复杂土壤结构对流入变压器直流电流的影响分析

Analysis of the Influence of Complex Soil Structure on DC Current Flowing into Transformer

直流输电系统以单极大地方式运行时,地中流散的直流电流流入极址附近交流变压器中性点,导致变压器产生直流偏磁现象。研究土壤结构对流入变压器的直流电流的影响是分析变压器直流偏磁现象的基础。建立考虑山川、海洋、湖泊等复杂土壤结构的直流接地极特性电磁场有限元模型,计算直流接地极散流产生的地中电位;结合变电站电路模型计算流入相应变压器的直流电流;在此模型基础上分析极址附近交流变电站接地网位置对流入变压器直流电流的影响。结果表明:当两交流变电站之间连线与山川、海洋平行时,流入变压器的直流电流量最小;两变电站位于山川远离接地极的一侧时,由于高电阻率山川的电流阻碍作用,流入变压器的直流电流较均匀土壤情况有明显降低;两变电站位于湖泊两侧时,由于湖水的良导电作用,两侧变电站电位差及流入变压器的直流电流较均匀土壤情况下明显降低。

When the HVDC transmission system operates in a single maximal mode,the DC current flowing in the ground flows into the neutral point of the AC transformer near the pole site,causing the transformer to generate DC bias.Studying the influence of soil structure on the DC current flowing into the transformer is the basis for analyzing the DC bias phenomenon of the transformer.In this paper,the electromagnetic field finite element model of DC grounding characteristics is established considering complex soil structures such as mountains,oceans and lakes,and the ground potential generated by DC grounding strip current is calculated.The DC current flowing into the corresponding transformer is calculated by the substation circuit model.The influence of the position of the grounding grid of the AC substation near the pole site on the DC current flowing into the transformer is analyzed.The results show that when the connection between the two AC substations is parallel to the mountains and the ocean,the amount of DC current flowing into the transformer is the smallest;when the two substations are located on the side of the mountain away from the grounding pole,the current flows into the transformer due to the high-resistance mountain current blocking effect.The DC current is significantly lower than that of the uniform soil.When the two substations are located on both sides of the lake,the potential difference between the two substations and the DC current flowing into the transformer are significantly lower than that of the uniform soil due to the good conductivity of the lake.