零、负序方向元件的特殊问题研究

Special problems in zero/negative sequence directional element

分析了交流电压回路在电压互感器(TV)回路两点接地﹑接地点不正确﹑接地点虚接,甚至于变电站接地网接地电阻过大等情况时,引起了零序电压相位的变化,进而引起零序方向保护误动的原因。分析了此种情况的负序方向元件的动作情况,并提出利用负序方向元件闭锁零序方向保护的方法来防止零序方向保护误动的解决措施,同时以一个现场故障实例说明了该方法的正确性。同时分析了当发生不对称接地故障,特别是经过高阻接地故障时由于零序﹑负序电压过小而引起零序方向元件﹑负序方向元件可能拒动的问题,并提出了利用对零、负序电压进行补偿的措施以提高零、负序方向元件的灵敏度。RTDS试验证明了该补偿措施的正确性。

The misoperations of zero sequence directional protection are analyzed,which are caused by the dual-point grounding of PT circuit,the improper or instable grounding,the extremely large grounding resistance of substation grounding network,etc.. It is the change of zero-sequence voltage phase that causes the misoperations. The behavior of negative-sequence directional element under such conditions is analyzed and it is proposed to use negative-sequence directional element to block zero-sequence directional protection,which is validated by a real field fault. For the operation failure of zero/negative-sequence directional element because of the extremely small zero/negative-sequence voltage,it is proposed to compensate the zero/negative-sequence voltage to increase its sensitivity, which is validated by RTDS experiment.