Influence and Analysis of Urban Subway on DC Bias of Power Transformer

In urban metro rail transit, the DC power supply mode is adopted in the power supply traction network. Part of the traction current leaks to the ground through the rail to form stray current, which causes the DC bias phenomenon of the surrounding power transformer. Taking a 220kV power transformer DC bias caused by subway stray current as an example, this paper comprehensively analyzes the invasion principle, invasion source classification, field data and DC bias treatment scheme, the influence and law of subway on DC bias of AC power grid transformer are clarified, and the defense scheme of DC bias caused by urban power grid on subway is proposed, so as to provide effective basis and suggestions for the analysis and prevention of the adverse impact of subway rail transit on power transformer.