Impact of Soil Modeling on Lightning-Induced Transients in Mixed Overhead–Underground Transmission Lines

This study analyzes the impact of soil behavior on the transient responses of mixed overhead–underground transmission systems subjected to lightning strikes at the transition tower. When more realistic earth-return parameters are included in transmission lines—accounting for imperfect and frequency-dependent soil properties—the simulations reveal notable differences in the amplitude and attenuation of overvoltages on cable sheaths. Simplified soil models tend to overestimate these responses, which can result in overly conservative or misleading evaluations. In contrast, rigorous soil representations reduce the estimated energy stress on sheath voltage limiters (SVLs), particularly in high-resistivity soils. Despite these differences, the critical current threshold for cable sheath insulation failure remains nearly unchanged. The results underscore the importance of accurate soil modeling to ensure reliable insulation coordination and optimal dimensioning of SVLs in mixed transmission systems.