In recent years, shutdown accidents caused by thyristor voltage monitoring (TVM) board failure have occurred several times in converter stations. With the increase of operation time, the working reliability problem of TVM board becomes a challenge to the safe operation. This paper studies the effects of pollution severity and relative humidity (RH) on the function of TVM board. The results show that the increase of RH can lead to the advance or even disappearance of check-back signals. Furthermore, the increase of pollution severity can decrease the failure RH threshold. Through simulation and equivalent experiment, it is verified that the resistance decrease of the voltage balancing resistor under the combined effect of contamination and RH is the main reason for the advance of check-back signals. According to the experiments, it is found that the upper surface contamination has a greater effect on the function of TVM board than the lower surface contamination, resulting in more decrease of the failure RH threshold. In addition, leakage current at different RH is also measured. Results show that the pulse peak of leakage current is closely related to check-back signals. When the pulse peak is too small or disappears, check-back signals also disappear, indicating that the TVM board fails.

中文翻译：

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污染和相对湿度对晶闸管电压监测板功能的影响

近年来，换流站多次发生因晶闸管电压监测（TVM）板故障引起的停堆事故。随着运行时间的增加，TVM板的工作可靠性问题成为对安全运行的挑战。本文研究了污染严重程度和相对湿度 ( RH ) 对 TVM 板功能的影响。结果表明，RH的增加会导致回测信号的提前甚至消失。此外，污染严重程度的增加可以降低故障RH阈值。通过仿真和等效实验验证了电压平衡电阻在污染和RH共同作用下的阻值下降是check-back信号提前的主要原因。根据实验发现，上表面污染比下表面污染对TVM板功能的影响更大，导致故障RH阈值降低更多。此外，还测量了不同RH下的漏电流。结果表明，漏电流的脉冲峰值与反馈信号密切相关。当脉冲峰值过小或消失时，回测信号也消失，表明TVM板出现故障。