The neutral grounding resistor is a current limiting electrical protection device connected between the neutral points of the generator and transformer. In case of failure in the power network, the neutral voltage will produce  an oset, especially in a grid system of cables whose capacitive earth current is high, arc grounding overvoltage  will be produced when the current is greater than the specied value so that the non-fault phase-to-ground  voltage will be greatly increased, the equipment insulation will be damaged, thus causing short circuit of  earthing at two or more points and power outage.