Transient Model of Grounding System Considering Soil Ionization and Frequency-Dependent Electrical Parameters

Lightning strikes are a leading cause of power outages in transmission systems. Evaluating the transient response of grounding systems is critical for effective lightning protection. This response is governed by both soil ionization and frequency-dependent properties. Previous studies often faced challenges in accurately modeling soil ionization and validations limited to experimental currents featuring either short wavefronts or high amplitudes. This paper proposes a transient model for a grid-type grounding system that accounts for both soil ionization and frequency-dependent effects, solved using a Fourier transform-based time-frequency domain transformation method. By integrating layered soil modeling with an electric field-dependent soil ionization model, the approach significantly enhances computational accuracy. The model is validated under triggered lightning conditions considering a soil resistivity of 230 Ω·m, and effectively addresses both short wavefronts and high-amplitude currents, with model predictions deviating from measurements by only 3.5%.