Schweinfurt, Germany — After a design and construction phase of less than two years, Schaeffler officially put the world’s largest, most up-to-date and most powerful large-size bearing test stand into operation at its Schweinfurt plant on in November 2011. The test stand enables large-size bearings of up to 15 tons and measuring up to 3.5 metres — such as those used in wind power applications in particular — to be tested in realistic conditions using a comprehensive simulation program.
The availability of this equipment 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. At around €7 million, the Schaeffler large-size bearing test stand is a significant investment in the further development of renewable energies and the company’s development location in Schweinfurt.
The new test stand will primarily be used for testing rotor bearing supports for wind turbines in the multi-megawatt class and will result in further improvements in the understanding of systems as a whole, influencing factors and the interrelations in the drive trains of wind turbines. This will result in bearings characterized by lower friction and increased design safety.
In addition, the tests will provide information about and recommendations for wind turbine operation and maintenance as well as for optimum adjacent constructions. The test stand has been named Astraios, after a Titan in Greek mythology who was father of the four wind gods.
For Maria-Elisabeth Schaeffler, partner in the Schaeffler Group, the test stand symbolizes both the immense tasks facing us in the future and the core values of the company: “For Schaeffler, this large-size bearing test stand represents a consistent step towards further strengthening the strategic growth area that renewable energies represent”, Mrs. Schaeffler said.
Setup and function of the large-size bearing test stand
The test stand carries out realistic simulations of static and dynamic forces and torque that act on the rotor bearings and slewing rings, for example. All rotor bearing support concepts for wind turbines with an output of up to 6 megawatts can be tested on the test stand. Functional tests provide insights into the rolling bearing kinematics, temperature and friction behavior, loads and deformation. The data required for these tests is supplied by more than 300 sensors on and in the bearings.
The loading frame is the test stand’s most important component. Four radial and four axial hydraulic cylinders are fixed to the frame, which generate the real loads and moments that occur in a wind turbine. The radial cylinders simulate the weight of a rotor hub with rotor blades while the axial cylinders generate the wind loads.
The rotors and hub in large turbines can weigh well over 100 tons. This weight acts on the bearing and generates a so-called static radial load and a static nodding moment. Accordingly, the four radial cylinders have impressive dimensions, since each cylinder can generate a maximum of one meganewton of force, which is equivalent to 100 tons of weight.
The axial cylinders have even more power, since they can provide up to 1.5 meganewtons for simulating the static axial load as well as the dynamic nodding and yawing moments. This nodding and yawing is comparable to the lifting and lowering and turning of the nacelle.
Various wind speeds can be simulated using the drive train and planetary gearbox. Typical speeds are between four and 20 revolutions per minute and significantly higher speeds are also possible. The tensioning frame represents the connection side of the wind turbine’s nacelle. It’s a well-known fact that the wind seldom blows at the same speed or from the same direction. In fact, it acts with varying intensity and at different points on the wind turbine. Varying moments are generated on the rotor hub, depending on the position of the rotating rotor blades. If, for example, the wind acts on the top or bottom of the rotor blades, it generates the so-called dynamic nodding moment. This is supplemented by so-called dynamic yawing moment if the wind turns and blows more strongly from the side.
These factors all mean that wind turbines are subject to extremely complex conditions due to the continuously changing wind conditions. This is a Herculean task, not only for the test stand and the eight hydraulic cylinders that simulate all real loads and moment, but also for SARA, that automatically controls the comprehensive measurement, open loop and closed loop control processes (SARA stands for Schaeffler Automation System for Research & Development Applications). SARA generates the target values in accordance with the wind loads, controls the highly-dynamic servo cylinders, controls all units, ensures all data is measured and stored, is responsible for telemetric bearing measuring technology, displays all target, actual and limit values, evaluates measured data, and generates logs.
Astraios to receive award in November 2012
Since its announcement, in February 2012, the Astraios large-size bearing test rig has become a prize winner in the competition “365 landmarks in the land of ideas” and is one of the “locations selected in 2012”. The nation-branding initiative “Germany – Land of Ideas,” an initiative of the German Federal Government and the Federation of German Industry (BDI) under the auspices of the Federal President, awards 365 outstanding projects and ideas each year, which make a significant contribution to Germany’s future viability.
As one of the prize winners in 2012, Schaeffler represents Germany’s capacity to generate innovations in a special way with its new Astraios large-size bearing test rig. The award ceremony will take place on November 7, 2012 in Schweinfurt.
“This award is another example of Schaeffler’s outstanding innovative force and shows that we are making a significant contribution to the further development of renewable energies with our investment in the new large-size bearing test rig at our development location here in Schweinfurt”, said Dr. Arbogast Grunau, president of product development at Schaeffler Group Industrial.
In addition to winning the award as a “selected landmark,” Schaeffler is also amongst the prize winners nominated in the “Environment” category as a winner at Federal level. The jury nominates one winner at Federal level for each category from the 365 “Selected Landmarks”. These landmarks are shining examples of the quality of the ideas and projects in the competition and Germany’s innovative force. 18 of the “landmarks selected in 2012” were nominated for this additional award, which will be presented in September 2012.