内桥接线主变压器差动保护误动原因分析

Analysis on Mal-operation of Differential Protection of Main Transformer with Internal Bridge Connection

内桥接线变电站的主变压器并列运行时,其中一台变压器支路空载合闸或故障时,内桥开关将通过很大的励磁涌流或短路电流。在此情况下,正常运行的变压器差动保护可能发生由于电流互感器暂态传变特性差异以及产生和应涌流现象而导致保护误动。文中结合一起变压器差动保护连续误动的事故,对内桥接线方式下,电流互感器传变特性差异、和应涌流的产生进行了理论分析和仿真验证,并对励磁涌流的二次谐波闭锁能力进行了分析计算。最后提出了内桥接线方式下改进的变压器差动保护接线方式等解决措施,以防止差动保护误动。

In the substation of internal bridge connection, the main transformer operates in parallel with another transformer. Huge inrush current or fault current will flow through bridge breaker when one of the main transformers switches on or fault occurs. In that case, the differential protection of normal operating transformer may mal-operate because of the transient characteristic differences of current transformers and sympathetic inrush current. Considering a case of continuous maloperations of differential protection, it is further analyzed and simulation validated on current transformer characteristic differences, phenomenon of sympathetic inrush current. Furthermore, it is calculated and analyzed on the ability of second harmonic to block the differential protection. Finally, the improved differential protection connection and some other measures are proposed to prevent differential protection from mal operation.