A Monovoltage Equivalent Model of Bi-Voltage Autotransformer-Based Electrical Systems in Railways

This paper presents an equivalent model that allows representing bi-voltage autotransformer-based systems (such as 2 × 25 kV ac, 2 × 15 kV ac) as if they were monovoltage systems. This model can be used for symmetrical (such as 2 × 25-kV 50-Hz systems) and unsymmetrical (such as 12/24-kV 25-Hz systems) configurations. It is based on two simplifying hypotheses that establish relationships between currents and voltages in the positive and negative phases. These hypotheses are discussed and the accuracy of the model is evaluated by comparing the results with a detailed conventional model of power-supply systems.