Railway Signaling System Interference by Unbalanced Traction Harmonic Current: Mechanism, Modeling, and Solutions Based on Engineering Practice

The rapid development of railway electrification has led to signaling relay malfunctions and locomotive urgent braking accidents caused by unbalanced traction harmonic current (UTHC), which seriously threaten transit safety. This article presents a comprehensive study with a mechanism–modeling–solution approach that addresses the practical issue of UTHC interference in signaling systems and provides theoretical support for further research, relying on an actual case. Based on the mechanism analysis of UTHC interfering with the on-board and ground signaling terminals, UTHC and its induced harmonic electromotive force (EMF) on both the terminals are accurately modeled. The proposal and evaluation of solutions are supported by mathematical analysis of the relationship between traction-side current and signaling-side induced EMF. A low active loss passive filter with high filtering effect was designed and connected to the traction network for the actual case, effectively addressing the high-frequency harmonic resonance risk in traction power supply systems (TPSSs) and the harmonic interference issue in signaling systems. Field tests validate the feasibility and effectiveness of this solution. Accounting for cost constraints, guidelines for reducing current unbalance between two rails or avoiding choke transformer core saturation are developed based on a comprehensive sensitivity analysis of traction current unbalance coefficient and signaling equipment parameters.