Impact of Grounding System Modeling on Overvoltage Waveforms for Direct Lightning Strikes at Wind Turbines

Wind farms represent a fundamental component of the worldwide transition to renewable energy. However, wind turbines are exposed to lightning strikes due to their tall structures. In this context, adequate modeling of wind turbines is essential to determine the generated overvoltages during a lightning strike. One of the key parts of the wind turbine is the grounding system, where lightning current must be dissipated into the soil, ensuring that a safe earth potential is maintained. This paper investigates distinct grounding system models and their impact on the generated overvoltages in the nacelle and tower base when a wind turbine is struck by lightning. The analysis is performed considering a realistic wind turbine grounding system (WTGS) using the full-wave electromagnetic FEKO/Altair Engineering® to calculate its harmonic impedance for the frequency range 100 Hz to 10 MHz. Based on this impedance, the low-frequency resistance RLF and the impulse impedance Zp are computed. Soilsrepresented by four distinct values of low-frequency resistivity ρ0 are assumed: 500, 1,000, 2,500 and 5,000 Ω · m. The software ATP-EMTP® is used for the circuit model of the wind turbineand numerical simulations. Results demonstrated that significant differences can be obtained for the GPR and overvoltage waveforms at the nacelle and tower base, where the use of RLF tends to underestimate the transient responses whilst Zp is a more adequate and concise representation of the grounding system.