Experimental study on lightning attachment manner to rotation wind turbine blade

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

Numerical study on explosion characteristics of wind turbine blade under lightning induced arc

For enhancing the lightning protection abilities of wind turbine blades, there is the need to study the mechanical explosion characteristics when the blades suffer from lightning induced arc intrusion. In this paper, a magnetohydrodynamic (MHD) model of lightning induced arc intrusion into the blade was developed, and the airflow and gas pressure distribution were calculated accordingly. The simulation results show that the huge pressure generated at the trailing edge of the blade should be the main cause of the trailing edge cracking. The research presented in this paper provides a theoretical basis for improving the structural design of the blade from the lightning protection perspective

Thundercloud induced spatial ion flow in the neighborhood of rotating wind turbine and impact mechanism on corona inception

Lightning accidents seriously threaten the safe operation of wind turbines due to the 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 the dynamic meshing of charged ions in the neighboring space of a large-scale rotating wind turbine during a thunderstorm was established in this article, 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 distributions of charged particles in the neighboring area of the rotating wind turbine and 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 6 to 20 rpm, 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 thundercloud-determined field strengths, and a safe boundary was defined, by which it is recommended that wind turbines operate at a reduced speed below 8 rpm under thundercloud conditions

The influence of the metal mesh to the attachment manner of CFRP wind turbine blades

Wind turbine blade with carbon fiber reinforced plastics (CFRP) beam has much better mechanism performance. However, it faces the severe problem of lightning protection due to the conductivity of CFRP. Metal mesh are installed on CFRP blades by many manufacturers in order to protect the main beam. The performance of the metal mesh was not fully tested with real blade tip. In this paper, the blade tip equipped with tip receptor and fully covered mesh are tested under both negative and positive switching impulses. The results show that the mesh has little influence on the attachment manner. The results between none-mesh GFRP and with-mesh CFRP blade is also compared

A quantitative evaluation method for failure risk of the lightning attachment system on wind turbine

The lightning damage seriously affects the normal operation of wind turbines, but there is currently few quantitative analysis methods for the failure risk of the lightning attachment system on wind turbine. Based on leader development model, this paper proposes the definition and calculation method of the lightning shielding failure rate (LSFR) of the lightning attachment system on wind turbine. Taken into the influence of the blade orientation, the LSFR of the blades regarding different lightning attachment systems were comparatively analyzed. The proposed assessment method can provide a theoretical basis for the optimal design and failure risk assessment of the lightning attachment system on wind turbines

Damage mechanism of wind turbine blade under the impact of lightning induced arcs

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 an lightning arc are obtained by the impulse large current experiment. Based on the actual blade structure, a magnetohydrodynamics model is built to be suitable for multifield coupling of the 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 the high temperature of the 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 tends 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 the 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 the epoxy resin adhesive and set the down-conductor on the main beam

Experimental study on interception efficiency of receptor on wind turbine blade with brine adhesion

Lightning creates a huge threat to offshore wind turbine due to its height and the marine environment. The blade surface will be polluted by brine after long operation in highsalinity and high-humidity environment. In order to study the efficiency of the receptor under the influence of brine covered on blade surface, a group controlled test is conducted in this paper. Statistical analysis is applied according to the test results. The results show that, the adhesion of brine on the blade surface reduces the interception efficiency of receptor greatly, which makes the blade exposed to a huge threat of lightning damage. Only water or salt has limited impact compared with brine. The influence of the brine area is more obvious if the area is close to the receptor. It can expand the severe area of strike and reduce the interception efficiency of the receptor. The brine area far from the receptor has a limited effect on attracting downward leader

Dietary fiber intake and non-alcoholic fatty liver disease: The mediating role of obesity

Background and aimsDietary pattern rich in fiber is negatively associated with the risk of non-alcoholic fatty liver disease (NAFLD). Meanwhile, obesity is a known predisposing factor for NAFLD. Nutrient-focused research can enhance the mechanistic understanding of dietary effects. We thus hypothesized that higher dietary fiber intake was associated with lower risk of NAFLD through the mediating role of obesity.MethodsIn this nationwide cross-sectional study, dietary fiber was surveyed using two 24-h recalls. NAFLD and clinically significant fibrosis (CSF) were determined by vibration-controlled transient elastography. Multivariable logistic and linear regression were applied to investigate the association of dietary fiber with NAFLD, CSF, and liver function parameters. We used counterfactual-based mediation analysis to estimate the direct and indirect effect of dietary fiber on NAFLD.ResultsOf the 3,974 participants, ~36.86% and 7.78% of participants were diagnosed with NAFLD and CSF. Compared with participants among the lowest tertile, the highest tertile of dietary fiber consumption was associated with lower odds of NAFLD (OR = 0.81; 95% CI: 0.66–0.98; Poverall = 0.019). Dietary fiber intake appeared to be linked with lower odds of CSF (ORTertile3vs.Tertile1 = 0.81; 95% CI: 0.58–1.14; Poverall = 0.107). Mediation analysis showed that obesity fully mediated the association of dietary fiber with NAFLD. Dietary fiber was associated with improved hepatic parameters.ConclusionsThe findings indicated that increasing dietary fiber intake could confer a greater benefit to protect against NAFLD. Translating these findings regarding dietary fiber into dietary advice might be an attractive strategy for NAFLD prevention

Numerical Simulation of the Lightning Leader Development and Upward Leader Initiation for Rotating Wind Turbine

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

Numerical simulation of the lightning leader development and upward leader initiation for rotating wind turbine

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