直流输电系统偏磁抑制措施引起的过电压研究

Research on Over-voltage Caused by Magnetic Bias Suppressing Measures in DC Transmission System

高压直流输电系统采用单极—大地回路运行方式时,巨大的入地电流会使接地极附近的变电站主变产生直流偏磁,影响主变及交流系统的安全稳定运行。电阻限流法和电容隔直法已成为抑制直流偏磁的有效方法,但会抬升主变中性点过电压水平,对绝缘造成威胁。在采用电阻限流法和电容隔直法后,对220 kV与500 kV典型变电站的主变中性点短路过电压及雷电过电压进行了计算分析,对中性点绝缘水平进行了校核,并从绝缘水平的角度对电阻限流法的电阻取值提出了建议。

When HVDC transmission system works in monopole-ground circuit mode,enormous DC current into earth leads to the DC magnetic bias in the transformers nearby the grounding pole,which affects the safe and stable operation of transformer and AC system.The resistor current limiting and capacitor DC isolation methods have become effective ways of DC Bias inhibition,but will raise the over-voltage level of transformer neutral point and cause harm to the insulation.This paper calculates and analyzes the short circuit over-voltage and lightning impulse over-voltage of transformer neutral point in typical 220 kV and 500 kV substation,checks the insulation level of transformer neutral point,and provides suggestion on resistance value with regard to insulation level when resistor current limiting method is adopted.