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Windfarms are every day increasing in number. So wind turbines are an easy aim for cloud-to-ground lightning for two main reasons: high isokeraunic level over windfarm locations and the height and sharp of the wind turbine structure and blades. Then the turbine should facility current flowing through its main parts: blades, rotor brushes and tower without dangerous overvoltages. Grounding should be design to derive current efficiently, but in many situations grounding is conditioned to particular location aspects such as: extension and soil resistivity. Both aspects are strongly related with grounding performance. This paper presents an analysis of a wind turbine overvoltages. It is modelled as a transmission line with different grounding models: a constant resistance, a nonlinear model based on soil ionisation, and a windfarm interconnected grounding model. Besides not only first lightning return strokes current are considered if not, subsequent return stroke current is included too.

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