Reducing the levelized cost of electricity remains a major challenge facing the wind power industry. Schaeffler’s highly reliable and cost-effective bearing supports play an important part in making this possible. At the WindEnergy 2018, Schaeffler will be displaying innovative products with an extended operating life and integrated sensor technology as well as digital services for optimized wind turbine operation.

Wind turbines’ functionality and performance capability are decisively influenced by their bearing supports (the gearbox and especially the main bearings), as these support all of the loads that occur. Their reliability and cost-effectiveness also play an important role when it comes to the levelized cost of electricity. For this reason, Schaeffler is continuously developing optimized, innovative products that make bearing supports – and thus wind turbines – stronger and capable of supporting greater loads. This firstly involves optimizing proven solutions in terms of design to improve their power density and robustness and to simplify the relevant mounting and maintenance processes. Secondly, Schaeffler integrates sensor technology into bearing supports in order to make operating conditions and their effect on the bearing supports in operation transparent. Using the data gathered in the field allows Schaeffler to make its bearing expertise available to operators, which enables them to plan maintenance work in a predictive and requirement-based manner and make adjustments to their turbines’ operating strategies.

At this year’s WindEnergy trade show in Hamburg, Schaeffler will be presenting new and optimized bearing supports, smart components and systems for Industry 4.0 solutions, digital services, and a new test procedure.

Asymmetric FAG spherical roller bearings: Series available in X-life quality

Since the initial introduction of asymmetric FAG spherical roller bearings for main rotor bearing supports in 2015, these bearings have found application in numerous wind turbines and a complete range had been developed that fulfills the X-life standard. The asymmetric bearing design allows a larger contact angle to be used on the rolling element row subject to axial loads and a smaller contact angle on the row subject mainly to radial loads. This optimized load distribution corresponds to the typical load profile for rotor bearing supports and allows the width of the bearing to be reduced. Thanks to this bearing design, the wind turbine manufacturer can thus downsize the drive train while maintaining the same performance capability or, alternatively, increase the turbines’ performance or rotor diameter while maintaining the same bearing size. Wind turbine operators can benefit from increased turbine robustness by installing asymmetric bearings as replacement parts. Further performance enhancements can be achieved through the use of Schaeffler coating systems like Durotect B, which provides a further increase in robustness, and Triondur, which provides optimized wear protection.

4.0 solution package: Rotor bearing system with requirement-based sensors

Real operating data on the condition of the bearings offer immense potential for improving the drive train’s rolling bearing supports and the system as a whole, as well as optimizing the wind turbine’s operation. Evaluating and interpreting the gathered data makes it possible to more accurately define and if necessary reduce safety factors, for example. Schaeffler works with its customers to develop sensor concepts that allow relevant damage mechanisms for bearings to be recorded. For example, Schaeffler has developed the LoadSense Pin for specific parameters whose monitoring offers the operator added value but is not as yet carried out during operation: In the case of pre-assembled rotor bearing systems that are flange-mounted directly to the adjacent construction, the preload of the screw connections that are used partially determines the bearing’s load distribution and thus has a direct effect on its performance capability and operating life. With the LoadSense Pin, Schaeffler can monitor the preload of the flange bearing’s screw connection during operation, which allows the screws to be tightened when required and eliminates the need for the preload to be inspected at fixed intervals. This increases the reliability of the bearing system and reduces the maintenance costs at the same time.

Condition analysis via cloud-to-cloud communication

Schaeffler and ZF use jointly developed expert models to analyze and predict the condition of wind turbine gearboxes based on the actual loads that occur during operation. The data, which are generated by ZF and analyzed by Schaeffler, are exchanged via cloud-to-cloud communication. This allows ZF to integrate the bearing experts’ knowledge into its analytics-based pro-active maintenance and spare parts management. In the initial stage, Schaeffler is delivering bearing fatigue and static load safety factor evaluations for the individual gearbox bearings.

Robustness test for rotor bearings

With its realistic load simulation, Schaeffler’s proprietary large-size bearing test rig ASTRAIOS has been providing valuable results since 2011, which are used for the new development of bearing solutions and for the optimization of simulation and calculation models. Schaeffler has now developed a robustness test based on this unique long-term experience in testing rotor bearing supports for multi-megawatt wind turbines. While the fatigue life is also the basis for the design of rotor bearing supports in the wind power industry, it is less relevant when it comes to the actual bearing operating life, since other failure mechanisms often occur beforehand. The focus of the robustness test is therefore on those failure mechanisms and load conditions during operation that cannot be categorized as conventional fatigue life. The load cases in the robustness test are selected, compressed, and applied to the bearing support being tested in such a way that they represent the occurrences, loads, and stresses from 20 to 25 years of wind turbine operation in just a few months, while illustrating the specific dynamics of rotor bearing support loads at the same time. This application-specific, realistic test allows Schaeffler to achieve a level of design reliability for its customers that is higher than the current worldwide standard.

Robust against WEC: Schaeffler’s recommendation proves itself once again

So-called “white etching cracks” (WEC) are a phenomenon that has a negative influence on the reliability of bearings in wind turbines. These are structural changes in the material that form below the bearing raceway. Schaeffler is able to reproduce WEC damage on its test rigs and to derive suitable countermeasures on the basis of the results.

To efficiently and cost-effectively reduce WEC damage, Schaeffler recommends that bearings be through hardened and their rings and rolling elements coated with Durotect B. Since 2005, Schaeffler has produced and delivered one million bearings with black oxide or Durotect B coating for bearing positions that are subject to a risk of WEC, less than 0.01 percent of which have experienced WEC damage.