地铁杂散电流引起变压器直流偏磁抑制方法

Restraining Method of Transformer DC Bias Caused by Metro Stray Currents

针对城市地铁运行时泄漏的杂散电流会引起沿线变压器直流偏磁问题,提出一种基于碳化硅PiN二极管的偏磁抑制方法。首先,建立杂散电流分布模型并采集现场地电位实测数据,明晰了地铁运行下城区整体大地电位的数值分布特点。然后利用碳化硅PiN二极管在直流电压和故障电流下的电压阻断能力及电流导通特性,提出了基于碳化硅PiN二极管的变压器直流偏磁抑制电路结构与工作流程。最后基于PSCAD/EMTDC仿真平台搭建了城市电网110kV变电站主变直流偏磁仿真模型,验证了偏磁抑制方法故障电流导通能力和偏磁直流抑制效果。仿真结果表明:电网故障时,偏磁抑制方法瞬时导通,继电保护迅速动作跳闸;变压器实施偏磁抑制后,中性点直流电流被阻隔,磁滞回线、一次侧绕组电流及励磁电流畸变率降低,直流偏磁得到有效抑制。

Aiming at the problem that the stray currents leaked during the operation of the urban subway have caused the DC bias of the transformers along the line,a DC bias suppression method based on the SiC PiN diode is proposed in this paper.First,a stray current distribution model is established and the ground potential data are measured and collected,which clarifies the numerical distribution characteristics of the whole earth potential in the downtown area during the subway operation.Then,based on the voltage blocking ability and the current conduction characteristics of the SiC PiN diode at the DC voltage and the fault current,the structure and working flow of the DC bias suppression circuit for the transformer based on the SiC PiN diode are presented.Finally,based on the PSCAD/EMTDC simulation platform,the DC bias simulation model of the main transformer in the 110kV substation of the urban power grid is established to verify the fault current conduction ability and the effect of the DC bias suppression.The simulation results show that the DC bias suppression instantaneously conducts when the power grid is faulty with the relay protection quickly act in tripping;After the transformer applies the DC bias suppression,the neutral DC current is blocked,the distortion rates of hysteresis loop,the primary winding current and the excitation current are reduced,and the DC bias is effectively suppressed.