Comparison of soil modeling concerning physical factors: Application to transient analysis in wind turbines

Abstract

This work analyzes the impact of the physical factors (frequency effect, water content, and porosity level) on the voltages developed along the wind turbine (WT) subjected to lightning strikes. The analysis is performed considering a realistic grounding system (GS) where the full-wave electromagnetic (ES) software FEKO/Altair Engineering® calculates the GS harmonic impedance (HI) for 100Hz to 10 MHz. For this purpose, six soil models [Visacro–Portela, Portela, Visacro–Alípio, Alípio–Visacro, Datsios–Mikropoulos, and Archie] and their transient responses are assessed. Comparisons are made with those assuming a frequency-constant (FC) soil at the dry condition. The GPR on the GS and the voltages on the tower base and nacelle are calculated using the software ATP® for the transient analysis. Results show a significant impact on HI with the physical factors, being remarkable at high frequencies and for high-resistive soils. Consequently, a notable decrease in the GPR peaks is seen compared with those with FC soils. These soil models and the lightning currents influence voltages at the nacelle and tower base. Results demonstrated that the Portela model predicts a more significant decrease in the voltages, and Datsios-Mikropoulos’s model provides closer responses to the FC soil. Increasing porosity yields larger peak values, and increasing water content produces lower voltages.