Research on the Influence of Metro Stray Current on Transformer DC Magnetic Bias

In the operation of urban rail transit, the stray current of the subway is generated and flows into the earth, resulting in different ground potentials of each substation, which causes the DC magnetic bias of the transformer. Firstly, this paper establishes the stray current distribution model of dual-terminal power supply mode of subway, and simulates the dynamic change of stray current by adjusting the change of subway position. Then, the COMSOL software is used to build the coupling model between the subway operation line and the urban AC grid, and the ground potential distribution characteristics during the subway operation are simulated and studied. Finally, based on the neutral grounding voltage obtained by simulation and the topology of urban power grid, the variation law of DC magnetic bias single current in each substation is analyzed. The research shows that when the local railway locomotive runs in the middle of the line, the leakage of the stray current of the subway is the most serious, which will produce greater induction potential, and the influence on the substations in different locations is intensified, which makes the magnetic bias current of each substation increase.