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A portable calibrator to check the trip setting of direct current (dc)circuit breakers within an accuracy of ±5% has been developed and tested under Bureau of Mines Contract HO 122058. A prototype unit operates from a 300 Vdc trolley wire to provide controlled current pulses of 120 msec duration and continuously adjustable from 1,400 to 3,600 A. These current pulses enable a breaker dc trip current...
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