. Traction électrique et ingénierie de la transmission . , 0.21 pi² par K.W..générateurs à induction, 0.31 pi² par K.W. L'emplacement séparé possible des convertisseurs et des transformateurs, par exemple la mise en place des transformateurs sur les sites d'alimentation, donne une flexibilité d'agencement des appareils notpossédés par les générateurs-moteurs. Avec le substationet urbain cher immobilier l'espace occupé de plancher devient un facteur important. Efficacité. — l'efficacité des convertisseurs synchrones est supérieure à celle des générateurs-moteurs. Même si aux elosses des convertisseurs être ajouté les pertes dans transformersand r
1557 x 1604 px | 26,4 x 27,2 cm | 10,4 x 10,7 inches | 150dpi
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. Electric traction and transmission engineering . , 0.21 sq. ft. per K.W.Induction motor-generators, 0.31 sq. ft. per K.W. The possible separate location of converters and trans-formers, for instance the placing of transformers on agallery, gives a flexibility of arrangement of apparatus notpossessed by motor-generators. With urban substationsand expensive real estate the occupied floor space becomesan important factor. Efficiency. — The efficiency of synchronous converters isgreater than that of motor-generators. Even if to thelosses of the converters be added the losses in transformersand regulating devices, which are not involved in the use ofmotor-generators, the efficiency of the combined converter SUBSTATIONS. 171 installation excels. W. R. C. Corson gives the averageoperating efficiencies from this point of view as follows: Synchronous converters 91% Synchronous motor-generators 85% Induction motor-generators 84% Figs. 72 and 73 contain curves showing the operatingcharacteristics of a shunt-wound, 25-cycle, 600-K. W. conver-. 0 25 50 75 100 125 150 175 200PER CENT, OF FULL LOAD CURRENTFROM COMMUTATORFig. 72. ter, and of a 50-cycle, 230-K.W. induction motor-generatorrespectively. ■ Regulation. — Since the ratio between the commutatorand slip-ring voltages of a converter is practically constant, irrespective of the field excitation, except in the case ofsplit-pole converters, it is customary to insert a reactancecoil in the circuit between the low-tension terminal of a 1/2 TRACTION AND TRANSMISSION. transformer and the converter slip ring which it supplieswith current, and to provide the converter with a seriesmagnetizing coil which is traversed by the direct currentfrom the commutator before it enters the feeders of thedistribution circuit. The field excitation is thereby causedto increase with load, and the alternating current whichenters the slip rings is therefore made to lead the impressedvoltage. The passage of the leading current through thereactan
