Portable dc circuit breaker calibrator using high frequency thyristor converter

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 to be determined and subject the contacts to full current rating. The equipment is simple to use and weighs 93 lb. Connections are made with protected, clamp-on leads, which weigh about 21 lb. An accurate calibration procedure takes less than 5 minutes to complete.