WIT Press

A Mixed AC/DC Model For Railway Power Systems


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J. Muñoz-Riesco, E. Pilo, A. Fernandez & P. Cucala


A method to study railway power supply systems with AC power distribution networks and DC power feeding is presented in this paper. The aim of this work is to obtain a DC model of the whole system in which AC networks are converted into equivalent DC ones. Relationships between AC and DC quantities on both sides are set using the equations of multiple bridge rectifiers as described in the literature. Particular DC models for transformers and 3-phase lines are used to represent the corresponding voltage drops. Specific base quantities are used for AC and DC parts of the circuit in order to obtain a simplified circuit. This model is used to solve a DC load flow problem. Real values of voltages, intensities and power flows can be obtained by using the proper base quantities. Additionally a correction has to be made to improve the power flow results calculated previously, due to pure resistive representation of transformers and AC lines, so a fine approximation is achieved. Keywords: railways, AC/DC power supply system, equivalent DC model. 1 Introduction Railways’ power systems usually have an AC division (zones close to distribution networks) and a DC one (zones close to trains). This feature makes those structures difficult to deal with when an electrical study is required to be practised. Homogenization of the electrical circuit to AC or DC helps it to be solved by means of a load flow problem. Converting the whole circuit to AC provides exact results, but it involves a great amount of variables and calculations.


railways, AC/DC power supply system, equivalent DC model.