Modeling Non-Sinusoidal Modes in Electrical Networks Supplying Power to Traction Substations for Electromotives Operation with Four-Quadrant Converters

Abstract

Rectifying electromotives are characterized by non-linear voltampere features generating higher harmonics into supply networks which occurs on the background of the following negative effects: reduction in the equipment service life, energy accounting distortion, resonance processes occurrence, etc. Therefore, the task of reducing harmonic distortion levels in networks adjacent to traction substations of AC railroads is of higher significance. The level of HH generation depends on electromotives structural features. Electrically-powered rolling stock with zone-phase control generates significant harmonic distortions; in this case, power losses in traction network increase and power supply reliability decreases. New generation electromotives equipped with asynchronous motors (AM) and 4q-S converters allow one to generate current curve close to sinusoidal and reduce harmonic distortions. In order to produce qualitative assessment of harmonic distortions reduction level for moving electromotives with AM, simulation modeling of typical 25 kV traction power supply system s nonsinusoidal modes for two types of the electromotives used: VL-80R with zone-phase control; UTY-1 with asynchronous motors and four-quadrant converters. The procedure of nonsinusoidal modes determining is based on technology of electrical power systems modeling in phase coordinates with application of lacelike networks with fully-meshed topology. Such schemes are built using elements with frequency-dependent parameters. Therefore, they can easily be translated into HH frequencies. Dependences on current parameters mode, characterizing harmonics sources, do not considerably affect calculations results. It is due to the fact that the first harmonic is dominating and the sources parameters are determined by preliminary mode calculation on the basic frequency. The approach suggested is versatile and can be used for studying nonsinusoidal modes in specific and advanced traction power supply systems. The modeling results indicated that the issue of higher harmonic distortions level in networks, supplying traction substations, can be fully resolved when existing engines are replaced with new generation electromotives with asynchronous drives and four-quadrant converters.)