When phase to earth fault occurs on a neutral non-direct grounded power system, it is necessary to select the faulted circuit quickly,but so far this has not been done very well.

• 中性点非有效接地配电网发生单相接地故障时，尽快选出故障线路对电网运行有重要意义，但选线问题迄今尚未能很好解决。