Patent ID: 8964340
Filing Date: 2015-02-24
Classification: H02H

Abstract:
1. A device for detecting a fault in an AC supply, comprising a circuit for detecting a differential current in the AC supply to the load, said differential current having a characteristic indicative of a type of supply fault to be detected, and providing a corresponding output, said detecting circuit including a current transformer having the AC supply as primary windings and a secondary winding for detecting said differential current, means to disconnect the load from the supply if said output persists for at least a certain period of time, the disconnect means comprising an electromechanical switch comprising a coil controlling normally-closed contacts in the AC supply to the load, said normally-closed contacts referred to herein as load contacts, said electromechanical switch being responsive to said output subsisting for greater than said certain period of time to disconnect the load from the supply by opening the load contacts, and a generator of intermittent test pulses which are applied to a further primary winding of the current transformer, each test pulse having a duration less than said certain period of time and simulating a fault of the said type by causing a differential current, having a characteristic indicative of the said type of fault, to flow in the secondary winding in the absence of an actual supply fault of said type, said detecting circuit providing an output during each said test pulse, and means for providing a visual and/or audible indication in response to the detection of test pulses by the detecting circuit.