Modelling of the Distribution of Return Traction Current Harmonics in Electrically Asymmetric Rails

Abstract

The distribution of return traction current harmonics in electrically asymmetric rails in AC feeder zone is considered. Modelling the traction current harmonics in rails allows to evaluate electromagnetic interference from rolling stock at an early stage and under the worst conditions for its safe operation. The return traction current that flows from rolling stock axles back to electrical supply substation is divided into two currents with different values in two rails due to their electrical asymmetry. The resulting differential traction current and voltage in two rails affect the railway signalling systems and can cause faults in track circuits operation. Rails as a path for return traction current are longitudinally non-uniform due to impedance bonds and track transformers connected to them. Modelling of non-uniform systems is usually carried out by presenting them in the form of series-connected multipoles, which correspond to track transformers and uniform traction lines between them. But such model is awkward and redundant for the problem under consideration due to the need to use excessive specific parameter values for all track circuits in the feeder zone. For the case of small rail asymmetry, the simplified model is proposed in the work. In accordance with it, the distribution of the total current of traction harmonic in two rails between train and traction substation is calculated. Then, using the asymmetry coefficients of the rails, the distributions of the differential current and voltage of harmonics in two rails between train and track transformer or between two track transformers are determined.