Generator Grounding

Standby and Emergency systems are often configured to provide 600 V or 480 V, 3-phase 4-wire service and are typically solidly grounded. In Solidly grounded systems the ground fault currents are very high and damaging and circuit protective devices have to operate to isolate the faulty circuit and interrupt the supply.

This even applies to the emergency or standby system such as a fire pump where the faulted circuit is tripped and the system de-energized with potentially disastrous consequences if there were no power during an emergency.

There is the option to isolate neutral loads and use high resistance grounding to protect the generator.

The latest thinking is to employ Hybrid Grounding which is a combination of the low- and high-impedance grounded systems. This hybrid system would effectively be low resistance for all external ground faults. If, however, the fault is a ground fault within the generator, the system would revert to a high-impedance grounded system and minimize the damage.