Ground fault protection circuit for a multiple source system

Abstract

An improved ground fault protection system is provided for protecting an electrical power distribution system having multiple sources and multiple grounds. In accordance with a preferred embodiment, an electrical power distribution circuit having a primary electrical circuit for distributing electrical power from a plurality of sources to a plurality of loads is provided with a ground fault protection circuit magnetically coupled to the primary circuit. The primary electrical circuit includes conventional main and tie buses for distributing power to the loads and switches or circuit breakers for interrupting power from flowing in the buses. The ground fault protection circuit includes current sensors, tripping functions or ground fault relays associated with each circuit breaker and a novel use of an auxiliary transformer. When a ground fault occurs, the ground fault protection circuit is capable of sensing and determining the specific bus in which a ground fault condition exists. It then selectively sends a trip current generated by the associated current sensor only to the proper tripping functions for tipping the appropriate circuit breakers in the affected bus in order to isolate the ground fault; this avoids unnecessary tripping of circuit breakers in bus portions which are not affected by the ground fault. The auxiliary transformer uniquely sends the trip current to portions of the ground fault protection circuits that would not have been connected, or accessible, in the ground fault protection circuits of the prior art.