Two-Layer Earth Modeling Approaches for Electromagnetic Transient Analysis of Overhead Lines

Soil stratification significantly affects the electromagnetic transient (EMT) responses of overhead transmission lines (OHTLs) under lightning strikes. Rigorous two-layer models offer high accuracy but involve complex semi-infinite integrals. Equivalent homogeneous earth models (EHEMs) are commonly used to reduce complexity. This article investigates the impact of different soil modeling approaches on the lightning-induced transient behavior of single-circuit OHTLs. The analysis involves a generalized two-layer soil model, two EHEMs and a homogeneous soil model using the bottom and upper layer resistivity. Simulations are performed under multiple lightning current waveforms, varying line lengths, and two representative soils cases. Results in both time- and frequency-domain show that soil resistivity and line length significantly affect the voltage magnitudes and the related resonance frequencies. The study concludes that to ensure reliable EMT simulations—particularly for short lines—it is essential to use an accurate earth modeling approach.