Modern Wind Turbines adjust their blades orientation at different wind speeds for power control and optimum energy production. A big slewing ring about 2 metres diameter placed at each blade root, allows the blade orientation withstanding highly variable heavy loads, vibrations, continuous rotating oscillations and severe ambient conditions. The blade pitch system design and control strategy in a WTG is strongly conditioned by the load dependant friction of the bearing that shall be accurately defined for cost-effective designs. The pitch system is also the main brake of the rotor requiring high reliability for their components under fatigue loads, and in particular for the slewing rings due to its inherent difficulties for maintenance or replacement. The present methodology allows the fatigue and friction estimation of slewing rings, based on rolling bearing models and classical theories like Hertz, Lundberg-Palmgren, and Miner fatigue cumulative damage. This approach simulates the stress supported by each ball in the contact with the raceways, estimates the bearing friction due to these contact stresses, and the fatigue life of the overall bearing.

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