Applying 100% stator ground fault protection by low frequency injection for generators

This paper covers practical considerations for proper application of this protection for a variety of different applications. The total capacitance to ground of the generator stator windings, bus work and delta-connected transformer windings of the unit transformer is a very important factor and must be known to ensure the protection settings are correctly determined. It will be shown that unless special steps are taken in the design of this protection, there are cases when it is hard to distinguish between normal operating conditions and an actual ground fault. The protection must also reject fundamental frequency (50 or 60 Hz) voltage and current signals that are present during ground faults on the stator windings. A real-life example for a back-to-back start at a pump storage facility, captured via relay oscillography, is included.