一起主变零序CT开路引发的公用变比率差动保护误动分析

The maloperation of common variable ratio differential protection caused by the main transformer zero sequence CT disconnection

介绍了一起因电厂侧主变压器零序电流互感器(CT)存在开路点,当电网侧区外发生单相接地故障时,导致公用变压器比率差动保护误动的事故。揭示了当零序CT二次侧存在开路点时,感应出的二次高电压有可能对相邻交流采样回路产生影响,并分析了这种现象的典型波形特征,提出了针对性的防范措施,供分析此类不明原因的故障时参考。

It analyzes an accident due to the disconnected point of zero-sequence CT circuit of a main transformer on the power plant side. When a single-phase ground fault occurs outside the grid side zone,it leads to a utility variable ratio differential protection. It reveals that if there is disconnected point in a zero-sequence CT secondary side,the induced secondary high voltage may affect the adjacent AC sampling loop. Analyzing the typical wave characters of this accident,specific preventive measures are put forward as references for the unknown accident.