Review and Evaluation of Stray Current Mitigation for Urban Rail Transit

Stray current causes inevitable corrosion to structures near electric transportation systems, especially in DC urban rail transit. The paper considers the issue of stray current mitigation discussing what can be done for design and existing systems, sticking to applicable standards and consolidated protection practice. Mitigation measures may be devised for a new constructed system, such as the optimization of traction substation positions, reducing the longitudinal resistance of the running rails and return circuit, and using an additional stray current collection system (to be included in the track bed during construction). As for an existing system, besides increasing the total cross section of the aforementioned return circuit and stray current collection system by adding parallel conductors or cross-bonds, it is recommended to employ static converter units (e.g. negative resistance converters) to control the stray current in the return circuit. These units can be deployed in specific points where analysis or measurement indicates the large rail potential or incipient corrosion is spotted out.