In order to study the DC characteristics of the AC grid transformer bias caused by the stray currents in the urban rail transit dynamic operation, this paper first derives the "rail-drain network-structure steel-earth" four-layer double-sided power supply resistor network analytical model and the general mathematical model for the transformer bias DC caused by the stray currents. Then by using the CDEGS(current distribution electromagnetic fields grounding,soil structure analysis)ground analysis software, a "rail transit system-substation AC power system" coupling simulation model is established based on a 500kV substation in Shanghai and its nearby rail transit. The stray currents on the traffic side, the DC change rules on the transformer neutral points and their influencing factors are studied, and the correctness of the simulation model and the conclusions is verified by comparing with the field measured data. The results show: Based on the 500kV substation in Shanghai and its nearby rail transit simulation model, a single train operation can cause a maximum of 2.3A magnetic bias DC of the 500kV transformer, and a maximum of 7.1A magnetic bias DC of a transformer when multiple trains operate in both directions. Simulation results agree highly with the on-site measured results, which is statistically significant. The magnitude of the current amplitude at the neutral point of the transformers mainly depends on the relative position of the substation and the subway, the transition resistance of the rail to the ground, the soil resistivity, and the wiring modes of the substation. Finally, the simulation in this paper proves that a better DC suppression effect will be obtained in the 500kV substation when a 3 current-limiting resistor is installed at the neutral point of the transformer. © 2022 Power System Technology Press. All rights reserved.
