Main bearings are the heart of every rotor in wind turbines. They play a central role in the efficiency of the overall system and must, therefore, pass extensive tests. To ensure that these high requirements are met by main bearings, Liebherr-Components has constructed a new main bearing test bench at its site in Biberach an der Riss (Germany). "With this test bench, we are at the forefront of technology in the wind energy sector. We make a decisive contribution to a cleaner and more sustainable energy supply," explains Andreas Palmer, head of slewing bearing development and design. "We have already been testing and validating main bearings in-house since 2017. The new and larger main bearing test bench enables us to put bearings with a diameter of up to six meters through their paces, and thus move into completely new dimensions."
Testing makes the difference
The new main bearing test bench has a maximum electrical drive power of 300 kW and a maximum bearing speed of 15 rpm. This allows it to accommodate an impressive test weight of up to 125 tons. The test bench is used to carry out a variety of tests, including functional testing of the bearing, checking the lubrication and sealing system and recording the bearing frictional torques as a function of load and operating constellations. Part of the test programme is also the determination of the total bearing service life under specific operating conditions, as well as the bearing heat balance for various operating points.
To perform these tests, two bearings are always required – a test bearing and a counter bearing. The test load is generated by plate weights or hydraulic cylinders, while an electric motor rotates the bearings. "To test a main bearing, we calculate the load on that bearing for a life of, say, six months. The main bearing is then run at overload to simulate the stress it is put under during a lifecycle of 25 years," explains Andreas Palmer. "With these tests, we validate our calculation method, among other things, in order to be able to determine the correct raceway geometry already in the design of such bearings."
The result matters
Inspections and tests are important, because they do not only validate main bearings, but also uncover development opportunities. "This is how, for example, the demand for our superfinish for main bearings came about," continues Andreas Palmer. The superfinish refines the raceway surface. In this process, the surface is rotationally machined, so that the raceway forms an almost mirror-smooth surface. Tribology, i.e. wear, friction and lubrication, are thus optimised. As a result, superfinish ensures high surface quality and increases service life.
Always onward, always forward
"Since 2015, we have been delivering main bearings for wind turbines at Liebherr-Components. Thanks to our new test bench, we are currently able to validate a main bearing for an 11 MW turbine," Andreas Palmer summarises. "Thus, with this test bench, we are optimally positioned for the conditions of the market and further growth in turbine size."
