However, the reliability of the Haliade™ 150-6MW turbine is largely the outcome of a whole series of innovations. “Instead of adapting onshore technology to offshore requirements, the Haliade™ was completely designed from scratch,” Castell stresses. A prime example is the direct-drive permanent magnet generator. Here, to improve the performance of the large structure, the magnets have been located in the rotor and the windings in the stator only. This makes the generator simpler, lighter, more robust and more reliable, compared to traditional solutions with windings in both the stator and the rotor. “This solution is new to offshore wind turbines,” adds Castell.
The direct drive approach is also an innovative wind turbine solution. In conventional wind turbine designs, the generator speed is high and a gearbox is used to step up the shaft speed. “But a gearbox has lots of components such as bearings and gears that make the installation heavier, less reliable and more expensive to service,” Castell points out. In contrast, with direct drive the generator is directly attached to the turbine rotor. This means that the generator’s rotational speed is the same as the blade’s rotational speed. It also means that the generator itself is much larger, but it is robust enough to withstand the forces exerted on it and still make the overall installation lighter.
It captures more wind and produces more energy per turn with a lighter solution.
A key feature of the direct drive permanent magnet generator is its failure tolerance, thanks to having 3 independent generation lines; failure in one line does not affect the others, and operation can continue at de-rated output.
Thanks to the larger rotor diameter, it is estimated that the Haliade™ 150-6MW will show an annual energy production rate 15 % higher than the current generation of large turbines. The blades themselves are unique. At 73.5 metres in length, these blades are the largest ever manufactured for a wind turbine (the previous record was 12 metres less) and are almost as long as the total wingspan of an Airbus A380. In fact, the full diameter, at 150 metres, is longer even than a standard football field. As a result, it captures more wind and produces more energy per turn with a lighter solution, optimising the yield-mass ratio (MWh per tonne of head mass). “However, with such huge dimensions, we decided to locate assembly operations close to the shore – as close as possible to the final location – to minimise transport issues.”
Robust, reliable and high-performance – PURE TORQUE®
The robustness and performance of the Haliade™ 150-6MW offshore wind turbine is due to a great extent to the innovative electromechanical layout that combines Alstom’s rotor support technology with a direct drive permanent magnet generator, resulting in the superior reliability of the turbine’s single-flange drive train structure that produces and transmits the electricity. The fluctuating forces and changing directions of the wind in offshore installations could be detrimental to the drive train.
The ALSTOM PURE TORQUE® feature protects the generator and improves its performance by diverting unwanted stresses from the wind safely to the turbine’s tower through the main frame. This design, which is already available in Alstom’s onshore turbines, separates the turbine rotor and generator. Two solid bearings transmit the main bending loads to the tower, while a flexible coupling ensures that the generator rotor receives only the turning force, the torque. This allows the minimum sufficient air gap to be maintained between the generator rotor and stator at all times, producing maximum electrical efficiency.
The ALSTOM PURE TORQUE® feature