Study of a fresh subharmonic injection scheme based on equilibrium principle for hydro-generator stator ground protection

Based on conventional subharmonic injection scheme for hydro-generator stator ground protection, a new subharmonic injection scheme based on the equilibrium principle is proposed. The protection criterion of the scheme, i.e. the ground fault resistance, is achieved only by current measurements and is not affected by the internal resistance of injected voltage source. The scheme is characterized with the applicability for digital protection because of the reliability and simplicity of computation. Simulation test results show that the scheme operates properly not only during a solid ground fault, but also during intermittent arc ground fault. Therefore the scheme possesses comparatively high practical value.