接地故障零序方向元件拒动保护改进方案

对于大电源长线路的输电系统,当线路末端发生接地故障时,虽然零序电流达到定值,零(负)序方向元件由于零(负)序电压可能达不到方向元件的门槛值,造成保护拒动.针对这类问题,提出了2种解决方案:一种是当零(负)序方向元件由于零(负)序电压可能达不到方向元件的门槛时,以正序电压代替零(负)序电压作为零序电流方向判别;另一种是采用无方向零序电流反时限过流保护作为接地故障后备保护,并提出了新的电流互感器断线方案,解决了国内保护装置电流互感器断线与反时限零序后备存在的矛盾.

Improvement on Zero Sequence Current Protection When Directional Element Fails to Operate During Earth Faults

When earth faults occur at the end of long power lines in strong source networks, traditional zero sequence (negative sequence) directional element may not operate due to very low zero sequence (negative sequence) voltage which is lower than the threshold of the directional element, although zero sequence current reaches the set value of protection relay. Two kinds of solution to this problem are proposed: One is that using positive sequence voltage instead, when zero sequence (negative sequence) voltage is lower than the threshold of the directional element, the other is that using non-directional zero sequence current protection with inverse time characteristic as a backup protection and applying new principle of current transformer circuit supervision.