Modelling of traction power supply systems with nonlinear stationary loads

Abstract

The aim was to develop digital models of traction power supply systems with nonlinear stationary loads in order to determine asymmetric and non-sinusoidal modes. To this end, methods based on phase coordinates were implemented in the Fazonord software package (version 5.3.4.1–2024). The models included the following elements: 220 kV transmission lines, 40 MV·A transformers, 25 kV traction networks of double-track sections and a converter unit powering the industrial transport power supply system. The developed models identified asymmetrical and nonsinusoidal modes during the movement of a train on a specific section of the main railway. It was demonstrated that the nonlinear stationary load generated by a six-pulse converter results in an increase in harmonic coefficients at the 10 and 220 kV inputs of the traction substation feeding the rectifier, exceeding 25% on the 10 kV busbars. This phenomenon should be considered when selecting means to reduce harmonic distortion. These include passive filters, active conditioners and new-generation electric rolling stock with four-quadrant converters. The maximum asymmetry coefficients on the 10 kV busbars of traction substations ranged from 4.8...9%. These values can be reduced down to acceptable limits using phase-controlled reactive power sources or balancing transformers. The presented models allow all the parameters of the AC railway power supply system to be adequately determined under stationary loads with nonlinear voltage-current characteristics. The developed method is versatile and can be used for calculating modes of supply and traction networks of various structures and designs.