High Impedance Grounding Fault Protection for Low-resistance Grounding System Based on the Ratio of Phase Active Power Variation

The high impedance grounding fault of medium voltage distribution network is always a difficult and hot point in distribution network protection. Aiming at the problem that the traditional zero-sequence current protection is difficult to identify the faulty line due to the small short-circuit current when the single-phase grounding fault with high impedance occurs in the low-resistance grounding system, this paper studies the power frequency variation of the phase active power of the faulty line, and analyzes that the power frequency variation of the faulty phase active power is much larger than that of the nonfaulty phase, while the power frequency variation of the nonfaulty line is similar. Therefore, a distribution network protection scheme based on the power frequency variation of phase active power is proposed. This scheme constructs the three-phase ratio criterion of the power frequency variation of phase active power by using the difference of the power frequency variation of three-phase active power after the fault occurs. Finally, based on PSCAD/EMTDC simulation experiments, it is verified that the proposed algorithm can withstand the faulty resistance of 2000Ω in the low-resistance grounding system.