Design Principles of a New Generator Stator Ground Relay for 100% Coverage of the Stator Winding

The design principles of a new relay for detection of grounds on the stator windings of generators is discussed. The relay provides 100% coverage of the stator windings with measurement of the fundamental and third harmonic components of the residual voltage at the terminals of the generator and the voltage across the grounding resistor at the neutral of the generator. The design concepts of the detectors utilizing the third harmonic components of the above signals are based on measurements of these signals on a number of Ontario Hydro thermal units.