Observation of an upward lightning flash with 21 upward positive leaders initiated from different wind turbines in wind farm

As the wind turbine height increases, the probability of multiple upward leaders flashes within the wind farm increases. In this study, an upward lightning flash containing 21 upward positive leaders (UPLs) initiated from different wind turbines in Zhangbei Wind Farm was analysed. The average speed of the UPLs was 1.2 x 10(5) m/s, which mostly decreased to zero before reaching the cloud height. Only four UPLs developed to cloud height, with prolonged periods of bright light on three of them and with a minimum duration of 126 ms. A total of nine return strokes occurred on the other two dissipated leader channels, and the numbers of strokes on the two channels was six and three, respectively. The average interstroke interval for the return strokes was 10.5 ms. Most of these nine return strokes had peak currents smaller than 10 kA. The high-speed video frames confirmed that competition does exist between the UPLs, and the range of shielding effects increases as the height of the ULs increases. The effect of fan rotation on the initiation of upward leaders and the shielding effect between the wind turbines and upward leaders are discussed.