The effects of earthing strategies on rail potential and stray currents in DC transit railways

When the running rails are used as the traction current return conductor in a rail transit system, the control of rail potential and stray current is an important aspect of system design. The choice of earthing strategies within the transit system has a profound influence on rail potential and stray current control. The tasks of controlling both rail potential and stray current are conflicting, therefore a balance has to be struck between the two. This calls for a comprehensive study before a strategy is chosen. Previous research work at the University of Birmingham in collaboration with Cegelec Projects Limited established an approach to the definition of the performance criterion for both rail potential and stray current. A computer program was also developed to simulate the performances of systems against the defined criterion. The simulator takes account all relevant system parameters that affect the power supply system. This paper describes the follow-on work, following further developments on the simulator, having taken account the latest technological advancements on rail potential control devices (RPCD). The merits of floating earth in combination with RPCDs are examined in detail. The simulation model has been validated against practical test results. Sample simulation results for a test track are presented for analysis