并联直流接地极抑制上海区域直流偏磁的方法研究

在对直流偏磁产生原因及安装于变压器中性点的直流抑制装置进行简述的基础上,考虑上海区域多直流落点和多接地极的特点,提出了用并联直流接地极去抑制上海区域直流偏磁的方法。根据设计单位资料,对并联用特高压奉贤接地极、华新换流站接地极以及南桥接地极建立了电极模型并获取了各500 kV变电站等效电阻。根据上海区域地质结构和土壤电阻率实测数据,建立了由浅沉积层、深沉积层、基岩层以及地幔至地心层组成的4层水平分层土壤模型。以近景年上海区域电网主要拓扑结构,对直流接地极单独运行、并联运行进行了地表电位和变压器中性点电流计算分析。其中地表电位计算分为上海区域地表电位和各变电站地表电位,而变压器中性点电流计算分有无接入小电阻两种工况。计算结果表明,在并联运行方式中,各变电站的地表电位和直流电流都得到了有效控制。

DC Bias Suppression for Shanghai Region Using Parallel Connection of DC Grounding Electrodes

The mechanism of DC bias and the DC bias suppression equipments at transformer neutral point are described.Considering the feature of many DC grounding electrodes in Shanghai region,a method for suppressing DC bias using parallel connection of DC grounding electrodes is proposed.The DC grounding electrodes in Fengxian,Huaxin and Nanqiao 500 kV substations are modeled,and equivalent resistances for each substation are obtained according to the primal construction data.And a four-layer horizontal soil model is established including superficial sedimentary deposit,deep sedimentary deposit,bedrock deposit and earth mantle deposit by considering the geologic frame and the measured resistivity of different soil layer in Shanghai region.The earth potential and DC bias current of transformers in Shanghai region are calculated and analyzed in the cases of independent operation and parallel-connection operation of the DC grounding electrodes with the topological structure of the existing Shanghai power grid.The results show that the earth potential and DC bias current of each 500 kV-level substations can be efficiently suppressed.