Simulation Study of the Influence of Stray Current on DC Bias of Power Transformer

The running of subway rail transit can generate stray currents. This is a current that causes severe corrosion of the buried metal near the subway, and also generates DC bias, which affects nearby power transformers. There are few studies related to the influence of DC bias created by stray current on power transformers. This makes it difficult to determine the impact of subway rail transit on the DC bias of nearby power transformers. To explain the effect of stray current on the DC bias of the power transformer, the characteristics, master sheets of stray current and the principle of DC bias of stray current are analyzed, and a power transformer model of stray current generating exciting current is established. The harmonic components in the stray current are simulated and analyzed. The simulation results show that the track insulation aging caused by subway operation will generate stray current, which will flow into the grounding grid and cause DC bias of the neutral grounding transformer, and then make the transformer core saturated. The amplitude of harmonic component and excitation current will increase with the increase of stray current.