Transient Analysis on Wind Turbines above Frequency-Dependent Stratified Soils

Abstract

Wind turbines (WT) due to their height and locations on high isokeraunic areas are frequently exposed to lightning strikes. To properly investigate the lightning performance of the WT, the ground must be modeled by its frequency-dependent (FD) soil electrical parameters (resistivity and permittivity) with variable water content whose soil is structured as a stratified medium. In this article, the transient voltages on the WT located on umid stratified FD soil are calculated and compared with those computed by the frequency-constant (FC) soil model. First, the harmonic grounding impedance is computed for a frequency range from 100 Hz up to 5 MHz and the Ground Potential Rise (GPR) developed for the first and subsequent return strokes are assessed for three configurations of soil. The temporal voltages generated on the tip of the blade and tower base are computed for these lightning currents. Simulation results indicated that the voltages are significantly reduced when stratified FD soil models are employed. Concerning the WT, the voltages at the injection point have presented no expressive impact for both soils. However, the voltages developed for both lightning currents at the base of the WT have a pronounced difference, especially for homogeneous high-resistive soils.