Stator winding ground fault protection with fault resistance measurement for multi-generator system

Most small or medium hydro-power generation stations are Multi-Generator-Systems (MGS) with more than one generator directly connected to a bus. A novel selectivity protection scheme for generator stator ground faults in the MGS is proposed in the paper. Three-phase currents are measured in generator neutral points and generator terminals respectively. The leaking current differences between phases, from stator to earth, are calculated. The characteristics of phase current changing caused by ground faults are analyzed. The fault resistance is calculated using the zero sequence voltage and the leakage current. The faulted generator is detected and located by comparing the resistance to its threshold value. Theoretical analysis and EMTP simulation results show that the protection system can detect the generator with the ground fault with selectivity. It can detect the faults on or near the generator terminal with high precision.