CHAPTER XXIV CONCLUSION 254. Numerous apparatus, structural features and principles have been invented and more or less developed, but have fOQMJ a limited industrial application only, or arc not used at all, l>e- cause there is no industrial demand for them. Nevertheless B knowledge of these apparatus is of (treat importance to the elec- trical engineer. They may bo considered as filling the storehouse of electrical engineer inn, waiting until they are needed. Wry often, in the development of the industry, a demand arises for certain types of apparatus, which have been known for many years, but not used, because they offered no material advan- tage, unlil with the change of the industrial conditions their use became very advantageous and this led to their extrusive application. Thus for instance the com mutating pole ("interpole") in direct-current machines has been known since very many years, has been discussed and recommended, but used very little, in short was of practically no industrial importance, while now practically all larger direct-current machines and synchronous converters use commutating poles. For many years, with tin- types of direct-current machines in use, the advantage of tin commutating pole did not appear sufficient to compensate to* the disadvantage of the complication and resuliunt increase o4 size and cost. But when with the general introduction of tin- steam-turbine high-speed machinery became popular, and lij(ilii-i - speed designs were introduced in direct-current machinery also, with correspondingly higher armature reaction and greater Deed of commutation control, the use of the commutating pole became of material advantage in reducing size and cost of apparatus, and its general introduction followed. Similarly we have seen the three-phase transformer find gen- eral introduction, after it had been unused for many years; so also the alternating-current commutator motor, etc. Thus for a progressive engineer, it is dangerous not to be fjuuil- iar with the characteristics ^iiit! possibilities of the known but 472 CONCLUSION 473 unused types of apparatus, since at any time circumstances may arise which lead to their extensive introduction. 255. With many of these known but unused or little used ap- paratus, we can see and anticipate the industrial condition which will make their use economical or even necessary, and so lead to their general introduction. Thus, for instance, the induction generator is hardly used at all today. However, we are only in the beginning of the water- power development, and thus far have considered only the largest and most concentrated powers, and for these, as best adapted, has been developed a certain type of generating station, compris- ing synchronous generators, with direct-current exciting circuits, switches, circuit-breakers, transformers and protective devices, etc., and requiring continuous attendance of expert operating engineers. This type of generating station is feasible only with large water powers. As soon, however, as the large water powers will be developed, the industry will be forced to proceed to the development of the numerous scattered small powers. That is, the problem will be, to collect from a large number of small water powers the power into one large electric system, similar as now we distribute the power of one large system into numer- ous small consumption places. The new condition, of collecting numerous small powers — from a few kilowatts to a few hundred kilowatts — into one sys- tem, will require the development of an entirely different type of generating station: induction generators driven by small and cheap waterwheels, at low voltage, and permanently connected through step-up transformers to a collecting line, which is con- trolled from some central synchronous station. A cheap hy- draulic development, no regulation of waterwheel speed or gen- erator voltage, no attendance in the station beyond an occasional inspection, in short an automatically operating induction gen- erator station controlled from the central receiving station. In many cases, we can not anticipate what application an unused type of apparatus may find, and when its use may be economically demanded, or we can only in general realize, that with the increasing use of electric power, and with the intro- duction of electricity as the general energy supply of modern civilization, the operating requirements will become more diver- sified, and where today one single type of machine suffices — as the squirrel-cage induction motor — various modifications thereof 474 ELECTRICAL APPARATUS will become necessary, to suit the conditions of service, such :,s the double squirrel-cage induction' motor in ship propulsion sad similar uses, the various types of concatenation of induction machines with synchronous and commutating machines, etc 256. In general, a new design or new type of machine or apparatus has economically no right of existence, if it. is only jnst aa good as the existing one. A new type, which offers only a slight advantage in efficiency, size, coat of production or operation, etc., over the existing type, is economically preferable only, if it can entirely supersede tfw existing type; but if its advantage is limited to certain applica- tions, very often, even usually, the new type is economically inferior, since the disadvantage of producing and operating two different types of apparatus may !»■ greater than the advantage of i he new type. Tims a standard type is economically superior ami preferable to a special one, even if the latter has some small superiority, unless, and until, the industry lias extended so far, that both types can find such extensive application as in ju:-tif>- the existence of two standard types. This, for instance, was the reason which retarded the introduction of the three-phase trans- former: its advantage was not sufficient to justify the dupli- cation of standards, until three-phase systems had bet <■ my numerous and widespread, In other words, the advantage offered by a new type of appara- tus over existing standard types, must be very material, to economically justify its industrial development. The error most frequently made in modern engineering is m>t the undue adherence to standards, but is the reverse. The undue preference of special apparatus, sizes, methods, eic. where standards would be almost a3 good in their characteristics, and therefore would be economically preferable. It is the most serious economic mistake, to use anything special, when' standard can l>e made to serve satisfactorily, and this mistake i> the BitxA frequent in modern electrical engineering, due In the innate. individualism of the engineers. 267. However, while existing standard types of apparatus are economically preferable wherever they can be used, it is ohvious that with the rapid expansion of the industry, new types of apparatus will be developed, introduced and become standard, to meet new conditions, and for this reason, aa Btated above, I knowledge of the entire known field of apparatus is to the engineer. CONCLUSION 475 Most of the less-known and less-used types of apparatus have been discussed in the preceding, and a comprehensive list of them is given in Chapter XXIII, together with their definitions and short characterization. While electric machines are generally divided into induction machines, synchronous machines and commutating machines, this classification becomes difficult in considering all known apparatus, as many of them fall in two or even all three classes, or are intermediate, or their inclusion in one class depends on the particular definition of this class. Induction machines consist of a magnetic circuit inductively related, that is, interlinked with two sets of electric circuits, which are movable with regards to each other. They thus differ from transformers or in general stationary induction apparatus, in that the electric circuits of the latter are stationary with regards to each other and to the magnetic circuit. In the induction machines, the mechanical work thus is pro- duced— or consumed, in generators — by a disappearance or appearance of electrical energy in the transformation between the two sets of electric circuits, which are movable with regards to each other, and of which one may be called the primary cir- cuit, the other the secondary circuit. The magnetic field of the induction machine inherently must be an alternating field (usually a polyphase rotating field) excited by alternating currents. Synchronous machines are machines in which the frequency of rotation has a fixed and rigid relation to the frequency of the supply voltage. Usually the frequency of rotation is the same as the frequency of the. supply voltage: in the standard synchronous machine, with direct-current field excitation. The two frequencies, however, may be different: in the double synchronous generator, the frequency of rotation is twice the frequency of alternation; in the synchronous-induction machine, it is a definite percentage thereof; so also it is in the induction machine concatenated to a synchronous machine, etc. Commutating machines are machines having a distributed armature winding connected to a segmental commutator. They may be direct-current or alternating-current machines. Unipolar machines are machines in which the induction is produced by the constant rotation of the conductor through a constant and continuous magnetic field. 476 ELECTRICAL APPARATUS The list of machine types and their definitions, given in Chapter XXIII, shows numerous instances of machines belong- ing into several classes. The most common of these double types is the converter, or synchronous commutating machine. Numerous also are the machines which combine induction- machine and synchronous-machine characteristics, as the double synchronous generator, the synchronous-induction motor and generator, etc. * The synchronous-induction machine comprising a polyphase stator and polyphase rotor connected in parallel with the stator through a commutator, is an induction machine, as stator and rotor are inductively related through one alternating magnetic circuit; it is a synchronous machine, as its frequency is definitely fixed by the speed (and ratio of turns of stator and rotor), and it also is a commutating machine. Thus it is an illustration of the impossibility of a rigid classi- fication of all the machine types. INDEX Also see alphabetical list of apparatus in Chapter XXIII. Acyclic, see Unipolar. Adjustable speed polyphase motor, 321, 378 Alcxanderson very high frequency inductor alternator, 279 Amplifier, 281 Arc rectifier, 248 Armature reaction of regulating pole converter, 426, 437 of unipolar machine, 457 B Balancer, phase, 228 Battery charging rectifier, 244 Brush arc machine as quarterphase rectifier, 244, 254 Capacity storing energy in phase conversion, 212 Cascade control, see Concatenation. Coil distribution giving harmonic torque in induction motor, 151 Commutating e.m.f. in rectifier, 239 field, singlephase commutator motor, 355, 359 machine, concatenation with in- duction motor, 55, 78 pole machine, 472 poles, singlephase commutator motor, 358 Commutation current, repulsion motor, 392 series repulsion motor, 400, 404 factor, repulsion motor, 392 Commutation factor of series repul- sion motor, 415 of regulating pole converter, 426, 437 of series repulsion motor, 403 of singlephase commutator motor, 347 Commutator excitation of induction motor, 54, 89 induction generator, 200 leads, singlephase commutator motor, 351 motors, singlephase, 331 Compensated series motor, 372 Compensating winding, singlephase commutator motor, 336, 338 Concatenation of induction motors, 14, 40 Condenser excitation of induction motor secondary, 55, 84 singlephase induction motor, 120 speed control of induction motor, 13, 16 Contact making rectifier, 245 Cumulative oscillation of synchro- nous machine, 299 D Deep bar rotor of induction motor, 11 Delta connected roctifier, 251 Direct current in induction motor secondary, 54, 57 Disc type of unipolar machine, 454 Double squirrel cage induction motor, 29 Double synchronous induction gen- erator, 191, 199, 201 Drum type of unipolar machine, 454 477 478 lUfiEX E Eddy current starting device of in- duction motor, 8 in unipolar machine, 456 Eickemeyer high frequency inductor alternator, 280 F Flashing of rectifier, 249 Frequency converter, 176 pulsation, effect in induction motor, 131 Full wave rectifier, 245 G General alternating current motor, 300 Generator regulation affecting induc- tion motor stability, 137 H Half wave rectifier, 245 Harmonic torque of induction motor, 144 Heyland motor, 92 Higher harmonic torques in induc- tion motor, 144 Homopolar, see Unipolar. Hunt motor, 49 Hunting, see Surging. Hysteresis generator, 169 motor, 168 starting device of induction motor, 5 I Independent phase rectifier, 251 Inductance storing energy in phase conversion, 212 Inductive compensation of single- phase commutator motor, 343 devices starting singlephase in- duction motor, 97, 111 Inductive excitation of singlephase commutator motor, 343 •Induction frequency converter, 191 generator, 473 motor inductor frequency con- verter, 284 phase balancer stationary, 228 phase converter, 220 Inductor machines, 274 Interlocking pole type of machine, 286 Internally concatenated induction motor, 41, 49 Lead of current produced by lagging field of singlephase com- mutator motor, 366 Leblanc's rectifier, 256 Load and stability of induction motor, 132 Low frequency exciter of induction generator, 199, 203 M Magneto commutation, 285 inductor machine, 285 Mechanical starting of singlephase induction motor, 96 Mercury arc rectifier, 247 Meter, unipolar, 458 Momentum storing energy in phase conversion, 212 Monocyclic devices, 214 starting singlephase induction motor, 98, 117 Motor converter, 192 Multiple speed induction motor, 14, 20 Multiple squirrel cage induction motor, 11, 27 O Open circuit rectifier, 237 Over compensation, singlephase com- mutator motor, 418 .«' INDEX 479 Permutator, 257 Phase balancer, 228 control by polyphase shunt motor, 324 by commutating machine with lagging field flux, 370 conversion, 212 converter starting singlephase induction motor, 98 splitting devices starting single- phase induction motor, 97, 103 Polyphase excitation of inductor alternator, 283 induction motor, 307 rectifier, 250 series motor, 327 shunt motor, 319 Position angle of brushes affecting converter ratio, 422 Power factor compensation by com- mutator motor, 379 of frequency converter, 178, 184 Pyroelectric speed control of induc- tion motor, 14 Q Quart erphase rectifier, 251 R Reaction converter, 264 machine, 260 Rectifier, synchronous, 234 Regulating pole converter, 422 Regulation coefficient of system and induction motor stability, 140 of induction motor, 123 Regulator, voltage-, magneto com- mutation, 285 Repulsion motor, 343, 373, 385 starting of singlephase induc- tion motor, 97 Resistance speed control of induc- tion motor, 12 Reversing rectifier, 245 Ring connected rectifier, 251 Rotary terminal singlephase induc- tion motor, 172 S Secondary excitation of induction * motor, 52 Self induction of commutation, 420 Semi -inductor type of machine, 286 Series repulsion motor, 343, 374, 397 Shading coil starting device, 112 Short circuit rectifier, 237 Shunt resistance of rectifier, 235 and series motor starting of singlephase induction motor, 96 Singlephase commutator motor, 331 generation, 212, 229 induction motor, 93, 314 self starting by rotary ter- minals, 172 Six-phase rectifier, 253 regulating pole converter, 446 Split pole converter, see Regulating pole converter. Square, monocycle, 216 Stability coefficient of induction motor, 138 of system containing induc- tion motor, 141 Stability of induction motor and generator regulation, 137 limit of rectifier, 249 and load of induction motor, 132 Stanley inductor alternator, 275 Star connected rectifier, 251 Surging of synchronous machine, 288 Synchronizing induction motor on common rheostat, 159 Synchronous exciter of induction motor, 72 frequency converter, 191 induction generator, 191, 194 induction generator with low frequency exciter, 199, 203 induction motor, 166 as reaction machine, 264 480 INDEX Synchronous machines, surging, 288 motor, concatenation with in- duction motor, 54, 71 phase balancer, 228 phase converter, 227 rectifier, 234 U Unipolar induction, 452 machines, 400 motor meter, 458 Tandem control, see Concatenation. Temperature starting device of induction motor, 2 Third harmonic wave controlling converter ratio, 432 Thomson-Houston arc machine as three-phase rectifier, 244, 255 Three-phase rectifier, 251 regulating pole converter, 445 transformer, 472 Transformer, general alternating, 176 Triangle, monocyclic, 216 Triple squirrel cage induction motor, 34 Variable ratio converter, see Regu- lating pole converter. W Wave shape affecting converter ratio, 430 harmonics giving induction motor torque, 145 Winter-Eichbcrg motor, 380 V connected rectifier, 251 t • ■■^^ THE NEW RBP ] Thia book b tak YORK PUBLIC LIBRARY BRENCB DEPARTMENT under no circumstance* lo be en from the Build inf | '-'"•'■