锦屏—苏南±800 kV特高压直流工程同里换流站在极1低端换流变压器充电试验期间，当换流变压器充电后无功控制系统发出滤波器投入命令，处于热备用状态的12组交流滤波器依次投入时，发生交流滤波器母线过电压保护跳闸，此后控制系统再次自动投入。经分析认定：用于无功控制的500 kV交流母线电压测量值低于交流系统低电压监视设定值，无功控制持续发出滤波器投入命令。通过增加低电压闭锁功能，避免了因测量回路故障引起的上述问题；同时，在交流滤波器控制程序中增加相应的联锁功能，以避免在滤波器退出放电未结束的情况下，滤波器再次投入。现场测试表明，程序的更改是正确、可靠的。

During the charging test on pole 1 lower-voltage converter transformer in Tongli Station of ±800 kV UHVDC project from Jinping to Sunan, when the reactive power control system gave a filter input command as converter transformer charging, twelve groups of AC filters in hot standby state were connected one by one. Then an over-voltage protection trip occurred at AC busbar, but the control system was automatically input again. The reason is that the voltage of 500 kV AC busbar used for reactive power control is less than the setting value of low voltage monitoring for Ac system (Umax), so the reactive power control continue gives a command to input filter. The above problems caused by measurement circuit fault are solved by adding the low-voltage limited function, and the interlock function is added in AC filter control program, in order to prohibit the AC filter connecting again when it is disconnected while its discharge is not finished. The tests on site prove the change of software is correct and reliable.