Boundary-Element Computation of Per-Unit-Length Series Parameters of Railway Lines

This paper deals with the efficient computation of per-unit-length (p.u.l.) series parameters of railway lines. These parameters are key ingredients of a multiconductor transmission-line (MTL) model that is intended for the estimation of the main properties of the noise current distributions along the railway-line conductors. In order to increase the level of accuracy of models based on railway track MTLs, the per-unit-length parameters must be computed by taking into account the real geometry of the rails and correctly modeling the earth-conduction effects. Under the quasi-TEM approximation, which is valid in a frequency range up to some megahertz, in this paper a boundary-element-method formulation based on the magnetic vector potential is proposed, which leads to a straightforward calculation of the p.u.l. impedance matrix. The computational burden is dramatically reduced by the implementation of the surface impedance boundary condition on the rails and on the aerial lines, and by substituting the fundamental solution with a Green's function satisfying the boundary conditions at the air-earth interface, thus avoiding the discretization of the lossy ground.