This paper presents the modeling and simulation of the voltage unbalance in the power supply system of an AC electrified railway. The operating voltage at the traction substation is obtained by MATLAB/SIMULINK program and the voltage unbalance is evaluated by considering the voltage unbalance factor (VUF). Suvarnabhumi Airport Rail Link (ARL), in Bangkok, Thailand, is chosen to be a case study. The ARL is supplied by two single-phase traction transformers connected as a cyclic permutation of phases. According to the extension plan of the ARL, four service scenarios with different headways, auxiliary loads and total weights of the trains were simulated to study how the different scenarios influence the VUF at the three-phase side. It can be summarized that at the same headway, the VUF was increased when the train weight and auxiliary power load were increased. In case of different headways, the longer the headway, the more voltage unbalance. The extension plan of the ARL in the near future can be achieved with the voltage unbalance level under the maximum allowable value.
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