High-Speed Magnetic Air Circuit Breaker for Distribution Circuits

Field tests indicate that very fast clearing of faults on 4-kv open-wire distribution circuits will materially reduce wire burndowns and consequently improve the service interruption record. Heretofore, the fastest air circuit breakers available for this service, exclusive of compressed-air breakers, have interrupting times of 3¿ to 5¿ cycles. A magnetic-type air breaker with 1¿ to 2 cycles interrupting time is now available; see Fig. 1. These interrupting times approach those of line reclosers which have proved extremely satisfactory in preventing burndown of overhead distribution conductors.