Analysis of stator ground protection schemes for hydro-generator of Three-Gorges power plant based on zero sequence voltages

New mathematical models for the zero-sequence voltage of large hydro-generator on turn basis are used to study hydro-generator stator ground fault protection schemes in this paper. The evaluation and the comparison of the characteristics of some stator ground protection schemes are described by means of protection coverage-critical resistance curves. And the simulation results showed that those schemes would suffer low sensitivity when they are used to huge hydro-generators in Three-Gorges power plant. To overcome this disadvantage, new ground fault protection schemes with higher sensitivity based on fault components are developed in this paper.