Multi-conductor transmission line model for electrified railways: A method for including responses of lumped devices

For studying the response to transients caused by lightning and other electromagnetic disturbance sources, electrified railway systems can be represented as a system of multiconductor transmission lines (MTL) above a finitely conducting ground. The conductors present in this system would be wires for traction power supply, auxiliary power, return conductors for traction current, the tracks, and finitely conducting ground. In contrast to conventional power systems, where the MTL system is usually only terminated at the line ends, there are lumped devices connected in series and as shunt along the railway network, for example, booster and auto transformers, track circuits, and various interconnections between conductors, influencing surge propagation. In this doctorial thesis a new method for incorporating lumped series and shunt connected devices along MTL systems is presented. Telegrapher’s equations, using the finite difference time domain method, are adopted for finding surge pulse propagations along the MTL systems, simultaneously solving for the lumped devices connected along the lines by means of Kirchoff’s laws for nodal currents and voltages using a circuit solver. As part of this work, case studies are carried out to determine voltages appearing across devices connected along MTL systems representative of a typical Swedish single-track electrified railway system, in cases of direct and indirect lightning strikes. The influence of soil ionization at the grounding points and the nonlinear phenomenon of flashovers between overhead wires and the poles are also investigated. The calculations made show that the devices connected along this system, which are needed for normal and safe operation of the railway system, and nonlinearities are affecting the surge current and voltage distribution and peaks appearing along the MTL system and across devices.