Starting currents of transformers : with special reference to transformers with silicon steel cores . Sll!Pll!AV / o> -uooag VAS 00 o o o S3 ?aO ooooooooo S M Tf« tN I » OOOOOOOOO o ooo to 5 tts N « O O nl - t t 0)N w « m M « 40 ILLINOIS K NO IN KICK INC LXIKUI M KNT STATION If each set of transformers be connected to one generator, theproblem will consist simply in bringing the voltage up slowly with thetransformers connected, but in cases where it becomes necessary toconnect transformers to busbars of full potential, it becomes necessary,for safe operation, to insert in the primary circui
Starting currents of transformers : with special reference to transformers with silicon steel cores . Sll!Pll!AV / o> -uooag VAS 00 o o o S3 ?aO ooooooooo S M Tf« tN I » OOOOOOOOO o ooo to 5 tts N « O O nl - t t 0)N w « m M « 40 ILLINOIS K NO IN KICK INC LXIKUI M KNT STATION If each set of transformers be connected to one generator, theproblem will consist simply in bringing the voltage up slowly with thetransformers connected, but in cases where it becomes necessary toconnect transformers to busbars of full potential, it becomes necessary,for safe operation, to insert in the primary circuit a resistance or in-ductance to limit the transient current to safe values. It has beenshown that a resistance or inductive reactance amounting to l/2 normal voltagefull load current will limit the current to less than twice full load current under themost critical conditions. This resistance or inductance needs to be in the circuit for onlya very short time, since the current will fall down to below full load. Transformer Fig. 17 current after a few cycles. The resistance or inductance may be con-nected as shown diagramatically in Fig. 17, where an extra contact, A,is provided on the switch, in such a way that, in closing the switch thecontact A is reached before the main contact B is reached. It mightbe possible to provide such a contact even on oil switches. As the in-terval between the time the switch touches A until it touches B, needbe only a fraction of one second, no change in the operating mechanismof the switch would be necessary. Usually, it takes an oil switch second to close, i. e., from the time it starts until the switch is the contact A is located 1/3 of the way from the closed position, itmay take the contact second to travel from A to B, and this timewill be sufficient even for 25 cycle systems. \ ENSEN —START I.\(, l IRUE NTS OF TRANSFORM ICRS 41 Appendix Residual Magnetism.—It has been generally believed that residualmagnetis
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