小电流接地系统距离继电器动作行为分析

在小电流接地系统中不同地点发生两点接地故障时,采用两相星型接线方式的过电流保护在串联线路有2/3机会有选择性地切除后面一条线路,在并联线路有2/3机会有选择性地切除一条线路,而三相星型接线方式的过电流保护非选择性动作的几率比两相星型接线更大。如何提高小电流接地系统两点接地时保护动作的选择性一直是继保领域中的一个课题,论述了小电流接地系统串联线路及并联线路发生两点接地时,通过零序电流启动的接地距离保护与相间距离保护的动作行为及两者之间的配合,得出串联线路两点接地时,能100%地保证只切除后边的一条线路,而并联线路两点接地时,只切除一条线路的几率也很大。

Analyzing the operation of distance protection in non-solid earthed power systems

When two-point earthed faults occur in different spots of non-solid earthed power systems, overcurrent protection with two-phase Y connection mode will selectively cut off the next line with the chances of 2/3 in series circuit. And with the same chances, it will cut off a line selectively in parallel circuit. Moreover, the chances of non-selective operation for the protection with three-phase Y connection mode will be larger than that of two-phase one. To improve the selectivity of two-point earthed fault, the cooperation and operation mode between earthed and interphase distance protection enabled by zero-sequence current are described in series and parallel circuit respectively. The results verify the betterment of the line cutting in series(up to 100%) and parallel circuit.