Mathematical modelling of dynamic soil resistivity under transient conditions

It is critical to design an earthing system for transient conditions such as lightning strikes, over voltages, surges etc., for which the estimation of soil resistivity under transient conditions is essential. The soil resistivity varies dynamically under transient conditions and hence the estimation of dynamic soil resistivity is difficult process. In this work, under lightning impulse conditions, the dynamic soil resistivity profile is created by simulations considering soil ionization for different soil resistivity, ionization and deionization time constants. Based on the simulation results, dynamics soil resistivity modeled mathematically to compute ionization and deionization resistivity. The results infer that the dynamic soil resistivity depends on permeability, permittivity and lightning impulse rise time and does not depend upon earth electrode dimension.