Static and Fatigue Strength Analyses of Low-speed Shaft in a 2.5 MW Wind Turbine

The low-speed or main shaft of wind turbine transmits the rotary motion and torque moments of rotor to gearbox. This component works under rotational dynamic loads and hence, its fatigue life is crucial. This part is a massive part usually made of forged or cast iron. Reducing the main-shaft weight can lead to several tons reduction in complete nacelle mass. In this study, static and fatigue analyses of the low-speed hollow shaft of a 2.5 MW wind turbine have been performed. This shaft is of a special shape with a short length (673 mm) and low weight (≈ 2 tons). The shaft is constructed from spheroidal cast iron EN-GJS-400-18U-LT which is a semiductile material. Therefore, either the maximum principal stress hypothesis or the maximum shear strain energy hypothesis (e.g. von Mises) can be applied as equivalent stress hypothesis in the static analysis. In static analysis, it is observed that main shaft could withstand extreme load without failure. In preload step, bolt holes have subjected to plastic deformation around the edge. For the fatigue analysis of main shaft, two methods have been used: damage equivalent load range (DEL), and the rain flow count of fatigue loads (RFC). From fatigue analysis, as the damage sum may not exceed unity, it is concluded that the main shaft can withstand the fatigue loads.