A study on the initiation conditions of upward leaders from large-crab-windmills and the lightning protection methods

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Lightning to a windmill and its lightning-protection tower was observed in 2005, 2006 and 2007 winter seasons. All lightning recorded are upward lightning and they can be sub-classified into two types according to whether or not their initial upward leaders are preceded by discharge activities occurred in another place, such as in cloud. Wind appears to play a certain role in initiating the latter type of lightning from the tower. Without assistance of nearby lightning discharge activities and strong wind, a rotating windmill tends to have more chance to initiate an upward lightning. The lightning on the tower occurred in all directions. In contrast, the lightning on the windmill occurred either in directions far away from the tower or nearly in vertical directions. A slight difference has been noted in upward progression directions of the two sub-classified types of windmill lightning. We have also obtained evidence of upward aborted leaders that are initiated from high-grounded objects in response to nearby lightning.