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Husum Trade Fair: Systems streamlined to perfection

Wind energy suppliers at the Husum WindEnergy trade fair are continuously optimising technology to lower energy costs. Larger rotors, as well as concept design, are fast becoming a main wind industry trend.

The bulkiest items on the floor at the biennial wind event are usually gearboxes, generators, castings, main shafts and bearings. At this year's event in Husum, Germany, Swiss technology group Ruag outdid the others, displaying a mammoth full-scale model of its 3MW medium-speed concept wind turbine, upon which the firm will base technology development. Made of plywood and sheet metal, it sparked keen interest.

Main features include a compact fully integrated, geared CIRRDrive system and nacelle mass of about 75 tonnes. The planned generator has a rated speed of 200 rotations per minute, which would rank it at the low end of the speed range. The mass specs would compare well with those of the 3MW lightweight Vestas V90-3.0MW turbine and Siemens' SWT-3.0-101 direct-drive turbine models. There was also strong interest in Vestas's V112-3.0MW scale-model. Germany's Avantis Energy and South Korean firms Unison and Hyosung - a newcomer to manufacturing wind turbines - presented their products in this manner as well.

Germany's Vensys Energy and its major shareholder Goldwind, of China, together presented a new 2.5MW lightweight direct-drive turbine at Husum. The turbine is available with a choice of 90-metre and 100-metre rotors. Goldwind has said over 2,000 units of its mainly 1.5MW direct-drive turbine have now been installed. Vensys developed the technology. Smaller Chinese suppliers present at Husum were Guodian United Power Technology, which showed off a 3MW model, and Sany, which displayed geared 1.5MW and 2MW models, and a 3MW model for offshore application.

A 2.7MW direct-drive turbine prototype was presented by Schuler, a German specialist supplier of automotive production technology. Despite being a newcomer, the company's wind turbine drew attention for its distinctly streamlined design. Schuler is also reported to be developing a 6.5MW offshore turbine.

Meantime, Gamesa of Spain introduced its new 2MW G97-2.0MW model. It features a 97-metre rotor diameter designed for Class IIIA low winds. Until now, the largest rotor diameter on this model was 93 metres. Fitting increasingly larger rotors on wind turbines of a given power rating has become a main wind industry trend.

Described as continuous product evolution, GE Energy introduced two up-rated product families. First is a 1.6MW version of the proven 1.5MW workhorse. The new model is fitted with a GE generator and either 82.5-metre or 100-metre rotor diameters.

Also new is a 2.75MW version of the 2.5MW 2.5-100 model, which will initially be offered with 100-metre and 103-metre rotor diameters. From 2012, GE will fit a new 112-metre rotor based on its Aero-elastically Tailored (AT) rotor blade design. It is distinguished by a slender load-reducing rotor blade with a double bend.

The company is field-testing AT prototype rotor blades on a GE 2.5MW turbine in the Netherlands. Comprising a 110-metre rotor diameter, these blades will also be fitted on GE's 4MW 4.0-110 direct-drive offshore turbine. For the German market, GE has introduced modular hybrid concrete-steel towers with hub heights up to 140 metres.

Service

Repower Systems of Germany presented a new service that it claims is able to provide service and maintenance for up to 240 turbines a year. It uses a custom-developed jack-up vessel - a mobile platform able to stabilise itself on the sea floor - and two dedicated support ships. The self-propelled jack-up vessel will be permanently stationed at large future wind farms from 2013, is fitted with a 500-tonne crane and accommodates 90 service staff.

As for its onshore business, Repower displayed its new 3.2M114 turbine, with a rotor diameter of 114 metres, designed for lowand medium-wind-speed sites.

German engineering consultancy Aerodyn has a long history of developing turbines for third-party clients. One of these is a 5MW Bard offshore turbine. In 2007 Aerodyn presented a full-scale model of a 2.5-3MW Super Compact Drive (SCD) wind turbine concept, on display at Husum that year. Since then, they have developed the technology and established a subsidiary also called SCD. SCD's technology builds on patented Multibrid hybrid technology that Aerodyn developed in the mid-1990s (see box, previous page).

This September, Chinese Aerodyn licensee Mingyang erected a 3MW two-blade prototype north of Shanghai, and a second fully instrumented prototype is planned for October. A 6.5MW two-blade downwind prototype with 140-metre rotor diameter and a combined nacelle and rotor mass of only 205 tonnes is planned for installation next summer in China.

Also at Husum, German gearbox supplier Winergy displayed a massive gearbox with two generator output shafts developed for Bard Engineering's new 6.5MW offshore turbine. The gearbox is scaleable up to 12MW. One characteristic of the patented gearbox design is "multi-load sharing", in which the wind's power is first transmitted into the turbine's gearbox via a low-speed shaft connected to a central gear wheel. The energy is redistributed to eight smaller gear sets that rotate much more quickly. It is further stepped up and redistributed to four gear sets, and finally to two high-speed output shafts each driving a separate generator.

The reason for fitting two fast-speed 3.25MW generators is practical, as the largest available standard synchronous generator size is 5MW, too small for Bard's 6.5MW turbine. Higher capacity non-standard synchronous generators have to be engineered, so the Winergy solution also allows Bard to exploit standard generator design today. Winergy spokesperson Tobias Hang says the gearbox design that internally splits and redistributes power enables a one-third increase in power rating by retaining a similar weight to Winergy's conventional 5MW gearbox.

Flexibility

Two additional Bard 6.5 prototypes will be fitted with a medium-speed Jahnel Kestermann gearbox and a Voith Turbo hydrodynamic WinDrive system. WinDrive enables both variable-speed turbine operation and fixed-speed generator operation. This allows direct connection of the generator to the grid at either the European frequency of 50Hz or 60Hz in the US by eliminating an electronic power converter that would otherwise be required. An additional benefit of the fixed-speed synchronous generator system is that, since it resembles a conventional power station arrangement, all future grid integration requirements can be met.

At a Husum press conference, power engineering giant ABB said it expects the main focus of the future offshore market to be simplicity and reliability of wind turbine systems. It also expects a majority of future turbines to be fitted with permanent-magnet generators (PMGs) with full converters. Also, it believes turbines 5MW and above will be equipped with medium-voltage technology, usually defined as 1-38kV.

During the same presentation, ABB showed figures indicating that the magnets in direct-drive PMG turbines contain about ten times more rare-earth materials than high-speed systems of similar power ratings. The requirement could become a key driver for drive system technology if, for political reasons, future availability of crucial rare-earth materials tightens. China's recent blocking of exports of rare-earth metal to Japan sends a chilling signal.

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