The impact of the frequency dependence of soil electrical parameters on lightning overvoltages developed in a 138 kv transmission line

This study evaluates the overvoltages developed due to direct lightning strokes to a 138-kV transmission line tower top comparing constant and frequency-dependent soil parameters. ATP(Alternative Transients Program) was used to simulate the phenomena. The inclusion of the frequency-dependent soil parameters causes a percentage decrease of the overvoltage peaks when compared with constant soil parameters of around 15% to 33% for first strokes considering values of soil resistivity of 500 Ω.m and 2.500 Ω.m. It was also studied the counterpoise cables length reduction in order to maintain equivalent overvoltage levels to those of simulations with constant parameters. This reduction ranged from 25 to 55%, which could contribute to economic gains as well as operational efficiency in the grounding systems and transmission line construction time. Therefore, disregarding the frequency dependence of the soil parameters in simulations may lead to an overly conservative estimation of the lightning performance of the transmission line.