A Field-Circuit Coupling Diffusion Model for Stray Current of DC Metro System

Stray current in the dc metro system is commonly assessed using circuit or electric field models. Circuit models cannot accurately represent the stray current diffusion due to the track bed and soil resistivity effect on rail-to-earth resistance (RE). Meanwhile, electric field models lack detailed device modeling, which hampers their ability to comprehensive stray current analyses. To overcome these limitations, a field-circuit coupling diffusion model (FCDM) for stray current is proposed. The electric field submodel is established through the direct boundary element method (DBEM) for the metro reflux system (RS) and obtaining the mutual resistance matrix. The circuit submodel of the dc traction power system (DPS) is established based on the behavior characteristics of the RS devices. The dynamic stray current diffusion is obtained by coupling the two submodels through the mutual resistance matrix. The accuracy and efficiency in solving large systems with massive textures of the proposed model are verified by comparing them with the field test data and other existing methods. The case shows that strengthening the RE for a length of 500 m on both sides of each traction power substation (TPS) can effectively reduce the earth potential gradient along the metro line.