Fault detecting device for an electricity supply

摘要

A fault detecting device having a plurality of supply conductors, including a first current transformer having a primary winding comprising at least two supply conductors and a secondary winding into which a current is induced in response to a fault current in the primary winding. A fault detection circuit connects the secondary winding to an electromechanical actuator having mechanical contacts in the supply conductors, the fault detection circuit generating an output signal to the actuator when an induced current is detected in the secondary winding, the output signal causing the actuator to open the mechanical contacts. The device further includes a second current transformer having a primary winding connected to an oscillator and a secondary winding comprising at least one supply conductor, the second current transformer arranged to induce an oscillating current into the at least one supply conductor in the event of a fault condition.

主权项

1. A fault detecting device for an electricity supply having a plurality of supply conductors, the device including:
a first current transformer having a primary winding comprising at least two supply conductors and a secondary winding into which a current is induced in response to a fault current in the primary winding, and a fault detection circuit connecting the secondary winding to an electromechanical actuator having mechanical contacts in the supply conductors, the fault detection circuit generating an output signal to the actuator in response to the detection of an induced current in the secondary winding indicative of a fault current in the primary winding, the output signal causing the actuator to open the mechanical contacts, the device further including: a second current transformer having a primary winding connected to an oscillator and a secondary winding comprising at least one supply conductor, the second current transformer being arranged to induce an oscillating current into the at least one supply conductor in the event of a fault condition, and a test switch connected between a first point on one supply conductor upstream of the first and second current transformers and a second point on the same one supply conductor downstream of the first and second current transformers, wherein when the test switch is closed the oscillating current flows in a loop comprising the closed test switch and said one supply conductor to which the closed test switch is connected at said first and second points, the oscillating current being detectable by the first current transformer and fault detecting circuit as a fault current in the primary winding with consequent generation of an output signal from the fault detection circuit and opening of the mechanical contacts.