A magnetic-type air circuit breaker for 15,000-volt services

In the development of the five-kilovolt Magne-Blast air circuit breaker, it was shown that rapidly increased arc resistance was extremely effective in circuit interruption. This paper describes an extension of that principle in the development of a Magne-Blast circuit breaker for 15-kv services with an interrupting rating of 250,000 kva. The higher electrical resistance of the arc necessary for this voltage has been made possible by an increase in the thermal efficiency of the interleaving arc chute. The arc chute which provides this greater efficiency is discussed in some detail. The design of the breaker is described briefly as well as its application to metal-clad switchgear. Test data and representative oscillograms are submitted to substantiate the interrupting rating assigned to this breaker.