In the HAPT research project (short for Highly Accelerated Pitch Bearing Test) researchers from the Fraunhofer Institute for Wind Energy and Energy System Technology IWES and the Institute of Machine Elements, Engineering Design and Tribology (IMKT) at Leibniz University of Hanover work together with the IMO group to establish the foundations for the further development of blade bearings. It is also aimed that the project results will allow the use of individual pitch control systems for load reduction – a primary goal of the manufacturers. The German Federal Ministry for Economic Affairs and Energy (BMWi) provided funding for the project to the tune of € 10.7 million.
In wind turbines in the 7-10 MW range, the wind drives blades of up to 80 m in length. Blade bearings, the interface between the hub and the blades, are the design bottleneck in the development of systems of this size. Due to the sheer dimensions of the blades, the systems are subject to effects which can be already detected in turbines with smaller dimensions but are not all that significant.
As the load increases, faults in the blade bearings also increase exponentially and the rate of damage rises. At the same time, almost no information is available on how and why these faults develop. As a result, experience-based design of blade bearings, standard practice among manufacturers, is now reaching its limits.
One possibility for reducing the loads to which the structure of the wind turbines is subject is individual pitch control (IPC), which balances out the loads across the individual blades and reduces them overall. However, as there is still no reliable information available concerning the suitability of blade bearings for the use of IPC and because the latter further increases the demands placed on the blade bearings, the industry sector remains somewhat hesitant to introduce this seminal technology.
The researchers involved in the HAPT project want to resolve these uncertainties by developing a test bench for blade bearings and a method for calculating their service life. Accelerated testing procedures should make it possible to simulate 20 years of operation in a testing period of just six months.
“According to our strategy we contribute method expertise of testing wind turbine components,” comments deputy director Prof. Dr. Jan Wenske the IWES’ share. The aim is to provide the industry with the necessary prerequisites for the computational design of blade bearings – dimensioning will become more precise, the use of IPC will be made reliably possible and levelized cost of electricity will be cut at the same time.
IMO Head of Engineering Hubertus Frank is confident: “The new testing opportunities of HAPT will establish a new basis for the development of future blade bearings. We will provide blade bearings and a wealth of practical know-how for the tests.” Prof. Dr.-Ing. Gerhard Poll of the Leibniz Universität Hannover sees beneficial effects:
“I expect this project to bring together the competencies of Fraunhofer IWES, Leibniz Universität Hannover - and thereby ForWind - in an exemplary way. Along with IMO Group the wind turbine technology will make a big step forward.” The results of the project will be incorporated in the future standardisation of blade bearings.
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The IMO Group was founded 1988 and has more than 25 years experience in designing, manufacturing and supplying slewing rings and self-contained slew drives. Currently more than 500 employees work for IMO worldwide. IMO ball and roller slewing rings are being designed, manufactured and sold in diameters 100 mm up to more than 6000 mm in a wide variety. Applications include for instance industrial and plant building, cranes, construction machinery, mining and medical technology. In renewable energies IMO is a leading supplier of blade, yaw and main bearings for on- and offshore wind turbines, and provides blade bearings for tidal stream systems. IMO Slew drives are used in manlift platforms, tunneling, steering equipment such as gantry cranes and heavy-duty transporters, cranes or many more.
Babette Dunker | Fraunhofer Institut für Windenergie und Energiesystemtechnik IWES
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