Practical model for tower earthing systems in lightning simulations

In assessing the lightning performance of a transmission line with an Electromagnetic Transient (EMT) approach, the representation of the earthing system or tower footing can have a major impact on the simulation results. In this paper, a practical circuit for a direct implementation into an EMT software is presented, which uses a minimum of input parameters to represent a common four rod tower footing arrangement. Based on an available description of the frequency-dependency of a single rod in soil and a description of the ionization in soil for a single rod, a combined circuit model is developed for a tower earthing arrangement with four rods in a square arrangement. This approach takes into account the merging of the ionization zones from each rod.