Evaluation Method for Intrusion Current in Urban Power Grid Caused by Metro Stray Current Based on Field-Circuit Coupled Iterations

The rapid development of rail transit has caused growing concern about metro stray current (MSC) intrusion in urban power grid (UPG). MSC intrusion inevitably causes risks such as transformer DC bias and grounding grid corrosion. Accurate evaluation of MSC intrusion current in UPG is crucial for addressing these challenges. Existing research indicates that MSC intrudes UPG through two distinct paths, respectively the metal sheath and the earth. Considering MSC in the metal path follows Kirchhoff's law, while MSC in the earth path satisfies the electric field diffusion equation. Therefore, to accurately obtain MSC intrusion current distribution in UPG, we proposed an evaluation method for intrusion current in UPG caused by MSC based on field-circuit coupled iterations. Firstly, a metro-UPG dual network coupling model was established, including both the earth path and metal path. Based on resistive network and injection current of the model, the nodal voltage equation was formulated. Then, the earth potentials induced by MSC diffusion in the earth were obtained by the complex image method for each grounding branches. Next, the earth potentials were equivalent to current sources via Norton's theorem, which in turn updates the injection current. Finally, MSC intrusion current was evaluated through iterating nodal voltage. The accuracy was verified with field results. Moreover, the critical path and influence factor of MSC intrusion current were analyzed. The proposed method supports the evaluation and suppression of MSC intrusion UPG.