Stator Winding Grounding Fault Protection with Third Harmonic Current Difference for Multi-Generator Systems

Most small or medium waterpower generation stations are multi-generator-systems (MGS) with more than one generator directly connecting a bus. A novel selectivity protection for generator stator grounding faults in the MGS is proposed in the paper. The third harmonic currents of each phase are measured in generator neutral points and generator terminals respectively. The third harmonic leaking current differences between phases from the stator to earth are calculated. The fault phase and the ground fault generator with the current difference larger than its threshold are thus detected, and the selectivity protection scheme is also presented. Theory analysis and EMTP simulation results show that the protection can detect the ground fault generator with selectivity, it can detect the faults on or near the generator neutral point and the generator terminal with high precision.