接地故障电流入侵差动保护导致其误动作的实例分析

摘要

The transformer differential protection of the No. 3 transformer in substation incorrectly operated when the external single-phase fault occurred on 220 kV power line. The inspection found that the secondary side of the C-phase CT 35 kV side of the transformer phase-to-ground insulation damaged, which caused the two-point earthed faults. The earth current caused the changing of ground potential of substation when the single phase fault occurred on power line, which resulted in voltage △ U between the two-point earthed. The voltage ∆U produced an additive current ∆I, the value of which exceeded the protection settings, resulting in the malfunction of transformer differential protection. The problem has been solved by taking measures to control the value of the ground potential.%变电站220 kV 线路发生单相接地短路时，其主变压器差动保护动作跳闸，在现场发现变压器35 kV 侧 CT 二次回路 C相对地绝缘击穿，造成了二次两点接地。分析认为，差动保护的动作是地电流起动的。当高压线路上发生单相或两相接地故障时短路电流进入大地，是地电流的作用导致变电站地电位的不等，在两个接地点之间产生了电位差∆U，由此在保护的输入通道附加了一个地电流∆I，并且电流超过了保护的整定值，造成了保护的不正确动作。采取了控制地电位的升高等措施以后效果良好，再未出现类似的问题。