Device for detecting a fault in an AC supply

摘要

A device for detecting a fault in an AC supply comprises a circuit (CT, 100) for detecting a particular type of fault in an AC supply to a load (LD) and providing a corresponding output (10). A relay (RLA) is responsive to said output (10) to open a set of load contacts (SW1) in the AC supply to disconnect the load from the supply. Test means (TS, Rt, W2) are provided for simulating a supply fault of the said type, and means (C3, R5, SCR2, SOL, SW2) are provided for causing the load contacts (SW1) to open if they do not open in response to the simulated fault within a certain period of time.

主权项

1. A device for detecting a fault in an AC (Alternating Current) supply, comprising:
a detecting circuit comprising circuitry for detecting a differential current in the AC supply to a load, the differential current having a characteristic indicative of a type of supply fault to be detected, and providing a corresponding output, disconnect means comprising a first electromechanical switch controlling a set of load contacts, the first electromechanical switch being responsive to the corresponding output to open the set of load contacts to disconnect the load from the supply within a normal response time of the device, said normal response time being from about 40 ms to about 50 ms, test means for simulating a supply fault of the said type by causing the differential current, having the characteristic indicative of the said type of fault, to flow in the detecting circuit in the absence of the supply fault, and opening means for causing the load contacts to open within a certain period of time longer than the normal response time of the device, if they do not open in response to the simulated fault, the opening means comprising a charge storage device which is connected to the supply for charging up during periods when the differential current is caused to flow in the detecting circuit by the test means, the said certain period of time after which the load contacts are caused to open being the time taken for the voltage on the charge storage device to reach a predetermined level sufficient to cause a solid state switch to change state, the load contacts being caused to open in response to the change of state of the solid state switch.