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

Abstract

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.