Mathematical modelling and computer simulations of induced voltage calculations in AC electric traction

This thesis studies the foundation of a new method to calculate the induced voltage into line-side signalling circuits using numerical modelling technique. The need for accurate calculations of induction due to the high power overhead line has prompted the development of such a new approach. Due to the complexity of the railway systems, measurements are not always possible. An alternative approach, either analytical or numerical analysis, is required. The analytical method has been developed and applied since the beginning of electrification. Although this method provided reasonable results, it has certain limitations with respect to frequency range, and hence accuracy. The development of computers provided us with a new and exciting analysis, that is, mathematical modelling techniques. This project devised a new method based on the finite difference time domain to calculate the impedances of the rail track and overhead line and the longitudinal induced voltage into nearby signalling systems. The method is simple and has been developed using known software (MATHCAD & APLAC) in order to reduce any additional cost that may arise. Calculations have been carried out for uncompensated systems (no booster transformer) and compensated systems for various overhead catenary configurations relating to one-track and two-track layouts in open areas. Two different overhead ratings namely 1250 Amps and 760 Amps have been considered. The signalling cable can be placed at either side of the track(s). Both positions haven been considered as well as normal and fault conditions. The position of the signalling cable has greater effect for one-track case than two-track or more. The level of induction is also greatly related to the number of the track used (i.e. worse induction for one track than for two, four or more). The design of the booster transformer is very important in order to reduce any induction, this becomes more evident at short circuit conditions when the magnetising current effect is more evident.