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Close up - Gamesa's G128-4.5MW turbine

Windpower Monthly techical writer Eize de Vries runs the rule over Gamesa's G128-4.5MW turbine, examining features such as its segmented 128-metre rotor blades, control system and nacelle mounted crane.

At EWEC 2010 Gamesa introduced its new flagship turbine: the G128-4.5MW. The product features a number of innovations, including segmented Gamesa-design InnoBlade rotor blades and a medium-speed geared drivetrain. Equally impressive is the record 128-metre rotor diameter and a 250 tonne Top Head Mass (THM).

In late 2008 Gamesa erected a prototype at an R&D wind farm named Cabezo Negro in Spain's Saragossa region. The top priority was to commence controller testing and optimising with the company initially fitting the prototype with a provisional 107-metre rotor.

According to a Gamesa spokesperson at EWEC the larger segmented 128 metre rotor blades are going to be fitted on the prototype within weeks. The huge blades consists of a glass fibre reinforced epoxy composite inner and outer section, each less than 35m long for transport logistics reasons, and are assembled together by a bolted joint.

Eliminating potential stiffness interruption risk in the joining cross-section proved a major technological challenge said Gamesa's CTO Jose Antonio Malumbres. Currently the only commercial turbine fitted with segmented rotor blades is Enercon's 7.5 MW E-126 (rotor diameter 127m). However, unlike Gamesa, the company chose a hybrid solution comprising a 22-metre tapering steel inner blade section and a 35-metre composite outer section. 

Reliability and logistics

 The key aims behind developing the G128-4.5MW were maximum drive system reliability, and transportation and erection equipment logistics similar to the smaller 2.0MW product series.

Besides maximised drive system reliability, additional product development demands concerned optimised systems flexibility and stability, together aimed at setting new Life Cycle Costs (LCC) performance standards.

Speaking about this, Malumbres said: "Direct drive system limitations focus at complex and costly transport and erection logistics due too generator size and weight. By choosing for a medium speed drive system we could simultaneously eliminate the otherwise required trouble-prone high-speed gear stage as a reliability enhancing measure without compromising on overall systems flexibility."

The ‘CompacTrain' drivetrain system itself comprises a semi-integrated main shaft with twin bearings and a two-stage planetary-type gearbox. The rated generator speed is only 448rpm, much less compared to a conventional (~1000 - 1500) high-speed generator speed range. Equally new is a switch away from Gamesa's current double-fed induction generator solution to a permanent magnet (PM) synchronous generator with full converter.

Cyclic rotor blade pitching

A combination of Gamesa's new ‘MultiSmart' turbine control system supplemented by advanced load reducing cyclic rotor-blade pitch technology is claimed to have contributed positively to the favourable 250-tonne THM (nacelle + rotor) figure. Cyclic pitch technology continuously monitors blade root loads and readjusts the blade angle during each rotor revolution.

Another interesting feature is Gamesa's ‘FlexiFit' nacelle mounted crane system. The ground assembled self-mounting system is capable of exchanging even a complete drive system. The added feature aims at offering substantially lowering erection costs whilst achieving higher operational availability of the installations in the field.

Series production start is envisaged for 2012 with the US & Canada, Spain, Italy, Germany, France, and China pinpointed as likely markets.

 

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