Assessment of a frequency dependent soil model impact on lightning overvoltages

A key aspect in the evaluation of the lightning performance of an overhead line is the tower grounding modeling approach. It affects the insulator string overvoltages and the ground potential rise (GPR). This work aims to assess the impact of the soil model i.e. using frequency independent and frequency dependent parameters. The developed grounding system model was implemented in the EMTP-ATP program. A RLC synthetized network is used instead of a constant lumped resistance. The RLC elements are derived from the rational approximation of the grounding system response obtained using a rigorous model based on the direct solution of Maxwell's equations in the frequency domain. An application example is presented, showing that the computed overvoltage is sensitive to the frequency dependence of the soil parameters. This effect is more pronounced for high resistivity soil.