Harmonics Analysis Due to Connecting an Electrical Traction to A 3-phase Power Supply System Through V/V Transformer

Abstract

The wide application and usage of electrical traction system presents utilities with planning and operation challenges. Electric railways impose several power quality problems to the utility grid. Such as generated large negative sequence components (NSCs), undesirable harmonics, cause system voltage and current unbalance. Harmonics and unbalanced voltage also may cause negative effects on the components of the power system such as: overheating the transformers and the transmission lines, vibration and cause torque reduction of rotating machines, additional losses of lines and transformers, interference with communication systems, malfunctions of protection relays, measuring instrument error. All these problems have become more and more significant. This paper is an attempt to quantify and assess the impact of electrical traction on the grid side through a V/V transformer. Firstly in this paper, the typical utility power grid and traction power supply system model are designed. Then, the traction system is integrated with the power supply system through a V/V transformer. Two cases of the connection are considered. The first case, when the traction system is connected to one side of transformer. The second case, when there is a balance traction load on the both transformer side. Finally, PSCAD simulation is used to analyze the power system quality and to estimate the harmonics that are generated in the traction and power supply system sides due to this integration. The simulation results show that, in the both cases, high levels of voltage and current harmonics are generated in the traction side. These harmonics are generated only on the phases that the traction is connected to them, while the other phase will not be affected. Also, it is observed that, the generated harmonics at the traction load side have also been transferred to the power supply system side though the transformer