大型变压器中性点串接抑制直流电流电容后对继电保护影响分析

Analysis of DC Bias Suppression Method of the Large Transformer's Neutral Series Capacitor and Its Effect on Relay Protection

直流输电系统双极不对称或单极大地回线运行时产生的地电流会导致变压器直流偏磁,影响变压器及交流系统的安全稳定运行。以某500 k V变电站主变压器直流偏磁为例,在其变压器中性点加装电容设备以抑制直流偏磁,但这会改变主变压器的零序阻抗,对零序电流保护和接地距离保护造成影响。为了研究对这些保护造成的影响,进行了理论分析研究,并对理论分析的结果进行了仿真验证。结果表明,在主变压器中性点加装小阻值容抗不会对相应继电保护的性能造成影响。

HVDC power transmission system that works in monopole or bipolar asymmetric operation mode generates neutral current which causes transformer DC magnetic biasing and in turn influences safe and stable operation of transformer and AC systems.Taken a 500 kV substation as example,the capacitor connected in series to transformer neutral can suppress DC biasing.However,it also changes transformer zero sequence and behavior of zero-sequence current relay and distance relay.Theoretical analysis of relay protection is performed and analysis results are verified by simulation.The results show that small capacitor connected in series to the neutral point of station transformer has no influence on relay protection performance.