scope:

This guide has been prepared to aid in the application of relays and relaying schemes for protection against stator ground faults on high-impedance grounded generators. The guide is not intended for the selection of generator or ground connection schemes.

Differential relaying will not detect stator ground faults on high-impedance grounded generators. The high impedance normally limits the fault current to levels considerably below the best practical sensitivity of the differential relaying. Separate ground fault protection is then provided.