直流入地电流在交流电网中分布的研究

Research on the Distribution of DC Earth Current in AC Network

直流接地极的入地电流会在地下较大的范围内形成恒定电场,经中性点进入变压器内引起的直流偏磁将影响变压器正常运行。本文提出将包括变压器路的地上电路模型与包括接地电阻、变压器地电位的地下电磁场耦合起来,计算直流电流在交流电网中分布的方法,以某直流输电工程为例,研究变电站与直流接地极距离、土壤结构、主变台数和接地电阻、线路长度等参数对进入变压器直流电流的影响。结果表明:变电站与直流接地极距离越远,主变台数增加、接地电阻增大、线路电阻增加都能减小流入变压器的直流;深层土壤结构对地电位分布影响显著,深层土壤电阻率越大,引起直流接地极附近的电位升越大,流入变电站主变中性点的电流越大。此外,流入变压器的电流值还与变电站彼此间的电位差有关。因此,可以采取增大主变中性点接地电阻等措施来因减小流入变压器的中性点的直流电流来削弱直流偏磁现象。

The current of grounding electrode will cause a constantelectric field in a largearea of the underground. The DC biases of the transformers caused by the DC current through neutral points may damage the transformers. This paper presents a method for calculating the distribution of DC current in an alternating current network,including the ground circuit model of transformers and line and the underground electromagnetic field including grounding resistance and transformer ground potential. Taking a direct current transmission project as an example,the influence of parameters such as distance between substation and DC grounding electrode,soil structure,main transformer number,grounding resistance,line length and other parameters on the DC current of transformer are studied. The simulation results show thatthe farther away the substation is from the DC grounding electrode,the change in the number increased,grounding resistance increases,the line resistance increase can reduce the DC transformer into the deep influence of size;soil structure potential distribution of the significant,deep soil resistivity increases,causing potential near the DC grounding or greater current flows transformer neutral point is. In addition,the current value that flows into the transformer is also related to the potential difference between the substations. Therefore,we can increase the main transformer neutral point grounding resistance and other measures to reduce the DC currentto the neutral point of the transformer to weaken the DC bias phenomenon.