Improving the operation of earth fault relays by auto earthing-connection at earth fault situations in 6kV mining grid of Quang Ninh

Single phase earth-fault in MV grids usually causes overvoltage that harm to human being and electric equipments. In 6kV mining grids of Vietnam, earth fault which is majority incident accounts 55% to 73% of the total faults. When earth fault occurs many grids’ eco-technical parameters will be affected. Moreover, the overvoltage and earthing current can lead to serious electric shock accidents caused mainly by stepping-overvoltage or touching-overvoltage. One of earthing relays requirements is to trip in minimum time duration in order to reduce the magnitude of earthing currents and overvoltage. Base on the simulation in Matlab, the paper suggests a prior connection diagram that allows an auto earthing-connection for improving the better performance of relays. The utilization of the diagram will help to decrease the tripping time of relays, reduce the amplitude of internal overvoltage as well as enhance the safety for human being in case of earthing incidents.