How does the selection of a specific yaw bearing preload affect yaw system performance and longevity, considering both static and dynamic loading conditions?

The selection of a specific yaw bearing preload significantly affects yaw system performance and longevity under both static and dynamic loading conditions, requiring a carefully balanced approach. Yaw bearing preload refers to the axial force applied to a yaw bearing during installation. This force ensures that the rolling elements (balls or rollers) maintain contact with the raceways (inner and outer rings) even under external loads. Static loading conditions refer to loads that are constant or slowly varying, such as the weight of the nacelle and rotor. Dynamic loading conditions refer to loads that are rapidly changing, such as those caused by wind gusts and turbine yawing motions. A high preload increases the stiffness of the yaw bearing, meaning it resists deformation under load. This improved stiffness reduces nacelle movement and improves the accuracy of yaw positioning, leading to better wind tracking and increased power capture. High preload also reduces the risk of slippage between the rolling elements and raceways. Slippage can cause wear and damage to the bearing surfaces, shortening its lifespan. However, excessive preload can have detrimental effects. It increases the friction within the bearing, leading to higher operating temperatures. Elevated temperatures accelerate lubricant degradation and can cause thermal damage to the bearing components. Excessive preload also increases the stress on the rolling elements and raceways, accelerating fatigue damage and shortening bearing life. For example, if the preload is too high and a strong wind gust pushes against the turbine, the combined stresses can exceed the bearing's load capacity, leading to immediate damage. A low preload, on the other hand, can lead to different problems. While it reduces friction and stress, it can also result in excessive bearing clearance. This increased clearance allows the rolling elements to move more freely, which can lead to increased vibration and noise. Low preload also makes the bearing more susceptible to slippage under dynamic loads. During rapid yawing motions, the inertia of the nacelle can cause the bearing to unload, leading to slippage and wear. The optimal preload is a compromise between these competing factors. It depends on the bearing type, size, operating speed, load, and temperature. Bearing manufacturers provide recommendations for preload based on these factors. Proper preload is typically achieved by precisely tightening the bolts that hold the bearing in place. Specialized tools and techniques are used to measure the preload and ensure that it is within the specified range. In summary, selecting the correct yaw bearing preload is crucial for optimizing yaw system performance and longevity. It requires a careful consideration of both static and dynamic loading conditions and a precise installation process to achieve the desired preload value.