Neutral-Grounding Resistors (NGRs) are used to ground power
systems by inserting a resistor between the system neutral and
ground. This lowers the prospective ground-fault current to a
predetermined value.
A properly designed resistance-grounded system provides benefits
over both ungrounded and solidly grounded systems. Because the
system is grounded, transient overvoltages do not occur and groundfault
current can flow, allowing it to be detected and measured. Also,
because a resistor is used to ground the system, the very large and
destructive ground-fault currents of solidly grounded systems are
absent. Ground-fault relays (such as the SE-701) can be used on
feeders to provide selective coordination and the ability to quickly
locate or isolate the fault.