Protection of large D-C machines by means of high-speed circuit breakers

R. C. Dickinson (Westinghouse Electric and Manufacturing Company, East Pittsburgh, Pa.): It appears that the authors have done a good job in remedying an unhappy situation by means of high-speed breakers. However, the general value of this development to the industry is somewhat doubtful, since the generation of large amounts of d-c power is now quite generally accomplished with rectifiers instead of rotating machines. The performance of this breaker appears to compare favorably with other devices, which have been in production for more than 12 years. As shown by the authors´ bibliography the value of high-speed breakers in limiting high d-c short circuits to less than the ultimate current has been known for a good many years, and devices of this type have been applied in continuous ratings up to 3,000 amperes for more than 20 years. It thus would seem unnecessary to use such high figures as 450,000 amperes from “a 300-volt 3,000-kw generator” and 700,000 amperes on an unstated number of machines presumably at 650 volts. There is no doubt that, although ultimate short-circuit currents in heavy d-c installations can be quite high, actual circuit and short-circuit resistances do not permit the extreme values given by the authors.