In this paper, a long-term fatigue damage analysis method for gear tooth root bending in wind turbine's drivetrains is presented. The proposed method is established based on the ISO gear design codes which are basically developed for gears in general applications, not specifically for wind turbine gears. The ISO procedure is adapted and further improved to include the long-term fatigue damage of wind turbine's gears. The load duration distribution (LDD) method is used to obtain the short-term stress cycles from the input load time series of global response analysis. Dynamic loads and load effects in the gearbox are obtained by two dynamic models; a simplified approach and Multi Body Simulation (MBS) method. A good agreement between these two methods is observed. The long-term fatigue damage is then calculated based on the SN-curve approach by considering all short-term damages and the long-term wind speed distribution. Finally, the reliability and service life probability of failure considering load and load effect uncertainties is calculated. The procedure is exemplified by a 5 MW gearbox designed for a pitch controlled, bottom-fixed offshore wind turbine.

This paper presents detailed descriptions, modelling parameters and technical data of a 5 MW high speed gearbox developed for the National Renewable Energy Laboratory (NREL) offshore 5 MW baseline wind turbine. The main aim of this article is to support the concept studies and researches for large offshore wind turbines by providing a baseline gearbox model with detailed modelling parameters. This baseline gearbox follows the most conventional design types of those used in wind turbines. The gearbox consists of three stages, two planetary and one parallel stage gears. The gear ratios among the stages are calculated in a way to obtain the minimum gearbox weight. The gearbox components are designed and selected based on the offshore wind turbine design codes and validated by comparison with the data available from the manufacturer of large offshore wind turbine prototypes. All parameters required to establish the dynamic model of the gearbox are then provided. Moreover, a maintenance map indicating components with high to low probability of failure is shown. The 5 MW reference gearbox can be used as a baseline for research on wind turbine gearboxes and comparison studies. It can also be employed in global analysis tools to represent a more realistic model of gearbox in the coupled analysis.

No abstract