Flashover Probability of Wind Turbine Blade and Impact of Strong Electromagnetic Pulse from Lightning Strikes on Wind Turbine Safety

This paper systematically studies the flashover probability of wind turbine blade lightning arrester and the impact of strong electromagnetic pulses on the local and surrounding wind turbines during lightning strikes.The research results indicate that the flashover probability of direct lightning strikes by the wind turbine blade lightning arrester is almost negligible,and the strong electromagnetic pulse of wind turbine blade during lightning strikes has a serious impact on the electronic equipment of the machine,while the impact on the surrounding wind turbine is relatively small.At the same time,the calculation formula for the reflection of lightning current on the carbon brush between the wind turbine hub and the engine compartment during the flashing of the wind turbine blades is provided,and the calculation method for calculating the spatial gradient distribution of electromagnetic field intensity using Biot-Savart Law theorem is applied.The limitations of using wind turbine blades for lightning protection are pointed out,and a technical route for achieving wind turbine lightning safety is proposed,which can be used as a reference for wind turbine lightning protection technicians.

Back to school after lockdown: The effect of COVID-19 restrictions on children’s device-based physical activity metrics

Background:The coronavirus disease-2019(COVID-19) pandemic and national lockdowns took away opportunities for children to be physically active.This study aimed to determine the effect of the COVID-19 lockdown on accelerometer-assessed physical activity(PA) in children in Wales.Methods:Eight hundred participants(8-18 years old),stratified by sex,age,and socio-economic status,wore Axivity AX3 accelerometers for7 days in February 2021,during the lockdown,and in May 2021,while in school.Raw accelerometer data were processed in R-package GGIR,and cut-point data,average acceleration(AvAcc),intensity gradient,and the acceleration above which the most active X minutes are accumulated(MX) metrics were extracted.Linear mixed models were used to assess the influence of time-point,sex,age,and socioeconomic status(SES) on PA.Results:During lockdown,moderate-to-vigorous PA was 38.4±24.3 min/day;sedentary time was 849.4±196.6 min/day;mean± SD.PA levels increased significantly upon return to school(all variables p <0.001).While there were no sex differences during lockdown(p=0.233),girls engaged in significantly less moderate-to-vigorous PA than boys once back in school(p <0.001).Furthermore,boys had more favorable intensity profiles than girls(intensity gradient:p <0.001),regardless of time-point.PA levels decreased with age at both time-points;upper secondary school girls were the least active group,with an average M30 of 195.2 mg(while in school).Conclusion:The lockdown affected boys more than girls,as reflected by the disappearance of the typical sex difference in PA levels during lockdown,although these were re-established on return to school.Upper secondary school(especially girls) might need specific COVID-recovery intervention.