Unbalance and voltage fluctuation study on AC traction system

Abstract

This paper presents the purpose of determining the effects caused by the railway traction load on the Electrical Grid System. One of the major issue in AC traction system is, traction loads are connected to single phase supply which results in voltage unbalance at point of common coupling (PCC) with the utility three-phase system. Unbalanced voltages can result in adverse effects on equipment and on the power system. This is aggravated by the fact that a small unbalance in the phase voltages can cause a disproportionately larger unbalance in the phase currents. Under unbalanced conditions, the power system will suffer more losses and heating effects and be less stable. Another major problem in the traction system is the voltage fluctuation caused by sudden shifts of the traction loads. A switch of traction load from one supply section to the adjacent section connected to a different substation gives rise to a step change in voltage which again gives cause to fluctuations in the voltage of the public grid and affects the operation and performance of connected voltage sensitive loads. The above impacts are analyzed for the Eastern Denmark Railway System which shall undergo a major change and renewal in near future due to the electrification of several existing lines. The Rail network under this study has total track length of 482 km with 65 railway stations, supplied by 15 traction substation (132/25kV). This paper presents the challenges involved in simulating the traction system using DigSilent software. Various challenges while modeling the traction network and calculation of power consumption by traction loads are discussed in this paper with the help of hand calculation and simulation results in time domain plots.