Close up - Winergy's onshore/ offshore HybridDrive system

Windpower Monthly technical writer Eize de Vries talks to Winergy about its latest medium-speed drive system for onshore and offshore wind turbines.

Winergy's HybridDrive is designed for both onshore and offshore turbines
Winergy's HybridDrive is designed for both onshore and offshore turbines

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German integrated geared drive system supplier Winergy has introduced a new compact medium-speed drive system focused at geared offshore and onshore wind turbines with power ratings of 6–7MW. The technology, dubbed HybridDrive, will be first fitted into a new 3MW wind turbine from German supplier Fuhrländer.

A HybridDrive consists of a two-stage planetary gear system and a permanent magnet-type synchronous generator integrated into a single product. A power converter can supplement HybridDrive, as Winergy is likely the world's sole fully integrated wind turbine drive system supplier able to design and manufacture gearboxes, generators and converters.

This follows the introduction at Germany's Husum WindEnergy 2010 event, in September, of another major drive system innovation: a gearbox for German supplier Bard's new 6.5MW offshore wind turbine scalable up to 12MW. The main functional characteristic of this patented gearbox design is "multi-load sharing", whereby input power via a central gearwheel is redistributed to eight smaller and faster identical rotating gear sets. As a next step, rotational speed is further stepped up and redistributed to four gear sets, then finally to two high-speed output shafts.

A HybridDrive prototype unit will be applied for the first time in a new 3MW Fuhrländer FL 3000 IEC WC IIa wind turbine model with rotor diameter of 120 metres. The prototype is to be completed by next April. Development of the technology marks cooperation between German companies Winergy, Fuhrländer and wind turbine development consultancy W2E Wind to Energy.

W2E earlier developed a smaller 2.5MW Fuhrländer FL 2500 turbine model, fitted with a flanged gearbox and a non-integrated, doubly-fed induction generator. Both turbine models feature a patented "Larus Compact" drive train system, which as a main design feature transmits "pure torque" while preventing harmful rotor bending moments from entering into the gearbox.

The mechanical and dynamics department at Germany's Rostock University is also involved, while Germany's environment ministry has provided financial support for the FL 3000 product development as part of efforts to foster innovation.

A key focus of the HybridDrive's product development was compact design. A direct flange connection of the two-stage gearbox to the generator eliminates the need for an intermediate shaft. According to Winergy business development representative Tobias Hang, this enables drive train length to be shortened by about 35% compared to a conventional non-integrated geared drive system of similar power rating.

An additional focus to achieve maximum operational efficiency under both partial and peak load. Winergy claims that its total system peak efficiency of over 94% is among the best of all existing drive technologies. Also, a HybridDrive only requires about 20% of the rare earth elements for permanent magnets used in the generator, compared to a direct-drive generator of the same power rating, Hang says.

The compact HybridDrive's dimensions provide a number of benefits. There are options to substantially reduce nacelle size and thus weight, and/or to move the converter and transformer into the nacelle instead of the tower foot. A HybridDrive can also be combined with either a single rotor bearing or a main shaft with two bearings, whereas a potentially substantial nacelle mass reduction will positively impact tower and foundation mass and costs. The modular concept also enables relatively easy and straightforward individual component exchange with the aid of an inboard crane.

Finally, a clear majority of wind turbine gearboxes are equipped with roller type bearings. The HybridDrive's planetary gears can also be fitted with journal bearings. The latter combines compact dimensions with a high load carrying capacity, a built-in capability to absorb peak loads and a long service life.

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