Evaluation of the impact of urban rail system on the distribution of DC currents in the power grid considering multi-train density

The metro system plays a crucial role in megacities due to its environmental friendliness and high capacity. However, stray currents generated in the metro system can interfere with the urban power grid, leading to DC bias in power transformers and posing a safety threat to the power system. The different train densities in the metro system meet people's commuting needs at different times of the day, but they also affect the severity of the DC bias at the surrounding power substations. However, the relationship between train density and the magnitude of DC currents flowing into the power grid remains unclear. In this study, a coupling model of the multiple metro lines and the power grid is launched to evaluate the impact of the train densities on substations under different operational conditions. The results indicated that train density significantly influences the magnitude of DC currents entering the substations, particularly those near multiple metro lines and traction power substations. Furthermore, by studying the DC current distribution in the whole power grid under various train densities, we discovered a strong positive correlation between the stray energy exchanged between systems and the train density.