乒乓式转子接地保护两点接地的误判和解决办法

Misjudge and its solution for pingpong type protection in two points ground fault

通过引进转子电流判据来避免乒乓式转子两点接地保护因为一点接地电阻在一点接地故障以后的突变而误动的情况。设正确动作和误判2种情况下保护装置算得的第2点接地电阻的大小相同,可以通过比较微机保护装置测得的两点接地故障和由于接地电阻突变导致误判的情况下从转子负端流出的转子电流的大小来确定是不是发生真正的两点接地故障,真的物理位置上的转子两点接地故障和假两点接地故障2种情况下从转子负端流出的转子电流大小是不一样的。可以利用这种区别来判断是发生了真的两点接地故障还是由于接地电阻的突变而造成的两点接地故障的误判,消除乒乓切换原理实现转子接地保护所固有的缺点。通过分析和验证发现,这种方法可以改进乒乓式转子接地保护的一些不足,实现更加可靠和完善的乒乓式转子接地保护。

The criteria of rotor current can avoid a wrong judgment for two points ground fault when the resistance of the one point ground fault changes. The two currents were compared, one was measured by protection device of a two points ground fault and the other was calculated by protection device when a wrong judgment happened. The rotor currents in a real two points ground fault and in a fake one are quite different. To use this difference can judge if a real two points ground fault happened or not. Depending on careful analysis and inspection, this solution can improve the pingpong type protection to be a better protection.