1引言 　　随着配电网络的扩大，电缆线路增多，因此配电网络对地电容电流不断增加，致使单相接地时由于流过故障点的电容电流过大，使故障点的电弧不能自灭而发展到相间短路的机率增高；使电网的安全运行得不到保证。例如某 220kV变电站 10kV线路发生单相接地，使得主变跳闸， 1 Introduction With the expansion of distribution network and the increase of cable lines, the capacitance of the distribution network to the earth is constantly increasing. As a result, the arc current at the fault point can not be extinguished due to the excessive current flowing through the fault point during single-phase grounding. The probability of developing to short-circuit between phases increases; the safe operation of the power grid can not be guaranteed. For example, a 220kV substation 10kV line single-phase ground, making the main transformer trip,