Wind turbines (WTs) are one of the most promising sources of sustainable energy. However, they are frequently subjected to lightning strikes resulting in downtime of WTs and loss of numerous megawatts of power generation. Studying the transient behavior of a WT when two blades are struck simultaneously by lightning is the main contribution of this paper. Although the simultaneous hitting of two blades of the same WT is not occurring frequently, it is more severe than striking a single blade. Hence, assessing the transient behavior of WTs during this phenomenon is important for proper lightning protection system design. The variation of induced overvoltages across the WT during the strike is calculated using a simplified numerical model. The equivalent circuit of WT is represented in the time-domain, including various WT parts starting from the blades up to the grounding system. Then, the continuous time-domain circuit is converted to a discrete time-domain circuit, and the system nodal equations are written to calculate the transient response. For checking the validity of the numerical model, a small-scale WT model is connected with an impulse generator to simulate the lightning strike in the laboratory. The measured overvoltages across the small-scale WT are found to be very close to the numerical ones at different grounding resistances, which proves the correctness of the numerical model. |
