New solenoid mechanism for magne-blast breaker

The existence of relatively high electromagnetic forces in circuit breakers when subjected to fault currents of appreciable magnitude has long been recognized. One of the problems in the design of a circuit-breaker operating mechanism is to provide smooth and effective closing performance, even though the breaker be closed against a short circuit and is thereby subjected to these high electromagnetic retarding forces during the final portion of the closing stroke. The greater the magnitude of the short-circuit current, the higher these electromagnetic retarding forces become and the more serious the effects of any tendency to “stall” or, worse, to reverse momentarily the closing motion of the contacts. This paper describes a solenoid mechanism with novel design features developed to operate a new Magne-Blast circuit breaker of high interrupting rating and capable of closing that breaker against fault currents as high as 80,000 amperes rms.