Overview of stray current control in DC railway systems

In DC rail transit systems, the running rails are usually used as the return conductor for traction current. This arrangement mainly focuses on economic considerations, since it does not require the installation of an additional return conductor. Low resistance between the traction return rails and the ground allows a significant part of the return current to leak into the ground. This is normally referred to as leakage current or stray current. The amount of leaking current depends on the conductance of the return tracks compared to the soil; and on the quality of the insulation between the tracks and soil. The stray currents represent serious problems for any electrified rail transit system. The corrosion problem has been a major concern to the railway and other parties involved since the early days of DC railways. The stray currents create or accelerate the electrolytic corrosion of metallic structures located in the proximity of the transit system. This causes metal pipes, cables and earthing grids laid in the ground near the tracks have a much shorter life which is high importance in regard to safety and economy. Hence, great efforts and research have been carried out to control stray current in DC electrified rail transit system. Stray current control is essential in these railway transit systems where the rail insulation is not of sufficient quality to prevent severe corrosion to the rails and third-party infrastructure. Good control of stray current is also of direct benefit to the operational and safety aspects of the DC electrified railway systems; it could reduce the rail touch voltage. This paper provides an overview of control schemes currently applied to the DC traction electrified rail transit system.