Modeling of 25 kV electric railway system for power quality studies

25 kV, 50 Hz single-phase AC supply has been widely adopted in the long-distance electrified railway systems in many countries. Electrical locomotives generate harmonic currents in railway power supply systems. Single-phase traction loads also inject large unbalance currents to the transmission system and cause voltage unbalance subsequently. As the amount of rail traffic increases, the issue of power quality distortion becomes more critical. Harmonic currents and unbalanced voltages may cause negative effects on the components of the power system such as overheating, vibration and torque reduction of rotating machines, additional losses of lines and transformers, interference with communication systems, malfunctions of protection relays, measuring instrument error, etc. Therefore, the harmonic current flow must be assessed exactly in the designing and planning stage of the electric railway system (ERS). Harmonic current flow through the contact line system has to be accurately modeled to analyze and assess the harmonic effect on the transmission system. This paper describes the influence of electric railway system on power quality in 110 kV transmission system. Locomotives with diode rectifiers were analyzed. Electric railway system was modeled using EMTP-RV software. Currents and voltages were calculated in 110 kV and 25 kV network. Power quality measurements were performed on 110 kV level in 110/35/25 kV substation and analyzed according to IEC 61000-3-6.