Modeling and analysis of generator rotor grounding protection based on combined principle

This paper analyzes several generator rotor grounding protecting methods and the existed problems. Theoretic analysis shows that the measurement accuracy of the first grounding resistance is very important for the calculation of the second point grounding resistance. In this paper, a new combined principle for generator rotor grounding is presented from the practical debugging and operating experience of generator-transformer protection. The new principle measures and calculates three times for the rotor grounding resistance and position combining the ping-pong method and the injected square-wave method. Theoretical analysis and the MATLAB simulation results based on the ALSTOM unit model of Three Gorges prove that the reliability and accuracy of the rotor one-point grounding protection is improved compared with conventional single measurement methods. The sampling circuit can also be monitored at the meantime.