Calculation of the Voltage Unbalance Factor for 25kV-50Hz Railway Substations

This paper presents a method to determine the voltage unbalance factor for a 25kV/50Hz railway substation taking into account the power drawn by the trains. In order to correctly size a balancing system to be associated with the substation, it is necessary to calculate with precision the voltage unbalance factor. Some authors proposed empirical formulas intended to determine the voltage unbalance factor using the apparent powers. However, because they don't consider separately active and reactive powers, these formulas are inaccurate and become unusable when a balancing system is connected.In the first part, this paper proposes a substation modelling which allows to calculate the upstream line voltages considering the power consumption of the substation. In the second part of the paper, the same approach is applied considering the connection of an unbalance compensator based on a Steinmetz circuit controlled by AC choppers.