抑制变压器中性点直流电流的措施研究

为了抑制在直流输电系统单极大地回线运行方式下换流站接地极附近的中性点接地变压器上产生的直流分量，分别对3种抑制措施进行了研究：中性点串联电阻接地、交流输电线串联电容和中性点串联电容接地。结合岭澳和大亚湾核电站主变的具体情况，按实测的流过主变中性点直流电流结果建立了相应的大地电网计算模型，并对在变压器中性点串联电容的方法进行了深入的分析，还根据分析结果提出了有关设备的主要技术参数。研究结果表明：抑制流入变压器中性点直流电流的最优方法是在变压器中性点串联电容。

STUDYING ON MEASURES OF RESTRAINING DC CURRENT THROUGH TRANSFORMER NEUTRALS

The DC current through transformer neutrals may make the transformers DC biases. There are three main measures to restrain DC current through transformer neutrals which are connected to ground near the converter station of HVDC transmission system when the HVDC transmission system operates in ground return mode. They are (1)putting a resistor in series between transformer neutral and ground, (2)putting a capacitor in series on AC transmission line and (3)putting a capacitor in series between transformer neutral and ground. Combining with the real instance of the transformers at Lingao and Dayawan nuclear power stations, these three measures are studied by building a module of power system with ground grid according to the DC current values measured at the transformer neutrals of Lingao and Dayawan nuclear power stations. The measure of putting a capacitor in series between transformer neutral and ground is studied further. Some main technology parameters are put forward according to the results of study. The results of study show that the optimum measure to restrain DC current through transformer neutrals at Lingao and Dayawan nuclear power stations is to put a capacitor in series between transformer neutral and ground.