Apparent Impedances and Distribution of Fault Currents for Solid Faults in 2x25kV Electric Railway Systems

This article analyzes the distribution of short-circuit currents in 2×25kV electric railway systems, as well as the apparent impedances seen by the distance protection for solid faults. The analyzed short-circuit types are catenary-to-ground, feeder-to-ground and catenary-to-feeder. The line model is based on a 2×2 matrix in cases with only one track, and on 3×3 and 4×4 matrices in cases with two tracks. Simplified analytical models are deduced, neglecting transformer impedances and train currents in order to explain more clearly the distribution of currents under short-circuit conditions, as well as the parabolic behavior of the modulus of apparent impedances as a function of the distance up to the fault. The effect of transformer impedances is shown with the help of the numerical solution of the network.