A Comparison of Frequency-Dependent Soil Models: Electromagnetic Transient Analysis of Overhead Transmission Lines Using Modal Decomposition

Abstract

This article investigates the influence of four causal frequency-dependent (FD) soil models and their impact on the responses of a multiphase overhead transmission line (OHTL) with ground wires, generated by a lightning strike. The FD models proposed by Longmire-Smith (LS), Messier (M), Portela (P) and Alípio-Visacro (AV) are considered. The ground-return impedance and admittance matrices are computed with the Nagakawa approach for both frequency-constant and FD soil models. The frequency-domain modal voltages and time-domain transient voltages are assessed in this work. Modal decomposition technique is used to study the attenuation constant, propagation velocity and voltages for each propagation mode. Simulations are carried out in a frequency range of 100 Hz to 10 MHz, for OHTLs with lengths of 1 and 10 km, on soils of 700 and 4000 Ω·m. Simulation results demonstrated that the Portela (P) model has resulted in more significant variation in the ground-return impedance and admittance, constant attenuation and propagation velocity in which a pronounced variation, especially at the high frequencies, is seen. On the other hand, Longmire-Smith (LS) and Messier (M) have produced similar results in both frequency and time domains. Additionally, the Alípio-Visacro (AV) model has produced intermediate responses, being the model recommended by CIGRÈ WG C4.33. Time-domain induced voltage waveforms obtained with the Portela (P) model has shown pronounced differences, especially at the peak values, for the high-resistive soil. This study demonstrates the importance of considering the FD soil models to assess the transient responses adequately, especially when OHTLs are on high-resistive soils.

Modeling and Simulation of Distribution Networks under Lightning Transients: A Comparative Study of Accuracy and Complexity

“…Modeling these cables during transient periods is challenging, as it involves frequency-dependent distributed parameters. The choice of modeling domain (modal or phase) further complicates the calculations [27]. Overvoltage calculations require precise steps, including line parameter calculation, synthesis of model parameters, and transient solution determination [28].…”

“…For this representation, the variation of soil parameters is taken into consideration when there is a change in frequency, as groundings behave as impedances. Therefore, based on the considerations made by the studies [27,40], which present the characteristics of the hybrid electromagnetic model (HEM), it is noted that this model, based on field and circuit theories, accurately represents the behavior from DC to a couple of megahertz and takes into account the frequency-dependent soil electrical parameters. Therefore, based on the observed behaviors, this model will be implemented through a library in ATPDraw.…”