In such an event the relays operate and trip out the circuit- breakers on both sides of the transformer and cut it off from the system. The feeder circuits are provided with straight inverse-time-limit overload relays. These may be either of bellows or induction type, depending upon whether minimum time eleriient of 2 seconds or less is required under' short-circuit conditions. Fig. 13— Relay Equipment to Prevent the Circuit-Breakers from Opening in Case of Grounds. In stations employing duplicate transmission lines and having the neutrals on high-tension side of the transformers grounded through a resistance, it is often desirable to provide a special relay equipment for maintaining continuity of service on the feeders. This consists of a special instantaneous circuit-opening relay con- nected to a current transformer in the neutral ground circuit which will operate on any current from 2 per cent to full load of the trans- former bank. In case of a broken wire, arcing ground, etc., this relay will open the tripping circuit of the straight overload relays and prevent the feeder breaker from opening. If the source of trouble continues for any length of time then the operator has time to cut in the parallel feeder and manually cut out the defective feeder. In case of an arcing ground which usually burns itself out, the relay will automatically restore the connections of the overload relays. In event of a three-phase short, the relay in the neutral 106 Switchboards For Power Stations 1541 circuit would of course be inoperative and the overload relays would trip out the feeder breaker at once. Fig. 13 shows diagram of con- nections for this relay equipment. The relay equipment for the local service feeder supplying power to the exciter-motor-generator set, etc., has been equipped with definite-time-limit relays in order to prevent this breaker coming out due to a momentary short circuit on some local feeder or sudden over- load such as starting up of an induction motor. It is apparent that the exciter system should not be subject to interruption unless actual dam- age to the exciters would result, as it is, of course, most imperative that the generators be kept excited as long as possible, unless abnormal conditions exist. The tie-bus breakers have obviously been made non-automatic, since these circuits are merely “by-passes” and the proper protection has already been provided in the main circuits. In some installations tie-bus breakers are inserted in the main bus-bars between groups of generators and normally short-circuit bus-reactance coils. These breakers are then made very quick acting and are provided with instantaneous direct-acting trip coils, energized from current trans- formers in the main bus-bars. Should a short circuit occur in one section of the bus-bar, these breakers would immediately open and cut-in the bus-reactance which will prevent the generators on the other sections of the bus from feeding into the short circuit and also prevent loss of voltage on the feeders connected to the sections of the bus-bar not in distress. 1541 Switchboards For Power Stations 107 VIII CIRCUIT-BREAKER STRUCTURE ARRANGE- MENTS FOR ELECTRICALLY-OPERATED STATIONS By H. A. TRAVERS As indicated in the first few paragraphs of these papers the electrically-operated board is usually employed for stations of large capacity requiring heavy breakers not easily closed by hand, or where the design of the station is such that hand-operated remote-control breakers cannot be used to advantage due to the excessive lengths of operating rods required. All the advantages gained by the use of hand-operated remote- mechanical-control breakers over switchboard-mounting: breakers are applicable to the electrically-operated breaker installations. As stated under discussion of the remote-hand-operated boards, the space required for breakers and bus-bars for a given capacity will be practically identical, but due to the absence of operating rods, bell cranks, etc., arrangements and designs of structures can be used that are not possible otherwise and that present various adaptations to certain desirable building designs, which are out of the question with hand-operated remote-control breakers. This is particularly evident in large stations where high-tension voltages such as 2400, 6600 and 11000 are used for generators, and where extra high-tension voltages such as 22000, 44000, 66000, etc., up to 150000 are employed for distributing circuits. The variety of structure arrangements with electrically-operated circuit-breakers is almost unlimited, but good operating practice has evolved certain typical designs which are illustrated in the following cuts and a brief discussion will be given for each arrangement shown. In general it may be stated that there are six general types of structure arrangements in use. (1) Wall mounting — All apparatus and bus-bars either mount- ed directly on or supported from a wall of the building. (2) Frame work mounting — all apparatus and bus-bars mount- ed on a framework of iron pipe or structure steel shapes. (3) Combination wall or framework mounting. (4) Concrete or masonry structure mounting — all apparatus mounted in cells. (5) Combination concrete and structural mounting — circuit- breaker in cells, with bus-bars, etc., on iron framework. 108 Switchboards For Power Stations 1541 (6) Floor mounting and structural mounting — circuit-breakers set on floor, with bus-bars, etc., mounted on iron framework. It will be noted that the first five general types of structure arrangements are parallel to those mentioned in the article on re- mote-mechanical-control switchboards. The sixth arrangement ap- plies particularly to high voltage layouts of 22000 volts and above, using the floor-mounting type of circuit-breaker. The same reasons for selecting a given type of structure should be observed as have been outlined under the hand-operated remote- mechanical-control switchboards. The factors involved are identical. The following illustrations show the use of the solenoid-operated circuit-breakers entirely, and have not considered motor-operated breakers. It will be noted that breakers of relatively small ultimate k.v.a. breaking capacity and of voltages up to 13200 and having a single frame for all poles with a single tank, have the solenoid mech- anisms fastened directly to the frame of the circuit-breaker. This makes the breaker a more or less self-contained unit. The remaining breakers which are built with each pole a separate unit with its own frame and tank are operated from one solenoid acting on a common operating mechanism to which each pole is connected. Figs. 1 to 4 show typical structures both for single-throw and double-throw bus systems, with disconnecting switches either on one side of the breaker or on both sides, for installations for voltages up to 6600 and of relatively small capacity. As will be noted these breakers have the self-contained solenoid mechanism as part of the circuit-breaker framework. Fig. 1 shows a one-breaker single-bus structure with disconnecting switches between the bus and the breakers. Fig. 2 shows the one-breaker double-bus structure with 1541 Switchboards For Power Stations 109 disconnecting switches between the bus and breaker. Fig. 3 shows a one-breaker single-bus structure with disconnecting switches on either side of the breaker. Fig. 4 shows a two-breaker double-bus structure with disconnecting switches on either side of the breaker. Figs. 7-8 Fig. 7 Fig. 8 no Switchboards For Power Stations 1541 Figs. 5 to 8 show the next size frame breaker which has all poles in one frame but separate tanks for each pole. This breaker, being heavier, makes it desirable to have the solenoid mechanisms remote from the breaker, as shown. This type of breaker can be used with voltages as high as 22000 where the total station capacity is small enough so as not to require the use of a cell structure for the breakers. The structure shown in the cut is limited to 13200 volts however. Figs. 9 to 12 show the open type of structure similar to the pre- vious figures and the same voltage class of service as indicated for Figs. 5, 6, 7 and 8. The essential difference in this structure being, of course, the use of breakers having a separate frame and tank for each pole with all poles operated from a single solenoid by means of a suitable countershaft. While the breakers shown in these figures are suitable for voltages up to 22()()(), depending upon the ampere capacity, it is the intention with this arrangement of structures to limit the operating voltage to 13200 volts, as has been indicated by 1541 Switchboards For Power Stations 111 the type of disconnecting switch and current transformer shown. The use of a breaker suitable for a much higher voltage than the operating voltage is very often resorted to in order to obtain suffi- cient breaking capacity on account of the total installed k.v.a. of synchronous machines. As stated in the first article, the ultimate k.v.a. breaking capacity of a given circuit-breaker may be increased approximately 1 per cent for every 1 per cent decrease in voltage from the rated voltage on the breaker. Fig. 15 112 Switchboards For Power Stations 1541 Fig. 16 Figs. 13 to 16 illustrate the use of the same breakers as have been shown previously except that they are mounted on the side of the station wall and may, if desired, be enclosed by cells of concrete, soapstone, asbestos lumber, or other suitable material. Figs. 13 and 14 show the small type of breaker with self-contained solenoid mechanisms for either single or double bus-bars with disconnecting switches between the breaker and the bus. Fig. 15 shows the two- breaker double-bus structure, with one breaker and bus mounted on either side of the wall. Fig. 16 shows the larger frame breaker, having separate tank and frame for each pole, with the bus-bars attached to braces fastened to the wall and the breaker mounted on a suitable pipe framework very close to the wall. If this breaker is to be enclosed in a cell structure a slightly modified form is used as shown in Fig. 17. rig. 17 1541 Switchboards For Power Stations llv3 Figs. 18 and 20 show the concrete or masonry type of structure using the small circuit-breakers which have a single frame for all three poles, with either the self-contained solenoid mechanism as per Fig. 18 or the separate solenoid mechanism as shown in Fig. 20. If desired the three poles of the smaller sizes of the individual-pole breakers may be mounted in a single cell similar to the figures, in which case the breakers would be mounted on the rear wall of the structure in order that the total depth, dimension C, would remain the same. Of course dimension D, the width of the cell structure, would be increased somewhat. It is usually the practice, however, to use sepa- rate cell compartments for each pole when this type of breaker is used, as illustrated in the following figures. Fig. 18 shows a one- breaker single-bus structure with disconnecting switches on either side of the breaker. Fig. 19 shows the arrangement for a two- breaker double-bus structure. It will be noted that the current transformer is to be located underneath the floor at the point where the tie connection between the two breakers has been made. Fig. 20 shows a one-breaker double-bus structure with disconnecting switches on either side of the breaker. Figs. 21 to 24 have been shown to indicate the adaptability of the solenoid-operated circuit-breakers of different sizes and capacity to the same type of circuit-breaker structure. Fig. 21 indicates the type of breaker having the single frame with either a common tank for all poles or a separate tank for each pole, with the solenoid mechan- 1541 114 Switchboards For Power Stations ism placed above the breaker. These breakers belong to the first two classes on page 13 in the first article. Fig. 22 shows the heavy capacity type of breaker designed particularly for cell mounting with a single frame or base for the operating mechanism. These breakers are for voltages from 2200 to 22000 and have a k.v.a. breaking capac- ity ranging from 35000 to 70000. Fig. 23 shows a smaller type of cell mounting breaker and has a breaking capacity ranging from 16000 to 40000 k.v.a. Fig. 24 shows one of the heaviest breaking capacity breakers on the market of the cell type. This breaker has a breaking capacity of 80000 to 100000 k.v.a. and an ampere capacity of 600 to 4000 amperes. As may be noted these four different types of breaker can l)e placed in the same structure without any change in the struc- ture design, and this feature becomes particularly dcvsirablc in many 1541 Switchboards For Power Stations 115 cases where, by means of suitable relays in connection with the breakers, a somewhat smaller or less expensive breaker may be used on certain circuits of the system, such as generators where the breakers are usually non-automatic; whereas in the case of the feeders having automatic breakers, a heavier breaker is necessary on account of it’s having to open under a short circuit. Figs. 25 to 27 show the various combinations possible, using the type of circuit-breaker structure illustrated by Figs. 21, 22, 23, and 24, any of these breakers being adapted to the arrangement shown in these outlines. Each cut shows anywhere from four to 116 Switchboards For Power Stations 1541 Fig. 26 six different arrangements as indicated by the letters A, B, C, D, E and F, the arrows emanating from these letters showing just what is included under that sub-arrangement. Fig. 25-A shows a one- breaker single-bus structure with all main leads from below; hig. 25-B shows a two-breaker double-bus structure with all main leads from below. With such an arrangement the leads from both breakers will be tied together underneath the floor at the points indicated by the horizontal dotted connections. Fig. 25-C is a one-breaker single- 1541 Switchboards For Power Stations 117 bus structure with all main leads from above ; Fig. 25-D is a two-breaker double-bus struc- ture with all main leads from above, the tieconnectionsbeing indicated by the dotted hori- zontal connections directly un- derneath the second floor. Fig. 25-E is a two-breaker double- bus structure with the struc- tures arranged one above the other on separate floors, all main leads leaving from the tie connections between the tw'o structures. It will be noted that this arrangement is a combina- tion of‘A”and‘ ‘C.” Fig.25-F is a one-breaker single-bus structure, with two rows of cir- cuit-breakers arranged one on either floor. The leads would leave from below on the upper floor, and from above on the lower floor. A duplicate struc- ture has been indicated in dotted lines and may be used for a two-breaker double-bus system. Fig. 26-A is a one-breaker single-bus structure with all main leads from below, having the bus-bars and voltage transformers on the upper floor and the circuit-breaker with the disconnecting switches on the lower floor. Fig. 26-B is a two-breaker double-bus structure same as indicated for the “A” arrangement. Fig. 26-C is a one-breaker single-bus structure with all main leads from above, the breaker with the disconnecting switches being on the second floor and the bus-bars and voltage transformers on the ground floor. Fig. 26-D is a two-breaker double-bus structure corresponding to the single-bus structure. Fig. 26-E is a two-breaker double-bus struc- ture using four floors, instead of two as mentioned above for the “D” arrangement. Fig. 27-A shows a bus compartment on the floor above the cir- cuit-breaker structure, with all main leads from below. Fig. 27-B Fig. 27 118 Switchboards For Power Stations 1541 Fig. 28 shows.thebuscompartmenton the floor below the breaker with all main leads from above. In the “B” arrangement note that the disconnecting switches and the voltage transformers in the bus compartment structure would be interchanged in position. Fig. 2 7-C shows a two-breaker double- bus structure with the bus com- partment on the floor between two rows of breakers ; one row of break- ers is on the first floor and the other on the third floor. The breakers on the first floor have the leads come from below and the breakers on the third floor have the leads come from above. The voltage trans- formers in the bus structure would be replaced by disconnecting switches for use with the top row of circuit-breakers. Fig. 27-D shows the bus compartment on the same floor as the breakers. The leads may be from above or below as de- sired according to the location of the dis- connecting switches and the connections from the breaker to the bus. In the illus- tration the disconnecting switches are shown at the top, which would indicate that the leads to the breaker would come from below. The voltage transformers may be placed underneath the bus com- partments where space is available, although they are not shown. Fig. 28 shows a typical layout for cir- cuit-breaker and bus structure for 22000 volts using the pipe-frame-mounting type of circuit-breaker. This arrange- ment shows a single-bus system with the outgoing line breakers in one row having disconnecting switches on either side of the line breakers, and transformer break- ers in the other row with disconnecting switches between the bus and breaker only. Figs. 29 to 33 show various arrange- ments of floor mounting circuit-breakers 1541 Switchboards For Power Stations 119 Fig. 32 Fig. 31 120 Switchboards For Power Stations 1541 for high-tension structures of 22000 volts and upward. Fig. 29 shows an arrangement for a one-breaker single-bus system with disconnect- ing switches on either side of the breaker, if desired, when a long rectangular space is available. Fig. 30 shows an arrangement for a one-breaker single-bus layout where a wider space is available and thereby cuts down the total length of the high-tension room by plac- ing the breakers in two rows. Fig. 31 shows an arrangement for a one-breaker double-bus system. Fig. 32 shows a two-breaker double- bus system suitable for use with a long narrow room. Fig. 33 shows an arrangement for a two-breaker double-bus system where a wider and shorter room is available. Figs. 34 to 36 show typical switching bays of power stations with high-tension power transmission. Fig. 34 is a layout which is very common to water power plants where a long narrow space is avail- able. This, of course, is the usual layout for hydro-electric power stations. The transformer bays are arranged with openings into the 1541 Sii'itchboards For Power Stations 121 generator room to permit rolling out the transformer in case repairs are necessary. Fig. 35 is another modification of this layout with the low-tension breaker structure on the same floor with the trans- formers. This arrangement, as will be noted, obviates the use of an addition to the power house for the high-tension room. Both Figs. 34 and 35 indicate the use of a two-breaker double- bus system on the low- tension side and a two-breaker double-bus Fis- 34 system on the high-tension side. In Fig. 35 the power transformers are to be removed through the generator room. The same was indicated in Fig. 34. Fig. 36 shows a still different arrangement of the same layout where a wider building is available and, in this case, it will be noted that the low-tension circuit-breaker structure has been divided and one bus with its breakers located on the upper floor, with the second bus and breakers on the lower floor. In this case the power trans- former banks are removed directly to the outside of the building on a track as indicated. Such an arrangement is extremely desirable where the ground space is available, as it lessens the cost of the power station, since, if it is necessary to remove the power transformers Fig. 35 Fig. 36 122 Switchboards For Power Stations 1541 through the generator room, necessarily waste space has to be roofed which otherwise can be eliminated. While it would be possible to give a great many other different arrangements, they all more or less are based upon the layout shown in the above cuts. Consequently, it would not be of material value in an article of this nature which must necessarily cover the general features of design whereas each particular station requires individual treatment. In connection with the last three layouts, it will be noted that the lightning-arrester equipments have not been shown. It usually works out to advantage to either place these arresters on the ground alongside of the building or mount them on the roof of the high- tension room in a convenient location to the roof outlet bushings. Where weather conditions will permit, it is recommended that the entire arrester be placed out of doors, as this obviously saves a con- siderable amount of floor space. However, where temperatures of — 15 degrees Centigrade are apt to exist for any length of time, the arrester tank may be placed indoors but the horn gaps can still be left outside. Such an arrangement, of course, means the use of three additional roof outlet bushings in case of a three-phase system or four in the case of a two-phase system; but, as a rule, the extra cost of these roof outlet bushings is considerably less than would be the cost for the larger building necessary to provide sufficient space above the horn gaps of the arresters in case they were placed inside the building. 1541 Switchboards For Power Stations 123 SOME EXAMPLES OF WESTINGHOUSE CIRCUIT- BREAKERS AND SWITCHBOARDS Type F-1 Oil Circuit-Breakers. Three-Pole Single-Throw 300-Ampere 4500-Volt, Panel-Frame-Mounting Type F-2 Oil Circuit-Breaker. Mul- tiple-Single-Pole Single -Throw 500 - Ampere 7500- Volt, Indoor Hand - Operated Remote- Control Pipe-Mounting Type F-3 Oil Circuit-Breaker. Three- Pole Single-Throw 800- Ampere 4500- Volt, Indoor Hand-Operated Switchboard Mounting (Tank Removed) Type F-2 Oil Circuit - Breaker, Three -Pole Double-Throw 600-Ampere 7500-Volt, Hand- Operated Switchboard Mounting (Tank Removed) 124 Switchboards For Power Stations 1541 Type B-2 Oil Circuit-Breaker. Four-Pole Sin- gle-Throw 2000-Ampere 7500-Volt, Hand- Operated, Wall-Mounting (Tank Removed) Type B-3 Oil Circuit-Breaker. Three-Pole Single-Throw 300-Ampere 23,000- Volt, Switchboard-Mounting Type E-9 Oil Circuit-Breaker. 'Phree-Pole Single-Throw 1200-Ampere 13,200-Volt, Electrically Operated Horizontal- Pipe- Frame- Mounting Type F-3 Oil Circuit-Breaker. Three-Pole Sin- gle-Throw 500-Ampere 13,200-Volt, Indoor Electrically-Operated Wall-Mounting Automatic 1541 Switchboards For Power Stations 125 c C S £ -o ^ o « C5 o > u Q s m o S «t ^ Di C n ^ S o .t: u -c > a; :> o> .-iS 2 3 C i! o cc li S "O 0 » •a" c 2 3 hi g ft u o 2 a aw ^ o ^ ^ .S -o ^ g 2 S 2 CO a: ® •ot ^ 2 |gl 0^3 £•0 1 - c ^ o ^ ’C - 0 ® tj .S rjJ O •5 o 'o h 2 S £ £ S CO V ' a ll 5l .2 o ® •o ‘S 3 a a u w V a >> H 126 Switchboards For Power Stations 1541 Type C-2 Oil Circuit-Breaker. Three-Pole Electrically-Operated Vertically-Arranged Leads, 2000 Amperes 15000 Volts. Front View Showing Breaker in Open Position With Two Doors and One Tank Removed. (Breaker Shown Mounted on Structure) 1541 u U 01 _ & c fl o 5 c C< o £ ^ £ S o J « (y a a a |.S? S s • • 3 a £ "o CQ « .« Ul 3 0 * 3 a .b o u L Switchboards For Power Stations 128 Switchboards For Power Stations 1541 a, H a CC •- V C O 3 ' > 3^ iL SI o -s U 0 ) 0 ) if g « § « s .1= § s a 3 (N ^ a z: a 21 - 7 W >, 1541 Switchboards For Power Stations 129 0) 0 < ' 6 3 ^ t © =« T3 ® — < 9 > (N — (/3 -H 0 ) o oj U 0 u CL. .S « 1 I « 2 J £ j3 cz! oa ’o" . . 2 a a ^ a> ft S Ui O ^ CQ ' Cf5 7 ^ o k. ^ ’O h ® "Si « s ^ ^ 9 ij’S o 3 ft ffi ^ k. « O "1 jt a C3 O £ > oa © u « V © a rc >> h 130 Switchboards For Power Stations 1541 Reactance Type, 300-Ampere, 110,000-Volt Oil Circuit- Three-Pole Reactance Type, 1200-Ampere and Type C-1 600-Ampere, Breakers and Disconnecting Switches, Lehigh 15000-Volt Oil Circuit-Breakers, All in Same Structure. Navigation Electric Co., Hauto, Pa. Lehigh Navigation Electric Co., Hauto, Pa. ; Type CD Carbon Circuit-Breaker. Two-Pole 100-Am- i pere 600-Volt with Separate Closing Handles and Common Trip, One Under-Voltage, and Two Overload Tripping Coils j Type CA Carbon Circuit-Breaker. Three-Pole 8000- j Ampere 25-Cycle 500-Volt, Electrically Operated Non- Automatic Type CA Carbon Circuit-Breaker. Four-Pole 800- Ampere 250-Volt with Inverse-Time-Element Dash Pots and Self-Contained Reverse-Current Tripping Attachment on Two Outer Poles Type CA Carbon Circuit-Breaker. Single-Pole 24000- Ampere 750-Volt, Electrically-Operated operated Circuit-Breakers 1541 Sivitch hoard's For Power Stations 133 Vertical Switchboard, Controlling Incoming 66000-Volt Line and 11000-Volt and 2400-Volt Feeders and Battery Charging Equipment. Albina Substation, Northwestern Electric Co. Fifteen Panel Switchboard Controlling 11, 000- Volt Incoming Lines and Feeders and 23000-Volt Feeders. Municipal Plant, Cleveland, Ohio Switchboards For Power Stations 1514 "S ■ot G -2 ^ CO O 1541 Switchboards For Power Stations 135 Switchboard for Michigan Northern Power Co., Sault Ste Marie, Mich., Controlling 4400-Volt Generators and Feeders. (Two Generators Controlled from 18-Inch Wide Panels) Control Gallery and Desks of Engleside Substation, Edison Electric Co., Lancaster, Pa. Desks from Left to Right are 11000-Volt, 60 Cycle; 11000-Volt 25-Cycle; 2300 Volt, 25-Cycle. Vertical Board Contains Local Service and Recording Meters. Battery Charging Set Shown in Foreground WESTINGHOUSE ELECTRIC & MFC. CO. EAST PITTSBURGH, PA. DISTRICT SALES OFFICES City Building Street ATLANTA. GA. . . . Candler 127 Peachtree BALTIMORE, MD. . . Westinghouse 121 E, Baltimore BIRMINGHAM, ALA. . . Brown-Marx 1st Ave. and 20th BLUEFIELD, W. VA. . Kelley-Moyer .... Raleigh & Higginbotham Ave. BOSTON, MASS. . . Rice 10 High BUFFALO, N. Y. . . Ellicott Square Ellicott Square BUTTE, MONT. . . . Montana Electric Co ... . 50-52 East Broadway CHARLESTON. W. VA. . Union Trust CHARLOTTE, N. C. . . Commercial Bank, Rooms 409-10-1 1 Cor. Tryon & Fourth CHATTANOOGA, TENN. . Hamilton National Bank CHICAGO, ILL. . Conway 1 1 1 W.Washington CINCINNATI, O. . . . Traction 5th & Walnut CLEVELAND, O. . . Swetland 1010 Euclid Ave. COLUMBUS, O . . . Interurban Terminal 3rd & Rich ^DALLAS, TEX. . Cotton Exchange Akard & Wood DENVER, COL. Gas & Electric 910 15th DES MOINES, I A. . , Fleming . 21634 6th Ave. DAYTON. O. ... Reibold Main DETROIT, MICH. . . Dime Savings Bank Fort & Griswold *EL PASO, TEX. . Mills . ' Oregon & Mills INDIANAPOLIS, IND. . . Traction Terminal Illinois & Market JOPLIN, MO. BaSom 418 Joplin KANSAS CITY, MO. . Orear-Leslie 1012 Baltimore Ave. LOUISVILLE, KY. . . Paul Jones 312 4th Ave. LOS ANGELES, CAL. . I. N. Van Nuys . . ' . . 7th & Spring MEMPHIS. TENN. . Exchange 6 N. 2nd MILWAUKEE, WIS. . First National Bank 425 E. Water MINNEAPOLIS, MINN. Met. Life Insurance 119-131 S. 3rd NEW ORLEANS, LA. . Maison Blanche 921 Canal NEW YORK, N. Y. . . City Investing 165 Broadway PHILADELPHIA, PA. . . Widener 1325-1329 Chestnut PITTSBURGH, PA. . Union Bank 306 Wood PORTLAND, ORE. . Northwestern Bank .... Broadway & Morrison ROCHESTER, N. Y. . Chamber of Commerce 1 19 E. Main ST. LOUIS, MO 300 N. Broadway SALT LAKE CITY, UTAH . Walker Bank 2d, South & Main SAN FRANCISCO, CAL. . Electric 165 Second SEATTLE, WASH. Alaska 2nd and Cherry SYRACUSE, N. Y. . . University 120 Vanderbilt Square TOLEDO, O Ohio '. . • Madison Ave. & Superior WASHINGTON. D. C. . . Hibbs 723 15th N. W. WILKES-BARRE, PA. Miners’ Bank *W. E & M. Co. of Texas. Service Department Repair Shops Ati..\nta, Ga. Mangum and Markham Streets New York, N. Y. . .512 West 23d Street Boston, Mass. . . 37 Wormwood Street Phil.; oelphia. Pa. 214-220 North 22nd Street Buffalo, N. Y. . . 6 and 8 Lock Street Pitt: burgh. Pa., Arnberson Ave. & P. R. R. Chicago, III. . . . 32 So. Peoria Street S.\n 'rancisco. Cal. . 1400 PMurth St. Los Angeles, Cal. . . 2026 Bay Street Seattli. Wash. . 560 First Ave., South WESTINGHOUSE ELECTRIC EXPORT COMPANY NEW YORK OFFICE— 165 Broadway, New York C’Ty, N. Y. London Office — No. 2 Norfolk Street Strand Japan — Takata & Company, Tokio Chile — J. K. Robinson, Iquique, Chile Brazil — F. H. Walter & Co., Rio de Janeiro, for Northern Brazil Byington & Co., Sao Paulo for Southern Brazil Colombia — Vincente B. Villa, Medellin Venezuela — H. I. Skilton, 520 National Bank of Cuba Building, Havana, Cuba Porto Rico — Porto Rico Railway, Light & Power Co., San Juan, Porto Rico Cuba — Westinghouse Electric Export Co. 520 National Bank of Cuba Building, Havana, Cuba. Co.STA Rica and Nicaragua — Purdy Engineering Co., San Jose, Costa Rica Salvador — W. C. McEntee, Santa Ana, Salvador European and Asiatic Russia — Russian Electric Co., Dynamo, Petrograd, Russia Mexico — Compania Ingeniera, Importadora y Cnntratista, S. A., City of Mexico (Successors to G. & O. Braniff & Co.) FOREIGN COMPANIES Canadian Westinghouse Company, Ltd., Hamilton, Ontario The British Westinghouse Electric & Manufacturing Company, Ltd., Manchester, England For the United Kingdom and her Colonies (except Canada) Germany, Austria and Russia Westinghouse Norsk Elektrisk Aktieselskap — Prinsens Gate 21, Kristiania, Norway For Norway and Sweden SociETE Anonye Westingpouse, Paris, France For France, Belgium, Spain, Holland, Switzerland, Portugal, their colonies and countries under their protectorate The Westinghouse Electric Company, Ltd., Norfolk Street, .Strand, London, W. C. gociETA Italiana Westinghouse, Vado Ligure, Italy For Italy ‘U'-‘