Paper Title
Dynamic Distribution and Suppression of Vehicle-Rail Grounding Return Current in Emu Bogies

Abstract
The advancement of urban rail Electric Multiple Units (EMUs) imposes stringent requirements on grounding systems to ensure operational integrity. Transient topological variations in the vehicle-rail grounding path during operation can induce deleterious effects, most critically, unbalanced rail currents that compromise the reliability of track-based signaling systems. To address this challenge, this paper introduces a hybrid modeling approach, integrating a comprehensive 3D circuit model of the entire EMU with a detailed 3D Finite Element Analysis (FEA) of the bogie. Validated against empirical field data, the analysis quantitatively demonstrates that the grounding current from the leading axle is the principal contributor to rail current imbalance, causing it to exceed the 5% operational safety limit by reaching up to 10.81%. An effective optimization strategy, involving the strategic removal of the grounding connection on this specific axle, is proposed and verified. Simulation results confirm a successful reduction of the imbalance rate to below the 5% threshold, thereby restoring signaling integrity. The findings provide a validated design methodology and critical insights for optimizing EMU grounding systems to enhance both operational safety and electromagnetic compatibility in modern rail networks. Keywords - Urban Rail EMU, Grounding Return Current, Unbalanced Rail Current, Bogie Electromagnetic Field, Finite Element Analysis (FEA), System Optimization.