Integrated modelling of audiofrequency track circuits

A 25 kV AC railway system is considered, where the variable length (10-20 km) section comprised between two electrical substations (ESSs) is equipped with audiofrequency track circuits (both transformer and s-bond coupled). The railway system is modelled using multiconductor transmission line (MTL) approach; the ESSs, the vehicle and the tuning unit of the track circuit are described by means of their equivalent circuit. The results consist of the analysis of the influence of s-bond circuits on the rail-to-rail impedance and the calculation of the disturbing voltage at the receiver terminals produced by samples of locomotive traction current from field data.