Single-bearing designs customised for wind turbines

By using its in-house advanced rolling bearing calculation software BEARINX, in combination with finite element analysis (FEA) tools and multi-body simulation (MBS) models, Schaeffler's engineers can assist customers during the initial stages of wind turbine design. This helps to improve the reliability and efficiency of the turbine under a wide variety of load conditions. Schaeffler is able to develop bearing designs that are tailored to specific wind turbine requirements, including turbines for both onshore and offshore wind farms.

This powerful combination of software enables Schaeffler to evaluate various load conditions and to assess accurately all relevant, critical load conditions for wind turbines. The use of 'moment' bearings in single-bearing designs enables a high level of system integration, resulting in extremely compact, less complex wind turbine designs. The preloaded bearing also prevents the transfer of negative axial loads to the wind turbine drive train.

The trend towards large, multi-megawatt wind turbines, particularly in offshore wind farms, has led to a change in the design of bearings for wind turbines. Single-bearing designs are becoming increasingly important.

Double-row tapered roller bearing

With single bearings, the wind turbine rotor is supported only by a single, double-row tapered roller bearing or 'moment' bearing, typically in a back-to-back arrangement to support 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 arrangement with shortened gearbox and medium-speed generator, or as a direct drive without a gearbox.

Single bearings 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, enabling smaller foundations to be used and logistics to be simplified.

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 controlled guidance of the rotor shaft means that fewer movements act on the system, which reduces the negative effects on the gearbox and generator.

Software enhancements

Schaeffler has already implemented numerous single-bearing designs for customers, including 5MW offshore wind turbines. To engineer bearing variants for applications such as these is particularly challenging, as standard software tools cannot be used for the design and calculation of the bearing rating life. Schaeffler has therefore expanded BEARINX to include elasticity effects, which are calculated using finite element methods (FEM). BEARINX can now analyse bearings including the influences of housings. Around 250 classified load cases are evaluated, taking all elasticities into account, resulting in an optimal design that considers almost every conceivable critical load condition.

The results of the FEM calculations for the housing are transferred to a 'rigidity matrix' and entered into the BEARINX calculation. This matrix represents not only the elasticities at individual bearing positions, but also the influences of the elasticities from one bearing position to another. BEARINX is therefore able to perform complete rating life calculations based on the load distribution and elasticities. Schaeffler says this means it has a unique calculation tool for designing rotor bearings for multi-megawatt turbines.

Schaeffler supplies moment bearings that are individually designed to match the respective turbine. These bearings are supplied with classic steel pin cages or with PEEK segmented cages that reduce friction and increase the efficiency of the turbine. This cage also improves the guidance of the rolling elements, while optimising lubricant supply.

Moment bearings can also be supplied with integrated anti-corrosion protection, which is achieved by applying a zinc flame-sprayed surface coating and multi-layer painting. Special hardening processes enable custom material characteristics for integrated functions such as seals or connections to adjacent structures.

For more information about Schaeffler's bearings for wind, tidal and wave energy systems, contact the marketing department on +44 (0)121 313 5870 or email [email protected].