Abstract: Domestic power plant auxiliary power systems mostly use high-voltage auxiliary transformer low-voltage side grounding through medium resistance. When the feeder is grounded, it is moved by a fixed time-limit grounding protection to the hop fault feeder. But when the feeder is grounded with high resistance, the grounding current measured by the protection device will be small, which may resist the protection action. As a result, the factory power system sickly runs for a long term. If it’s not eliminated in time, the fault range may be expanded. It is proposed that on the basis of the original fixed time-limit protection, anti-time protection can be added for sending letters,which can quickly process fault feeders. The zero-sequence over current protection combined with fixed and anti-time limits can ensure that the fault feeder is positioned and alarmed according to the general anti-time limit curve when grounding is high. When the grounding resistance is small, it can quickly jump according to the fixed time limit. The zero-sequence one and second time-time export tuning methods of high-voltage plants contradict the functions of the factory power fast cutting device. This paper puts forward solutions to the problems above mentioned in order to ensure the safe operation of the factory power system.

    Key words: zero-sequence over current protection; rapid power cutting for factory use; high resistance grounding; capacitance current;zero-sequence current