变压器中性点串小电阻抑制直流偏磁的研究  

Transformer Neutral Series Low Resistance Designed against DC Magnetic Bias

作　　者：邱璆[1] 吴广宁[1] 任志超[1] 张一坤[1] 

机构地区：[1]西南交通大学电气工程学院,成都610031

出　　处：《华东电力》2012年第5期812-816,共5页East China Electric Power

基　　金：科技部国际科技合作项目(2009DFA72230);国家电网公司科技项目(2011-WG-4)~~

摘　　要：高压直流输电单极或双极不对称运行时,直流入地电流会使接地极附近的交流变电站地电位升高,从而导致直流电流侵入中性点接地的交流变压器,产生的直流偏磁将影响变压器正常运行。针对直流偏磁现象,提出了变压器中性点串接小电阻的方案,利用电力系统仿真软件PSCAD/EMTDC对接电阻后的交流输电网络进行建模,仿真分析了该方案的抑制效果,以及工频过电压和雷电过电压对中性点绝缘的影响,给出了串接电阻的建议值。研究结果表明:变压器中性点串接合适阻值的小电阻可以简单而有效地抑制直流偏磁电流,随着电阻值的不断增大,电流的衰减效果并不明显;故障情况下串接电阻后会抬高中性点的电压,建议取值的小电阻能够承受短时工频过电压和冲击过电压,不会对中性点的绝缘造成影响。When HVDC system works in monopolar or bipolar asymmetric ground mode, enormous DC earth-fauh cur- rent leads to the ground potential rising around AC substation nearby, which results in DC invasion into the AC trans- former with neutral grounding, then the generated DC magnetic bias may affect the normal performance of transform- er. Therefore, this paper proposes a scheme to use neutral series low resistance to restrain the DC magnetic bias. PSCAD/EMTDC was adopted to model the AC power grid connected with resistors; the restraint effect was simulated; the influence of frequent overvoltage and lightning impulse overvoltage on transformer neutral insulation was analyzed ; the value of series resistance was recommended. It is shown that transformer neutral series low resistance can restrain DC bias current simply and effectively. With the increase of resistance, the decay effect of current is not obvious. The series resistor will upgrade the voltage of neutral point in case of fault, so the value of low resistance is recom- mended to stand the short-time frequent overvohage and impulse overvoltage, thereby the transformer neutral insula- tion will not be affected.

关 键 词：高压直流输电 直流偏磁 中性点串电阻 过电压 

分 类 号：TM72[电气工程—电力系统及自动化]