The rolling bearings for rotor shaft bearing arrangements are subjected to highly dynamic loads and operating conditions. Schaeffler develops solutions for rotor bearing arrangements for all modern wind turbine variants from 220 kW up to the current multi-megawatt class.
The different concepts range from the classic 3-point shaft bearing arrangement and hub bearing arrangement up to the 2-point shaft bearing arrangement or single bearing concept. To further increase reliability, all bearing types and bearing concepts used in the drive shaft can be tested on the new large-size bearing test stand Astraios. This allows further improvements in the understanding of systems as a whole, influencing factors and the interrelations in the drive trains of wind turbines.
Moment bearing arrangements in all designs
With the trend towards large multi-megawatt turbines, that are used particularly in offshore wind farms, single bearing concepts in particular are gaining importance. With this concept, the rotor is only supported by a single double-row tapered roller bearing – a so-called moment bearing – in an O arrangement that supports all forces and moments. This single bearing concept can take different forms, for example, with a shaft and gearbox as well as a high-speed generator, as a hybrid solution with shortened gearbox and medium-speed generator or as a direct drive without a gearbox.
The moment bearing arrangements that are individually designed for the respective turbine type are available from Schaeffler with two cage variants: the classic, highly robust steel pin cage or a reduced-friction plastic segment cage, which also enables optimisation of the lubricant supply with low wear characteristics and low weight.
E1 spherical roller bearing X-life with steel cage
For medium-sized wind turbines with outputs from 1.4 to 2.1 megawatts, Schaeffler supplies the FAG E1 spherical roller bearing as the classic bearing variant for the rotor main shaft in wind turbines. Typical bearing sizes are are also available with steel cage instead of the conventional solid brass cage. The steel cage is split and, as a result, is ideal for applications in wind turbines. The cage halves can rotate at different speeds if alternating or unequal loads are applied to the two rows of rolling elements. This puts less strain on the cage.
Furthermore, the surfaces are hardened, which also increases the wear resistance. The high-strength steel used allows the cage to be designed with a very thin wall thickness. Overall, the steel cage occupies only around one third of the volume taken up by a conventional solid brass cage. This means more space remains in the rolling bearing for the lubricant and the distribution of the lubricant is also improved.
The overall bearing operating life is increased as a result. All FAG E1 spherical roller bearings are designed in X life quality, with increased robustness and load carrying capacity, less friction and increased efficiency, as well as a longer operating life. The design measures lead on average to a 50 percent higher limiting speed and allow the dynamic load rating to be increased by 15 percent.
In addition, all spherical roller bearings are offered with black oxide coated rolling elements. Schaeffler has developed the coating system Durotect ® B for this purpose. The coating, which is just 0.4 to 2 µm thick, minimises the risk of slippage-related damage, improves running-in behaviour and, not least, provides protection against corrosion.
Large-size bearing test stand tests all concepts for rotor bearing arrangements
With the commissioning of the largest and most powerful large-size bearing test stand in the world, Schaeffler has continued to expand its technological leadership in wind power applications. This unique test stand allows large-size bearings weighing up to 15 tons and with outside diameters of 3.5 metres, as used in wind power applications in particular, to be tested under realistic conditions using a comprehensive simulation program.
This means Schaeffler is making a major contribution to shortening development times for wind turbines as well as making the design process more reliable and increasing the cost-effectiveness and safety of these turbines for customers. At around seven million euros, the Schaeffler large-size bearing test stand is a significant investment in the further development of renewable energies.
Schaeffler Wind Power Standard (WPOS)
Schaeffler has introduced a new Wind Power Standard (WPOS) for its INA and FAG brand bearings for wind power applications, which fulfils the increasing demands in terms of reliability placed on wind turbines and components in the wind power sector.
This new standard for products and processes means Schaeffler is ensuring outstanding quality and reliability. All bearings for wind power applications will be included in this new wind power standard by the beginning of 2014 and will also be labelled with the WPOS designation.
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Press release, September 21, 2012; Image: Schaeffler