Upward Lightning Attachment Analysis on Wind Turbines and Correlated Current Parameters

Abstract

This work provides insight in the attachment characteristics of upward initiated lightning discharges to wind turbines and their possible consequences for the lightning protection of wind turbine blades. All discharges were recorded at the Japanese coast of the Sea of Japan which is known for intense upward lightning activity. 172 video recordings of lightning discharges on rotating wind turbines are analysed and attachment angle, detachment angle, and the resulting angular displacement were determined. A classification between self-initiated and other-triggered upward lightning events is performed by means of video analysis. The results reveal that the majority of discharges are initiated when the wind turbine blade is aligned vertically; however, also lightning attachments to horizontal blades are reported. Horizontal attachment (or a slightly inclined blade state) is often related with a triggered lightning event prior to the discharge. There are about twice as many lightning attachments during the ascending blade movement compared to the descending blade movement. Furthermore, a comparison between current parameters of upward lightning flashes during stationary and rotating wind turbine operation reveal no substantial difference between the two operational states.