高压厂变有载合闸时的差动保护误动作分析

Analysis on Mal-operation of Differential Protection of High-voltage Auxiliary Transformer During On-load Switch-in

分析了一起厂用负荷由起备变低压侧切到高压厂变低压侧时,高压厂变差动保护误动的案例,结果表明由于起备变和高压厂变低压侧电压之间相位差较大,导致切换过程中产生了有载合闸励磁涌流,衰减直流分量使电流互感器局部暂态饱和,两侧校正电流出现了较大的相位偏差,从而产生了差动电流,导致比率差动保护动作。为了防止再发生类似事故,可采取提高厂变比率差动保护启动定值或二次谐波综合制动等技术措施。

This paper introduces a case of mal-operation of auxiliary transformer differential protection during the auxiliary load is switched from low voltage side of standby transformer to that of auxiliary transformer.The analysis results show that the phase difference between low voltage side of standby transformer and low voltage side of auxiliary transformer causes excitation surge current during the switching.The partial transient saturation of the current transformer due to the slowly attenuated direct component of the surge current and significant phase difference of correcting current at both sides that causes differential current are main reasons of mal-operation of differential operation.In order to prevent the next reoccurrence of similar accidents,measures such as elevation of ratio differential starting value and comprehensive harmonic restraint mode may be taken.