Assessment and Management of Metal Path Stray Current Intrusion in Urban Power Grids

The dynamic stray current of the subway invades the urban power grid, resulting in the DC bias hazard of the transformer. In order to explore the distribution law and influencing factors of metro leakage current metal path intrusion into urban power grid, a DC bias analysis calculation model considering the direct coupling relationship of the field and road is established, the distribution characteristics of stray current in the urban power grid are solved, and a method is proposed to determine the bias risk of track stray current by using the shunt coefficient of the neutral point loop of the main transformer. In this paper, the simulation of DC current and low-frequency measured stray current is used to verify that the method has reliable practical value. On this basis, the simulation analysis of the influence law and characteristics of the main variable shunt coefficient by different system parameters shows that the DC bias calculation model proposed in this paper can effectively warn the risk of stray current bias. When the stray current of the subway propagates in the urban power grid, the smaller the grounding resistance of the substation, the larger the shunt coefficient of the neutral point loop of the main transformer, and the larger the shunt coefficient of the neutral point loop of the main transformer when the resistance of the grounding transformer and the transmission line is small (such as the number of returns of the transmission line is less or the line is shorter).