Transient Analysis on Wind Farms with Interconnected Grounding Systems Located on Frequency-Dependent Soils

This paper investigates the transient voltages generated in a wind farm located on frequency-dependent (FD) soil for lightning striking at one of the towers. The soil is modeled by its FD electrical parameters proposed by CIGRE WG. First,‘ the ground potential rise (GPR) and voltages at different parts of the wind turbine are calculated using commercial full-wave electromagnetic software XGSLab
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employing the numerical Partial Element Equivalent Circuit (PEEC). The wind farm is formed by four wind turbines with a grounding system interconnected by underground cables buried in soils with FD electrical parameters and four values of resistivity are assumed: 500, 1,000, 3,000 and 5,$000 \Omega$.m. The time-domain voltages are calculated for a 50-kA lightning current representative of the subsequent negative impulse modeled by Heidler’s function. Results have demonstrated that voltage peaks increase significantly with the increase in soil resistivity increases. When the wind structures are considered, multiple reflections of the surge waves from the tower base provoke oscillatory behavior at the voltage waveforms, being more oscillations found when the soil resistivity decreases. The voltages peaks at the tip of the blade and the nacelle have shown no significant variation during the transient state, however, a notable difference is observed at the steady state.