Close up -- Eize de Vries examines Vestas' latest onshore products

It has been a busy year for Vestas' technology division with the company launching and evolving a number of onshore products. It has introduced two new versions of the V80/V90/V100 1.8MW series and three 2MW GridStreamer turbines. Lastly, there is the V100-2.6MW turbine model, which is based upon the V90-3.0MW. Eize de Vries spoke with Vestas Technology R&D president Finn Strøm Madsen about the company's recent activities.

The Vestas V100 2MW Gridstreamer model
The Vestas V100 2MW Gridstreamer model
The origins of Vestas' recent innovations date back to 2000 when it introduced a variable speed V80-2.0MW turbine featuring an 80-metre rotor diameter and doubly-fed induction generator [DFIG]. Following this, the V90 and V100 sister models were introduced, offering an increased 90-metre and 100-metre rotor diameters and a choice between a 1.8MW or 2MW power rating. To date, over 7,800 2MW units have been manufactured, making it one of Vestas' most popular and one of the wind industry's most-sold product series.

But the V100-1.8MW Vestas set an important trend. It was one of the first turbines with low specific-power rating — MW/m2 rotor-swept area — aimed at achieving high capacity factors at common low and medium wind-speed sites. Now Vestas seeks to target the market for grid access and behaviour-friendly low wind turbines with the latest version, the 1.8MW/2MW GridStreamer turbine.

The GridStreamer models come with similar rotor diameters to the previous versions. However, it also includes a liquid-cooled Vestas-design permanent-magnet generator (PMG) and full-power electronic converter is now fitted as standard. Another addition included is a new gearbox developed by the recent wind-turbine gearbox market entrant German automotive transmission specialist ZF, which is bidding for Hansen Transmissions of Belgium.

The turbines also use a Cooler Top cooling radiator unit first used on the V112-3.0MW. This latter feature is characterised by natural water circulation and a minimised number of moving parts.

Explaining the GridStreamer's development process, Vestas Technology R&D Finn Strøm Madsen said: "The changes were not only technological. V100-2MW GridStreamer model also moved up from IEC class IIIA to class IIA while the power rating increased from 1.8MW to 2MW. The change resulted in higher loads and increased demands on the structural strength and stiffness.

"This explains the introduction of a single cast main shaft housing with integrated bearings instead of the original two individual bearing blocks. The switch to a PMG was prompted by our belief that this contributes towards meeting future grid requirements, including wind markets with a high wind-power penetration."

Madsen added it had been Vestas' long-term design philosophy to keep the nacelle's mass as low as possible. PMG's thereby offer both superior partial-load efficiency and weigh significantly less compared to DFIG's.

Existing models will for some time continue to be offered in parallel to new GridStreamer models. This strategy is targeted at offering supply-chain synergy benefits to large existing clients with a substantial 1.8MW and/or 2MW Vestas turbine operational base.

Technically the new V100-2.6MW turbine is similar to the lightweight V90-3.0MW. It includes a compact drive system with flanged gearbox plus integrated rotor bearing and DFIG. The V100-2.6MW concept with its enlarged rotor size and reduced power rating follows common engineering up-scaling practice, and is based on the principle that power is a function of torque and RPM.

Madsen says Vestas has learned from the past in developing its turbines. In 2003 Vestas caused a sensation and set new standards by designing its V90-3.0MW product with a 104-tonne top-head mass (nacelle plus rotor). Soon afterwards serious gearbox-related issues emerged while additional design imperfections had to be addressed as well. In 2007, Vestas withdrew the V90-3.0MW from the offshore wind market for one year.

Besides at least five gearbox retrofits, additional main technical modifications involved a yaw motor number increase from four to six and reinforcing the main chassis structure. Nacelle mass increased to 111 tonnes.

Recalling that unfortunate period, Madsen said that this was not an easy decision but that Vestas wanted to be in control while resolving the gearbox issue: "In close cooperation with our gearbox suppliers we found and implemented a final solution, which created a sound base for platform continuation and expansion. Customers also responded positively and we believe that it in fact positively impacted our reputation in the market."

With the V100-2.6MW, Vestas focuses on the market for IEC WC II wind turbines with over 2MW power rating, including sites with megawatt and/or tip height restriction.

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