一起主变差动保护误动实例分析及对策探讨

Analysis and Countermeasures on a Case of Mal-operation of Transformer Differential Protection

根据一台变压器空载合闸造成另一台并联运行变压器差动保护动作的故障录波数据,分析了运行变压器差动保护误动的原因。由于空载合闸变压器产生的励磁涌流引起桥侧电流互感器传变特性发生改变,从而使差动电流中的二次谐波含量降低,二次谐波闭锁保护失效,导致变压器差动保护误动。根据现场的实际情况和误动原因,探讨了如何防止励磁涌流引起的主变差动保护误动的对策。

A case of mal-operation of a transformer differential protection caused by another paralleled no-load transformer switching on is analyzed. The inrush currents caused by switching on of a no-load transformer result in the variation of current transformer＇ s transfer characteristics, which leads to a decline of the second harmonic in the differential current, so the second harmonic blocking scheme is invalid, resulting in mal-operation of the differential protection. Some countermeasures are proposed to prevent the differential protection from mal-operation by taking into account the field conditions.