Electrostatic Field and Lightning Zoning analysis of a windmill: Study of current and innovative protection strategies

This paper presents the study of the electrostatic field distribution around a windmill in order to determine preferential lightning attachment zones (zoning) [1]. Whether existing studies on wind turbines often propose to use the rolling sphere method [2] more recent models based on the physics of attachment have also been applied in aeronautics [3] or on ground infrastructures as windmills [4,5]. This study is based on the positive leader inception model [6] and calculations have been performed with the ASERIS-Zoning finites elements code, which is composed of an electrostatic solver integrating a ground plane model and a probabilistic Zoning post-treatment. First, a preliminary analysis on electrostatic variations at ground level induced by different charge distributions typical of thunderclouds has been developed in order to both validate the ground plane model used herein but also to better understand the electrical field distribution that would experiment a typical windmill. After that, a relative comparison of the electric field on different lightning protection configurations has been developed in order to understand the local behaviour of the field on the surroundings of the tip of the blade. An additional electrostatic analysis is devoted to explore the local relative variations of the electric field near the tip of the blades upon the descent of a downward leader modeled as a local charge. Finally, the zoning analysis is extended to the study of the whole windmill upon full rotation of the blades. Moreover, the zoning study is also performed on current an innovative receptors as a winglet geometry that is proposed and analyzed.