Analysis of the power quality impact in power supply system of Urban railway passenger transportation - The city of Ulaanbaatar

Abstract

The urgency and expediency of additional passenger transportation by urban railway as an extension of the transport infrastructure of megacities has been proved. The fact that the urban railway uses AC 2x25 kV, which is uses to out of the three phases of city's power supply system negatively impacts. Thus, it creates a significant asymmetry. In this paper, a comparative analysis on the negative sequence component of the voltage unbalance, which occurs in the nodes of connection of traction substations through both a three-phase transformer or a Scott transformer are been carried out. A mathematical method was created for determining the negative sequence voltage unbalance factor is based on the phase coordinates and symmetrical components methods. The results show that the Scott transformer provides a more symmetrical load distribution to the three-phase electric grid, when compared to the three-phase transformer and was verified using a simulated model in the Matlab program. Consequently, the use of a Scott transformer has better symmetrising abilities than a three-phase transformer, which gives it a significant advantage in the traction power systems.