Effects of Blade Extension on Power Production and Ultimate Loads of Wind Turbines

Blade extension is an important type of technical transformation to improve the energy production of turbines for early-built wind farms. To evaluate the effects of blade extension on wind turbines, a 1.5 MW commercial wind turbine with three 37.5 m long blades is taken as the research object; the power enhancement and the load variations are systemically evaluated for three different blade extension lengths (1 m, 1.5 m and 2 m) resorting to the software GH-Bladed. The load cases cover all the requirements of the IEC-61400-1 standard. It is found that the optimum tip-speed ratio λopt and the corresponding power coefficient CPmax increase with the blade extension length. The annual energy power production is enhanced by about 3%, 4% and 6% for the extension length of 1 m, 1.5 m and 2 m, respectively. The steady loads and dynamic loads, especially the thrust force of the rotor, the flapwise moment of the blade root and the overturning moment at the tower bottom, are significantly enhanced as the improvement of the power. In particular, the percentage increase of these quantities are over 10% when the extension achieves 2 m. It is also shown that blade extension can produce good economic benefit and the benefit improves with the extension length within the safety margin. The paper provides an important reference for this type of technical transformation.