Rolling bearings key to renewable energy systems

Rolling bearings are a core component of wind turbines and are key to reducing operator costs. The design of low friction bearings for a wind turbine rotor shaft and gearbox, for example, are important considerations, as well as the associated lubrication methods for the bearings, mounting, maintenance and the use of remote condition monitoring and diagnosis techniques to ensure that maintenance costs are minimised and service life is increased. In a typical wind turbine drive train, rolling bearings are used to support the rotor, alternator and gearbox. Plain bearings are found in blade adjusters in pitch-controlled wind turbines and in geared motors that drive the tower slewing ring and pitch control. Over the next decade, the significance of rolling bearings will increase as new, larger, multi-Megawatt class wind turbines are developed. This trend towards larger, multi-megawatt wind turbines will lead to more radical changes in the design of the bearings such as 'single bearing' designs. With single bearings, the wind turbine rotor is supported only by a single, double row tapered roller bearing, typically in a back-to-back arrangement that supports all forces and moments. This concept can take many different forms, for example, with a shaft and gearbox and a high-speed generator, as a hybrid solution with shortened gearbox and medium-speed generator, or as a direct drive without a gearbox. Single bearings always result in more compact designs. For example, the wind turbine nacelle can be fully integrated with the bearing-gearbox-generator unit. This means that it is possible to eliminate drive train components and reduce weight. This in turn reduces the head weight of the wind turbine, allowing smaller foundations to be used and simplifying logistics. Another advantage of the single bearing design is that preloaded tapered roller bearings can be utilised, which prevent axial clearance and small axial misalignments. This narrow, tight guidance of the rotor shaft means that less movements act on the system, reducing the negative effects on the gearbox and generator. Dr Steve Lacey, Engineering Manager, Schaeffler (UK) Ltd