Effects of earthing systems on stray current for corrosion and safety behaviour in practical metro systems

Running rails are used as the return path for the train current in most DC electrified rail transit systems. The resultant rail voltage causes stray current to return to the DC supply source via other paths, such as nearby metallic infrastructure. Stray current is the main cause of corrosion in metallic parts located in the railway proximity. This study reviews various earthing schemes including thyristor earthed, diode earthed, floating and solidly earthed and corrosion phenomenon in DC railway traction systems. Then, based on simulations, a comparative study of safety and corrosive effects of the stray current, produced by various earthing schemes is presented. The study is part of the concept designed to control the stray current at Tehran Metro Line 3. Results of the study have been validated by simulation studies using a multi-train simulation software tool and the system data from Tehran Metro Line 3. The study shows some interesting findings such as corrosion damage increases near traction substations.