Enhancement of power supply voltage quality at electric centralization stations on dc-electrified railways

This paper investigates the issue of voltage distortion in the 0.4 kV power supply at electric centralization (EC) posts. Significant voltage distortion may trigger an emergency switch to the backup feeder, potentially leading to failures in railway automation and telemechanic systems. To analyze this problem, a series of field measurements were conducted to assess the quality and harmonic composition of the supply voltage at an EC post. The experimental results revealed a direct correlation between the degree of voltage distortion and the load current on the adjacent traction substation. Using computer simulation tools, a detailed model of the traction substation, including the power supply lines to the EC post, was developed. Based on this model, optimal parameters for a passive LC filter tuned to suppress the 11th and 13th harmonic components - dominant under the 12-pulse rectification scheme - were calculated. A prototype harmonic filter was then constructed and integrated into the power supply line of the EC post. Post-installation field measurements were carried out to evaluate the voltage quality improvement. The results confirm the effectiveness of the selected filter in reducing both the total harmonic distortion (THD) of the voltage and the individual harmonic components of the 11th and 13th orders. During the entire four-month trial operation period, no emergency power transfers were recorded at the EC posts. The findings of this study can be applied to similar systems within DC-electrified railway networks, taking into account variations in rectification schemes and non-traction load power supply configurations.