Transient Response Analysis of Wind Turbines Exposed to Lightning Strokes

The number of wind farm installations is continuously increasing, since the early 1990s, as the wind energy is a clean source of electrical power. Wind turbine (WT) power plants are constructed at locations where wind speed exceeds the cut off value. At these locations, there is a high probability for the WT to be struck by lightning. A numerical method is proposed in this paper to determine the transient behavior of WT exposed to a lightning stroke. The work is aimed at proposing a model of WT for lightning transient analysis seeking determination of the temporal variation of the induced voltage along turbine blades, tower and grounding system. The blades of WT are simulated by a set of vertical segments. Also, the WT tower is split into a number of cylinders and each cylinder is simulated by a wire-grid composed of vertical segments. A coupled RLC network model of a WT along with the grounding system under the tower is developed to study the transient response of a WT exposed to lightning strokes. The WT grounding system is modeled by a ring supported by a set of vertical and horizontal rods following IEC 61400-24 standard. The propagation of the lightning impulse current along the blades and the tower is investigated by calculating the transient response of the RLC network through the solution of the describing circuit equations. In order to check the validity of the model, the obtained temporal variation of the induced voltage on WT components are compared and agreed reasonably with those reported in the literature. The calculated induced voltage values increase with the increase of the tower height and grounding resistance.