The intrusion of earth current into the neutral point of grounding transformers can pose significant threats to grid power quality. This issue is particularly prevalent in railway transit systems, which are often subject to ubiquitous harmonic pollution. A major challenge in modeling earth current distribution stems from the complex coupling of traction power supply system from the railway system and alternating current (AC) transmission systems, further complicated by varying leakage currents from diverse tracks. This paper, for the first time, introduces a lumped parameter model designed to address these challenges. The model tranforms the coupling between the traction power supply system and the AC system into a point coupling, aiding the creation of a ground current distribution calculation model. Both mathematical and simulation models are provided and validated against field measurement results. This model is anticipated to serve as a practical foundation for the effective mitigation and management of earth current concerns in railway systems.
