Reliability Analysis of Wind Turbine Towers

Abstract

To increase energy density in order to meet increasing electricity demands, increasingly large-scale designs for wind turbines have been developed. Wind turbine towers of larger sizes can generate more electricity, but such large sizes also create higher costs in terms of development and maintenance. The present research sets up a wind turbine tower model, wherein the loads of towers are calculated by their relation to wind speed. The finite element method is used to analyze the stress distribution of towers under these loads. Impacts from different loads are compared as well. The wind speed distribution is derived from data collected in Penghu, Taiwan using statistical methods. Fatigue analysis of towers is then conducted using fatigue loads and wind speed distribution, and the mean time to failure (MTTF) of towers is calculated with quantitative reliability theory. The results show that the main loads of towers are the wind force acting on the rotation area of wind turbine blades and the moment caused by non-uniform wind speed. After comparing this research finding with loads calculated by a wind turbine design software, it is concluded that it is a feasible and conservative method to analyze a wind turbine tower structure with the loads calculated by its relation to wind speed. In addition, it is shown that both the average and maximum hourly wind speeds in Penghu can be fitted into Weibull distribution. In conclusion, the fatigue analysis shows that the probability is greater than 99.8% for the tower model's failure time to be above 331,416 cycles, and it further shows that the tower model in this research possesses appropriate fatigue durability and is considered a safe tower design for Penghu.