Fraunhofer's test bench for rotor blade bearings of up to 6.5 meters in diameter has been commissioned at the institute’s Hamburg facility, paving the way for automated continuous operation.
The accelerated tests – simulating 20 years of service in six months of testing – will enable manufacturers and operators to increase the reliability of large rolling bearings and develop new calculation methods and designs. A bearing can also be validated on the test bench long before it is installed in a wind turbine, the German institute said.
“This phase is the manifestation of the past five years of research work and we get to see how well the safety systems and the components interact,'' said Fraunhofer IWES' Senior Engineer Matthias Stammler.
The aim of the testing is to lower development costs and reduce yield loss in order to make it more economical to operate wind turbines of up to 10MW.
Failures well before the end of the calculated fatigue life are not unusual for wind turbine rolling bearings, according to Fraunhofer. At the moment, certification bodies do not require a service life calculation for such oscillating rolling bearings that connect rotor blade and rotor hub because current methods produce results with limited significance.
Given a better understanding of what is happening early on in the process of damage, designs can be modified, design methods reviewed, and the risk of failure lessened, according to the institute. Comparing simulation data with measurement data makes a detailed fatigue lifetime calculation possible. Not only the bearing as a whole but also individual sections of the raceway are calculated to get more exact figures.
The first significant test objects weigh around 9,500 kg each and are part of the HAPT (Highly Accelerated Pitch Bearing Test) research project funded by the German Federal Ministry for Economic Affairs and Energy (BMWi): eight bearings with a nominal diameter of five meters will undergo tests of function and fatigue between now and the summer of 2021. This project in collaboration with the Institute of Machine Elements, Engineering Design and Tribology (IMKT) of Leibniz University Hannover and the IMO Group aims to develop methods for the accelerated testing of rotor blade bearings.
In addition to the BEAT 6.1 large bearing test bench, the institute operates other test rigs for rotor blade bearings and main bearings as well as smaller facilities for basic experiments and for testing large quantities.
Photos: Jan Brandes/Fraunhofer