Objective To comprehensively understand and resolve the stray current issues arising from rapid metro development, it is necessary to focus on stray current diffusion mechanism and suppression strategies in DC traction power supply systems by constructing accurate circuit models and diffusion models.

Method The complex main-line return system distributed circuit is simplified into a lumped circuit, and an equivalent model of the depot and parking lot is established based on the specific characteristics of the return equipment, thereby forming a complete circuit model of the DC traction power supply system. Using the direct BEM （boundary element method）, regional equivalence is performed on the spatial and conductor structures in the metro return system to establish a stray current diffusion model for accurate simulation of propagation process in complex structures. A joint simulation of the circuit model and the stray current diffusion model is conducted to simulate the diffusion distribution of stray currents along the entire line. The validity and accuracy of this joint simulation are verified through comparison with CDEGS simulation results. Taking a domestic metro line as an example, the stray current distribution and its relationship with DC interference along the metro line are analyzed, based on which targeted stray current suppression strategies are proposed.

Result & Conclusion Stray current diffusion concentrates in sections with large substation intervals, as well as near the depot and parking lot, with its distribution being positively correlated with the degree of DC interference. Consequently, both rail insulation strengthening strategy and intelligent conduction devices installation in depots and parking lots, can effectively suppress stray current diffusion, enhancing metro operation safety and stability.