The Distribution Analysis of the Ground Potential and Stray Current in Power Grid Under the Operation of Metro System

With the rapid development of urban rail transit, the direct current (DC) bias issue occurring in the transformer due to the stray current from the metro intruding into the power grid has become increasingly prominent, endangering the safety of power system. The harm of DC coupling between the metro and the power grid cannot be ignored. Herein, the distribution of DC current in the power grid under the operation of multiple metro lines is focused on, based on the coupling model between the metro and the power grid. The performances in terms of the distribution characteristics of ground potential and stray DC are compared, under the single-metro line and multi-metro line conditions. The impact of different train operation periods on the distribution of DC current has been explored. It is found that the potential difference between the grounding grids determines the magnitude of stray currents in the transmission lines. When the transmission lines are distributed along the metro lines, the average current in two metro lines increases by 45.3% when running in the same direction compared to a single line, and decreases by 57.9 % when running in the opposite direction.