By this time next year, project partner Lindø Offshore Renewables Center (LORC) expects a new main bearing test facility (MBTF) for main shaft bearings in Odense Harbour, Denmark, to be in commercial operation.
The required total investment of nearly €40 million includes a €10 million grant from Denmark’s GreenLab programme, while the Odense Harbour authority will finance and oversee the construction of the testing hall.
Ready for today and tomorrow
Once operational, this world-leading facility aims to test and validate main bearings and main bearing arrangements well into the coming decades.
While the initial MBTF focus was on the next generation of offshore wind turbines, there is now growing interest in onshore turbines too, due to their rapid scaling, says LORC chief executive Torben Lorentzen.
“These increasingly large onshore turbines offer new potential customers for our new testing rig,” he says, adding that at LORC they often ask themselves whether the current MBTF testing capability will prove to be big enough.
“But we and our partners must accept that future predictions are not simply a matter of looking at a crystal ball for ready answers on what could or is most likely to happen,” he elaborates.
A parallel challenge is how much ahead to plan based on the available insights regarding capacity upgrades and/or a successor MBTF – including how and where to secure the required investments in good time.
Lorentzen then moves to the massive MBTF foundation, constructed and cast outdoors during the first half of this year. It required around 300 tonnes of reinforcement steel plus approximately 7,000 tonnes of concrete.
As of 26 August, pile ramming to support the testing hall to be built around the foundation (pictured below) was almost completed, with only a few more days to go.
Progress report
During our conversation on that same day, Lorentzen summarised the latest progress and timeline of the MBTF project.
“We are right on track to meet the original schedule, with commercial operation in late August next year,” he confirmed, adding that installation of the test facility’s main components and completion of the accompanying infrastructure would begin in early 2025.
“It will greatly enhance our current bench testing portfolio, including a 16MW nacelle test rig and the world’s largest at 25MW. The latter has been in commercial operation since 2021 and is fully booked until 2028.”
The 35-metre long and 18-metre high MBTF incorporates two secondary areas to prepare bearings – and bearing assemblies such as the increasingly popular main bearing units (MBUs) – for testing.
This aims to reduce transition time between two test trials and thus optimise the utilisation rate of the test rig. Lorentzen notes that, in a busy year, the test rig’s availability will be limited to a maximum of three projects (see below).
In test rig jargon, the single bearings and twin-bearing assemblies (MBU) arrangements are known as Device Under Tests (DUTs).
Thanks to its location next to LORC’s test rig facilities, the MBTF enjoys direct access to the existing physical infrastructure including a 1,200-tonne crane capable of lifting DUTs directly from vessels onto the test rig. It also benefits from the facility’s removable roof allowing easier and faster DUT changeover cycles.
Test rig development specialist
Danish test rig design specialist R&D Test Systems, which earlier developed and built LORC’s 16MW and 25MW test rigs, has been newly appointed the MBTF turnkey design and test equipment supplier/contractor.
The detailed contract package includes engineering, development, manufacturing, delivery, assembly and installation, and final commissioning of the test equipment.
After a test object (DUT) is mounted on the test rig, it is mechanically connected to a Test Load Unit (TLU). This device provides primary power for rotation and has a built-in capability to apply bending moments and forces.
This specific TLU incorporates a hydraulically activated mechanism that applies advanced load control of forces, bending moments and torque – fully independent of each other – to a given bearing unit (DUT). This allows DUTs to be validated in a matter of months by simulating their 25-year lifetime span in an actual turbine.
R&D Test Systems Key Account Manager Peter Winther explains that the TLU’s drive system comprises an electric motor with gearbox and power converter, but – in contrast to nacelle test rigs – requires only sufficient power output to overcome the internal resistance of bearings during tests.
“This MBTF is designed to accommodate both geared and direct-drive main bearing arrangements. We also made this design upgradeable, which then enables testing and the validation of new bearing technologies beyond the current 25MW-plus range,” he said, noting that he was unable to provide more details on any upgrades at this stage.
Simulating actual turbine loads
The TLU mechanism can apply loads that are similar to what a bearing ‘sees’ when it is incorporated inside an actual turbine of matching size.
It simulates five degrees of axes of freedom inherent to what real turbines experience in the field: thrust and horizontal and vertical forces, tilt moment, and yaw moment.
Winther adds that the latest TLU design builds on R&D Test Systems’ ten-year track record with LORC and additional test rig clients.
He further notes that the MBTF being built at LORC can apply bending loads in excess of 100 Mega Newton metres (MNm) to simulate a turbine’s extreme operating conditions, or to observe how failure progresses after purposely introducing a specific bearing damage. “It can also apply over 10MN thrust forces for simulating a given set of actual rotor wind loads,” he adds.
A bench testing scope should never be to make something fail catastrophically, Lorentzen explains, because these extreme event outcomes are difficult to predict and can in fact turn out to be dangerous.
Bearing solutions provider
The third MBTF development partner is German multinational Schaeffler Technologies, a bearing technology specialist and bearing solutions provider to the wind industry.
The company contributed to the joint project by defining the test rig’s specifications and signed up to become the first user of the facility.
Schaeffler’s director of application engineering for wind systems, Andreas Mangold, says the company has been using for years a comprehensive testing roadmap to ensure its product offerings to wind industry clients are competitive and robust.
He highlights a combination of product (bench) testing and fundamental research in support of his Schaeffler’s growth ambitions: “Our dual focus is the multi-megawatt future wind markets for onshore and offshore wind.”
Once this MBTF is operational, Mangold explains, Schaeffler will continue to build on the valuable insights it gained through developing bearing solutions, ever since the then world’s most powerful main bearing test rig, ‘Astraios’, started operating in 2011.
Schaeffler's older Astraios test rig
“The close cooperation with LORC, a world-leading testing facility for wind, will enable Schaeffler to advance faster into the enlarged sizes of the future. And this, in turn, contributes to the more rapid development of reliable next-generation multi-megawatt turbines,” he says.
A full bearing testing and validation run at Schaeffler’s Astraios currently takes between six and 12 months. Because overall test rig costs are the main driver, turning to shorter test cycles would by definition make it economically unviable.
Core business
Noting that roller bearings (pictured below) are Schaeffler’s core business, Mangold sheds some more light on the company’s strategic wind business roadmap: “For bearing solutions testing we will always come to LORC with an OEM client in a joint approach. In parallel, we will continue to further develop and validate software-based simulation tools building on the current successful base.”
The requirements for offshore wind are such that the Astraios device will no longer be suitable for such trials, he says.
The strategic partnership with LORC enables Schaeffler to expand on its roadmap: staying competitive, supplying mature reliable products and continuing to focus on where the limits are will remain the company’s main drivers, Mangold adds.
With fully integrated medium-speed drivetrains rapidly becoming a popular wind technology choice, especially for large-scale offshore, one key unanswered question is where to set subsystem boundaries as a key DUT parameter.
Because the main shaft output side is directly and rigidly attached to the gearbox input side via the low-speed planet carrier, a comprehensive system understanding is essential for development and validation. But the MBTF partners refrained from getting into further detail on this issue.
“Building this MBTF would be too large an investment for individual suppliers,” Lorentzen concludes. As a commercial organisation that can facilitate multiple international clients but also receives Danish government financial support, LORC demands open competition for limited places between potential MBTF test clients. “This provides equal opportunities to all”.
Image credits: Schaeffler
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