Third harmonic differential over current relay based protection system for stator ground fault in synchronous generator

Abstract

In this paper, a new method is proposed for 100% protection against the stator earth fault in synchronous generator. Conventional ground fault protection schemes can be applied to any generator but it covers at most 95% of generator stator length. For ensuring 100% protection of synchronous generator stator winding, conventional ground fault schemes are combined with our proposed third harmonic differential over current protection scheme. Moreover, an investigation into the differences between first harmonic fault current and third harmonic fault current is performed. By using proper simulation model, earth faults are simulated at various distant points from the generator neutral and using this simulations, first harmonic fault current and third harmonic fault current characteristics are properly distinguished. Finally, the threshold current of our proposed differential third harmonic over current relay is selected based on the results of the simulations.