Abstract: With the continuous promotion and application of new power systems, phase selector for phase to phase current sudden change,steady-state zero negative sequence current, and weak feedback in high-voltage line backup protection are all affected to varying degrees. Especially when a two-phase short circuit grounding occurs at the reverse exit of the line, the voltage value of the non-fault phase is relatively small. The protection may mistakenly select a three-phase fault, resulting in the misoperation of the phase-to-phase distance zone III protection.Thus, a phase selection method combining voltage sequence components with measuring impedance has been proposed. Compared with the original current sequence component phase selection method, the performance of this phase selection method has been significantly improved and it has a better phase selection effect. It can solve the problem of misoperation of phase-to-phase distance zone III protection when the two-phase short-circuit grounding at the reverse direction outlet occurs.

    Key words: new power system; phase selector; voltage sequence component; measure impedance; misoperation