Overview of Rail Potential Suppression Technology in Urban Rail Transit Running Rail Circuit Return System

Objective In the DC (direct current) traction power supply system of urban rail transit, excessive rail potential and stray current issues are persistent problems and common ailments for operational routes. Therefore, it is necessary to summarize and generalize the rail potential suppression technology in urban rail transit running rail circuit return system. Method Based on the situation and prominent issues of rail potential and stray current in operational lines in China, starting from the mechanism of DC traction power supply system return flow, the main factors affecting rail potential in the system are sorted. A rail potential suppression technology is introduced, some methods for suppressing overvoltage generation are compared and analyzed, such as parallel resistors, parallel capacitors, and incorporating locking current logic protection set values. Technical solutions for the novel rail potential limitation device with linked shielding doors, the intelligent stray current suppression type rail potential limitation device using IGBT (insulated gate bipolar transistor), and the flexible topology rail potential limitation device are presented. Result & Conclusion By implementing power electronic full-power converter topological units, the dynamic and flexible control of rail-to-ground voltage and current demonstrates a highly promising remedial measure for future comprehensive control of rail potential and stray current in running rail circuit return system. During the line design phase requirements of different systems, rail potential reduction can be met by increasing traction voltage, optimizing traction spacing, reducing longitudinal track resistance, and eliminating direct grounding of running rails in depot garages. Additionally, complete isolation of electrical systems between mainlines and depots and between different lines is also an important measure to suppress rail potential.