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

Single phase earth-fault in MV grids usually causes overvoltagethat harm to human being and electric equipments. In 6kV mining grids ofVietnam, earth fault which is majority incident accounts 55% to 73% of thetotal faults. When earth fault occurs many grids’ eco-technical parameterswill be affected. Moreover, the overvoltage and earthing current can lead toserious electric shock accidents caused mainly by stepping-overvoltage ortouching-overvoltage. One of earthing relays requirements is to trip inminimum time duration in order to reduce the magnitude of earthing currentsand overvoltage. Base on the simulation in Matlab, the paper suggests a priorconnection diagram that allows an auto earthing-connection for improvingthe better performance of relays. The utilization of the diagram will help todecrease the tripping time of relays, reduce the amplitude of internalovervoltage as well as enhance the safety for human being in case ofearthing incidents.