Monitoring neutral-grounding resistors

Many of the problems associated with ungrounded and solidly grounded distribution and utilization systems are overcome with resistance grounding. Resistance grounding limits point-of-fault damage, eliminates transient overvoltages, reduces the flash hazard and provides adequate tripping levels for selective ground-fault detection and coordination. High-resistance and low-resistance grounding systems are reviewed with respect to charging current, ground fault detection and ground fault coordination. Reasons for monitoring the neutral-grounding resistor (NGR) are presented. Problems associated with NGR monitoring are discussed and monitor design requirements are summarized. These design requirements guided development of a NGR monitor that measures current in the transformer neutral, transformer neutral-to-ground voltage and continuity of the NGR.