Single-phase fault detecting circuit breaker

Abstract

An electronic control system and associated circuit breaker is taught in which the effect of in-rush current on mining equipment, for example, in regard to tripping is minimized even though a single phase fault of an equal magnitude is adequately provided for. This is done even though the same circuit breaker system and circuit breaker for both situations is utilized. A resistive capacitive series network is utilized to separate the ripple frequency from the DC value of the overload current being sensed. If the ripple component is relatively high for a given amount of overload current in the lines to be protected, then that is indicative of a single-phase fault for which circuit breaker tripping should be provided. If on the other hand the same amount of current causes a ripple component of a relatively low value, that is indicative of balanced three-phased overload which is usually indicative of in-rush or spurious transients. In any case, higher values of overload will cause other portions of the circuit to trip for safety. A time delay is provided at the output of an operational amplifier interconnected with the series resistive capacitive circuit. The time delay provides further protection against spurious tripping. Furthermore, tuned feedback is provided for the operational amplifier to distinguish between the ripple frequency of a single-phase fault and the ripple frequency of a three-phase fault.