Development of a Simulation Model to Design Lightning Protection Measures for an Overhead Railway Traction System in South Africa

An advanced external and internal Lightning Protection System (LPS) was developed and analyzed using MATLAB/Simulink for a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$25 \text{kV}, 50 \text{Hz}$</tex> electrified railway line between the coal mines of Richards Bay and the harbor, an area with extremely high lightning Ground Flash Density (GFD). The LPS aimed to prevent dielectric breakdown of insulating components and magnetic saturation of the traction transformer during direct and indirect lightning strikes. The study evaluated three lightning current injection points: the railway mast, overhead catenary conductor, and pantograph interface. The external LPS employed Extended Mast Terminals (EMTs), double-shielded down conductors, shield wires, and ground electrode networks to safely dissipate lightning-induced transients. Optimal EMT and shield wire elevations were determined using the Rolling Sphere Method (RSM) to maximize shielding effectiveness. Internally, the system used idealized Metal-Oxide Varistors (MOVs) at key points, the mast, conductor, and pantograph, to protect sensitive electrical components from overvoltages. Simulation results showed that without an LPS, lightning strikes could cause catastrophic dielectric failure and transformer saturation due to large transient overcurrents. With the LPS in place, MOVs successfully clamped these surges, mitigating harmful effects and ensuring system integrity. The framework proved scalable and adaptable for similar high-voltage railway systems in lightningprone regions, enhancing infrastructure resilience against severe electromagnetic disturbances.