Fault analysis on AC railway supply system

A short circuit fault in an AC railway supply system could have undesired consequences; including high-amplitude current flow in the power path, the rail potential rise in the fault vicinity. This paper studies the problem of the rail voltage rise in Tehran-Karaj railway system by the use of a steady state circuit model for the AC autotransformer during a phase-to-ground fault. By using this model, all the currents and voltages of the system can be easily calculated for all possible short circuit fault locations. With the help of the derived analytical model, one can also predict the possible fault locations which may cause the protection system to operate. The estimation of the system currents and voltages levels after the fault helps us to design more effective and economic protection systems and also to estimate the fault location. Transient effects are ignored in the proposed model and the equivalent system represents only the steady state model of the supply system after the fault.