A method for including the responses of lumped devices into multi-conductor transmission line model for electrified railways
Abstract: The electrified railway system consisting of overhead lines for traction power supply, auxiliary power, return conductors for traction current and the tracks can be modeled as a system of multiconductor transmission lines (MTL) above a finitely conducting ground. There are several lumped devices connected in series or in parallel along this MTL and the response of the MTL to electromagnetic transients need to be solved along with the device response. In this licentiate thesis a method for incorporation of series and shunt devices along multiconductor transmission systems are addressed. For finding the surge voltage and current pulse propagations along the transmission line system telegrapher’s equations using the finite difference time domain method are solved. The lumped components connected along the lines are solved by means of Kirchoff’s laws for nodal voltages and currents using a circuit solver software, and the nodal voltages and currents are made available to the MTL model for each time step. The method presented is first verified by comparing simple lumped resistive and inductive components with the finite difference time domain method, where the lumped components are accounted for by representative differential equations. Later case studies on the influence of common traction transformers, i.e., booster transformers and autotransformers, and track circuits, i.e., relay and rectifier units, on a multiconductor transmission line system representative of a typical Swedish single-track electrified railway network are made. The calculations made in this work shows that the components connected along this system, which are needed for safe operation of the railway system, do affect the surge current and voltage peaks and distribution along the multiconductor transmission system. These effects are also discussed in this thesis.
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