METHOD FOR BLOCKING OPERATION OF OVERCURRENT RELAY FOR EARTH FAULT,

摘要

A method for blocking operation of an overcurrent relay for earth fault comprises generating a fault signal from a three-phase overcurrent element and a ground fault element of the overcurrent relay, after sensing the fault current from any faulty phase and ground of transmission lines. The fault signal is transmitted from the three-phase overcurrent element and the ground fault element of the overcurrent relay to a combinational logic circuit. Checking is made whether the fault signal lies in line to ground fault, line to line to ground fault, line to line fault and three phase fault by using the combinational logic circuit. The trip operation of the overcurrent relay is blocked or allowed in response to preset tripping conditions obtained by checking the fault signal. Such method allows sensitive current and time setting for the overcurrent relay within the requirement of Critical Clearing Time (CCT), avoids nuisance tripping for system ground fault and also enhances the reliability of electric power supply. Fig 1[IN-MUM-2008-01476A]