Experimental evaluation of strategies for wind turbine farm-wide fatigue damage estimation

Abstract

A significant percentage of the existing wind turbines are reaching their theoretical design life. Therefore, important decisions about decommissioning or life extension will have to be made soon. Direct measurement of strains allows estimating the accumulated fatigue damage with good accuracy over the monitoring period, but these are still rare in this industry. As this paper demonstrates, this can be used for estimation of the damage prior to and after the measurement period. Furthermore, considering that similar wind turbines of the same wind farm have similar behaviour, the damage results can be extrapolated to the entire wind farm. In this work, the strain measurements on an onshore wind turbine over two years are used to evaluate the fatigue progression over time. The experimentally evaluated fatigue damage is analyzed against operational and environmental conditions and clustered into several load cases. Then, the damage values are stored in a database according to the corresponding environmental conditions. Based on this and on the variables that characterize operating conditions recorded since the wind farm installation, it is possible to probabilistically predict the fatigue consumption in the entire wind farm. Alternative approaches to estimate fatigue damage for non-monitored operating conditions are proposed and evaluated. The obtained results are an important step to demonstrated the feasibility of farm-wide fatigue assessment with limited additional instrumentation.