Research on new principle of pole discrepancy protection based on voltage phasor difference

The pole discrepancy fault of hydropower units and gas-turbine units may easily occur due to its frequent open and close operations. This cannot be detected by the traditional protection during the initial period of grid-connection and in the normal operation of grid-disconnection. This paper applies the symmetrical component method to analyze the voltage characteristics of both sides of breaking point in a single-machine infinite system. A PSCAD digital simulation model based on the parameters of NR (NR Electric Co., Ltd) dynamic simulation unit is established. The single-phase and dual-phase pole discrepancy faults are simulated to verify the correctness of theoretical calculation. Furthermore, a new principle of pole discrepancy protection based on the voltage phasor difference is proposed. The corresponding protection equipment is developed and the dynamic experiment is carried out on the NR dynamic simulation unit to verify the correctness of the new criterion. Independent of the current variable values and the three-phase discrepancy contact status, the new protection principle can availably detect the pole discrepancy fault during the initial period of grid-connection and normal operation of grid-disconnection for large-scale units.