The Impact of the Frequency Dependence of Soil Parameters on the Lightning Performance of Transmission Lines

This study assesses the lightning performance of 230- and 138-kV transmission lines under the assumptions of constant and frequency-dependent soil parameters. An electromagnetic model was used to simulate the response of tower-footing electrodes and overvoltages across insulators due to direct lightning strikes to the line, considering representative lightning current waveforms. Backflashover rates were determined using the Disruptive Effect Model. It was found that the decrease of soil resistivity and permittivity, resulting from the frequency-dependence effect, is responsible for significant decrease of the expected outage rate of the tested lines, in the range of 13-32% for usual distributions of soil resistivity along the lines.