Neutral ground resistor monitoring schemes

One distribution industrial/utility company in the Middle East has experienced several neutral ground resistor [NGR] failures during the past few years at its residential substations. These NGR´s are installed in the neutral of the distribution power system transformers to limit the ground fault current. The failure of these NGR´s caused the distribution system to be ungrounded. The existence of a phase to ground failure in the ungrounded power system leads to phase to ground voltage build-up in the other two healthy phases which can result in insulation breakdown and electrical equipment failures. This work is aimed at the development of two schemes and the evaluation of a third commercial existing scheme to detect NGR´s failures.