RBE – Rotor Blade Extension: consequences for individual components
Considering that the equipment is built to withstand a certain load and a certain behavior, if modifications occur in the structures, it is necessary to examine its potential effects.
In the case of Rotor Blade Extension, extensions of 1.5 meters are placed in the blades of wind turbines. How this extension can increase efforts to equipment? It is necessary to evaluate the effects of the change in the structure, especially in blade deflection, the consequences for the rotor, the implications for the foundation of the wind tower and the influence on the lifetime of the machine.
Regarding the blade deflection, an increase of approximately 350mm (30%) occurs. This is still within the original design considerations, including a safety factor of 1.5.
RBE is used at locations with overestimated wind conditions. Thus, despite the additional loads on the blades of the RBE, an additional weight of 45 kg per blade, the values are within tolerances. The blade angle control receives approximately 1-3% load increase (within the pre-established tolerances).Rotor Blade Extension installation on a hanging blade.
No critical changes were determined on both the rotor’s and the tower’s natural frequencies by implementing the RBE modification.
Due to the natural increase of the rotor thrust, because of the application of the RBE, the cut out wind speed needs to be reduced from 25 m/s to 23 m/s. Therefore the absolute highest rotor thrust available is limited to the original level. This way, the pre-defined safety is ensured.
Foundation of the wind tower
The foundation statics of the wind tower remain unchanged, despite the RBE installation, due to: unmodified rated power state; equal rotor thrust compared to the original design; small blade mass increase does not affect strain loads.Foundation of a wind turbine. Source: Erich Hau, Windkraftanlagen, Springer, 2008.
Lifetime of the machine
Regarding the fatigue of the wind turbine, there is no significant influence to its lifetime, due to less load cycles than the turbine is designed for.