PROTECTION METHOD AND EQUIPMENT FOR EARTH LEAKAGE CURRENT SENSING CUIRCUIT OF RELAY

摘要

A protection method and equipment for earth leakage current sensing is provided to protect the fault current sensing circuit and prevent malfunction of the equipment. In a protection method and equipment for earth leakage current sensing, a current limit element and sensing resistor(3), having the impedance characteristic with non-linear to the internal heat generated between the zero current terminal in the motor protective relay, are connected in series. A processing unit(5) is controlled according to the output signal of the comparison voltage and reference voltage of the signal conditioner(4) which is obtained by the output of the sensing resistance. A current lime element connected to input terminal of the zero current is inserted into the secondary output circuit of the zero current transformer. A fuse connected to input terminal of the zero current in series is inserted into the secondary output circuit of the zero current transformer.