Lightning strike is one of the most serious damages to the wind turbine blade. The blade is in rotation when lightning strike happens. The influence of the rotation to the lightning attachment manner of wind turbine blade is not fully studied. Experimental work has been done in this paper. A 1:30 scale 3MW wind turbine is built. There are 3 side receptors on each blade according to the real wind turbine blade. A rod electrode is used as the high voltage electrode to simulate the downward leader. Both negative and positive 250/25000μs standard switching impulses are applied. Different blade tip linear speeds, equal to the real wind turbine, are used to study the influence of the blade rotation to attachment process. The results show that the influence of the rotation can be classified into two types, one is the impact on the location of the striking attachment point, the other is the impact on the discharge channel close to the blade. The influence depends on the polarity of the discharge. Positive discharge is more dangerous to wind turbine blade in rotation.

It is not clear for the damage mechanism of the blade structure under the effect of the lightning strike arc. In this paper, the damage characteristics of blades under the effect of lightning arc are obtained by the impulse large current experiment. Based on the actual blade structure, An MHD (magnetohydrodynamics) model is built suitable for multi-field coupling of heat-magnetic-airflow and we obtain the temporal and spatial variation of the temperature and pressure. The experimental results show that the blade tends to crack from the position of the trailing edge near the arc attachment point and the crack extends in the direction of the blade root and tip. The length of carbonization damage caused by high temperature of arc is much smaller than the crack length due to the airflow impact. When the down-conductor is placed on the main beam, carbonization damage distributes in the area between the left web and the trailing edge. When placed on the right web, it distributes between the right web and the trailing edge. In the finite element simulation, the temperature of the arc ignited point increases to the peak value and then decreases rapidly and then, it increases to the maximum and tend to stabilize. The high temperature inside the blade region diffuses from the boundary between the pressure surface and the right web to the trailing edge. The pressure of trailing edge increases to the maximum and then oscillates to decrease. The airflow inside the blade continuously oscillates between the right web and the trailing edge. It is recommended to improve the toughness of epoxy resin adhesive and set the down-conductor on the main beam.

Lightning accidents seriously threaten safe operation of the wind turbines due to unclear initiation mechanism of the airborne lightning induced discharges on turbine blades, in which turbine rotation is one of the principal influencing factors. To study the impact mechanism of wind turbine rotation on corona discharge inception, a numerical model with dynamic meshing of charged ions in the neighboring space of large-scale rotating wind turbine during thunderstorm was established in this paper, and the validity of the model was verified by long gap discharge experiments on a scaled wind turbine. Based on the proposed model, the spatial and temporal distribution of charged particles in the neighboring area of the rotating wind turbine as well as the space charge-caused local electric field distortion scenario were obtained. The influence mechanism of blade rotation on corona discharge inception was further analyzed and elucidated accordingly. The results indicate that, the charged particles are unevenly distributed near the rotating blade tip, and the contours present a strip-like shape, the critical area of which may facilitate corona discharge inception. As the blade speed increases from 6rpm to 20rpm, the E-field extremum at the blade tip increases by 38%, causing the blade tip prone to initiate corona discharge. The critical rotating speeds corresponding to corona inception probability were calculated under different thunderclouds-determined field strengths and a safe boundary was defined, by which it is recommended that wind turbines operate at a reduced speed below 8rpm under thunderclouds conditions. Index Terms-Wind turbine, rotating blade, ion flow distribution, charge density descent vector, corona discharge I. INTRODUCTIONN recent years, wind power generation has developed on a large scale worldwide. According to the statistical data from Global Wind Energy Council (GWEC), the new installations surpassed 90GW in 2020, among which China's new wind power capacity accounted for 56%; at the end of 2020, the global cumulative wind power capacity was up to 707GW, and

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Lightning accidents seriously threaten safe operation of wind turbines because the influence mechanisms of wind turbine rotation on corona and upward leader initiation are, so far, not clear. A three-dimensional stochastic evolution model of the lightning downward leader was established by combining the dielectric breakdown model and the lightning current shunt method, according to which the charge density distribution of leader branches was determined. The corona and leader initiation mechanisms of rotating wind turbine were studied based on the 3D drift and diffusion model of ion flow in the neighboring space of a rotating wind turbine. The results show that due to blade rotation, the charged particles are unevenly distributed near the blade tip and the contours are in a strip-like shape. As the rotating speed increases, the blade tip is more susceptible to initiating corona discharge. Combining the three-dimensional stochastic development model of the lightning downward leader and ion distribution model near a rotating wind turbine, the initiation direction of the upward leader was analyzed, and in 66% of cases, the initiation direction of the upward leader on the blade tip was on the back side of the blade rotation.