Modeling of the traction current harmonics distribution in rails

Abstract

Electrified railways are one of the most powerful wide frequency range sources of disturbances that interference on signaling and radio communication systems. This is especially true for new types of vehicles equipped with electronic static converters with pulse width modulation (PWM), from which high-frequency interferences in rails can have frequencies up to several tens of kHz.To ensure the electromagnetic compatibility (EMC) of new types of rolling stock with signaling and radio communication systems, they are subjected to an acceptance procedure that includes on EMC tests in accordance with European and national regulatory standards and norms. But under some unfavorable operation conditions for the trains that were successfully tested and are in operation with old vehicles on the same lines (sometimes with old feeding system), the disturbing current generated by vehicles may reach values greater than the allowed values. As such unfavorable operational conditions may be considered increasing number of trains, low distance between track circuit receiver and vehicles or supply substation, low rail-to-earth conductivity and conductivity of earth. To proof the electromagnetic compatibility (EMC) between rolling stock and signalling systems it is need accurate modeling of the test cases with taking into account particular operation conditions.The aim of the work is to establish mathematical and computer model for distribution of traction current harmonics in direct feeding traction network with multiple vehicles in feeder zone. This model is an evolution and simplification of models represented earlier.The work has been performed in order to proof the electromagnetic compatibility of new trains equipped with electronic static converters with existing traction lines and has been used during tests of new types of train.The model has been simplified as follows. The lines with equal or close to each other potentials are represented as a single line with equivalent electrical parameters. The disturbing vehicles are modeled as sinusoidal current sources with several set of frequencies that are represented by currents vector. Only return current harmonics with frequencies that lie in frequency range of track circuit receiver were considered. Depended of simulation aim the values of harmonics are taken as values measured during train tests or as the maximum interference values according to norms.The distribution of the traction return current harmonics was computed for AC direct feeding traction network 1x25 kV with two-side ESS and with 1 to 5 vehicles in feeder zone. The maximum interference from trains is in the areas nearest to trains and also to the point of connection of return feeder to rails (at ESS terminals). The traction harmonic current in rails are increased with increasing of train number in feeder zone and with decreasing of the rail-to-earth conductivity.The interference at 25 Hz in the rails area near the ESS for one locomotive in feeder zone don’t exceed a limit value of 1 A even in unfavorable operation conditions for of the rail-to-earth conductivity equal 0.02 Sm/km. If number of trains are increased (from 1 to 5) the interference at 25 Hz also increased and it values at rail-to-earth conductivity equal 0.02 Sm/km reach to 1.073 A for two locomotives and to 1.233 A for five locomotives, that exceed the limit value of the interference in rails at 25 Hz.