Frequency Domain Analysis of a Wind Turbine Generator Earthing System for Lightning Discharge currents

A safe and cost-effective design of a wind turbine generator (WTG) grounding system requires accurate modeling of local soil resistivity, particularly when wind turbines are spatially distributed across a wide area with different soil types and features. In this paper, three locations at an Australian wind farm were modeled based on measured data. Four soil resistivity models were considered: uniform, multi-layer horizontal, vertical, and exponential variation with depth. Full-wave electromagnetic simulations were performed at different lightning discharge current frequencies to find the expected ground potential rise and WTG earthing impedance in the event of a lightning strike. Furthermore, the effect of frequency dependent soil parameters on the WTG earthing was analyzed, along with the effect of foundation rebar on the grounding impedance. Our results show that an accurate soil resistivity model is critical in the design of a WTG earthing system.