Alava, Spain [RenewableEnergyWorld.com] Late in 2008 Spainish-based Gamesa put up a prototype of a medium-speed 4.5-MW wind turbine at Cabezo Negro, an R&D wind farm in the Saragossa region of Spain. Among its many innovative concepts, the main design features are segmented composite Gamesa-designed INNOBLADE rotor blades, a record 128-meter rotor size and a 250-tonne Top Head Mass (THM).
Gamesa’s key technical and marketing experts recently spoke with RenewableEnergyWorld.com about product development of the 4.5-MW turbine, major challenges and achievements and how the company plans to win new markets and increase market share.
Gamesa G10X-4.5MW is the result of a major multiyear in-house development effort, which involved more than 150 Gamesa engineers and other experts working in close cooperation with external specialists and research organizations.
If you look at the company’s product development history, it becomes obvious that this new turbine represents a huge leap forward in both rated capacity and rotor size. Gamesa’s current turbine is its 2-MW G8X-2.0MW, which has been commercially available since 2002. The G8X-2.0MW features a conventional fast-speed drive system including a multi-stage gearbox and a double-fed generator and various rotor diameters that range from 80 – 90 meters.
Reliability and Logistics
In developing the Gamesa G10X-4.5MW, the company wanted maximum drive system reliability and the ability to use the same type of transportation and erection equipment that the smaller Gamesa G8X-2.0MW series uses.
With regard to reliability, the company zeroed in on the medium-speed drive system after performing extensive multiyear drivetrain studies and development process studies that looked at many solutions. When conducting the study, the company analyzed everything from direct drive (no gearbox) solutions, to medium-speed and conventional high-speed geared solutions. In addition to striving for maximum reliability, developers also wanted system flexibility and stability, with the goal of setting new standards for Life Cycle Costs (LCC) performance, according to Gamesa CTO Jose Antonio Malumbres and others (see note below).
According to Malumbres, the company feels that the limitations associated with main direct-drive systems, “include complex and costly transport and erection logistics due to annular generator size and weight.” He said that, “by choosing for a medium-speed drive system we were able to overcome size and weight issues linked to direct drive. Simultaneously a medium-speed drive system eliminates the trouble-prone high-speed gear stage, which is integral part of three-stage gearboxes applied in conventional geared wind turbines.”
He said that by eliminating the high-speed gear stage “as a reliability enhancing measure, it proved not necessary to compromise on overall systems flexibility.”
Compact Drive
The Gamesa G10X-4.5MW CompacTrain drivetrain is comprised of a main shaft with two main bearings and a two-stage planetary-type gearbox with 1 to 37 speed-up ratio together built as a single module. Gamesa, like some of its competitors (i.e. GE and Vestas) that have also introduced new products, made a switch away from a double-fed generator to a permanent magnet (PM) type synchronous generator.
Malumbres said, “PM generators offer multiple advantages including greater compactness, slip-rings elimination, superior partial-load efficiency, and easier compliance with stringent future grid codes. Being a full converter technology it also offers greater project developer application flexibility at combined 50Hz and 60Hz wind markets.”
The generator itself is flanged directly to the gearbox and — as a self-aligning solution — virtually eliminates misalignment risks. The complete drive system is also easy to remove if it becomes necessary to split it into separate main components, he said.
The full converter system consists of modular units located in the nacelle rear and is subdivided into two levels. A medium-voltage transformer is also fitted in the nacelle rear and behind the converter, whereas a liquid-cooling system for converter, generator and gearbox is put above the converter. (See main image, top of page.)
Cyclic Rotor Blade Pitching
“A main contributing factor to explain the favorable THM (nacelle + rotor) is the combination of an advanced MultiSmart turbine control system and the application of load reducing cyclic rotor blade pitch technology. The latter continuously monitors blade root loads and adjusts the blade angle accordingly during each rotor revolution,” said Malumbres.
He explained, “as our highest priority was to commence soonest with controller testing and optimizing, we decided to initially fit the prototype with a smaller provisional 107-metre rotor based upon conventional single piece blades.” The segmented rotor blades that are going to be fitted on the prototype consist of glass 
fiber reinforced epoxy composite inner and outer sections joined by a single bolted joint. Malumbres explained that, “Eliminating any risk of a potential stiffness interruption occurring in the joining surface cross section thereby represented a major challenge for our rotor blade designers and required extensive research efforts.”
As far as transportation and erection logistics are concerned, a major advantage, said the company, is that individual blade section lengths are less than 35m. Secondly, similar to the 2-MW erection process again (only) a standard 800- to 1000-tonne crane is required depending on hub height, said Malumbres.
He also explained that “due to the modular concept with easily removable drivetrain and other main components, such a relatively inexpensive crane will be employed to hoist an ‘empty’ nacelle on top of a matching tower.”
FlexiFit Nacelle Mounted Crane
After each job is completed the crane can then move to the next turbine erection location so that a newly developed Gamesa FlexiFit nacelle mounted crane system can take over and hoist in all the main components. The latter crane is a ground assembled self-mounting system capable of either hoisting-in or exchanging-out a complete drive system.
Malumbres is convinced that the FlexiFit solution will be a key contributor towards substantially lowering installation costs and lead to more Gamesa G10X-4.5MW installations in the field.
The company said that it plans to introduce a second prototype next year in close vicinity to the first unit. The next two prototypes — 3 & 4 — are planned for Q2-2011, perhaps 60Hz versions in the U.S., and are to be followed by another twenty pre-series turbines until the end of the year.
The company plans to start series production in 2012 with the U.S., Canada, Spain, Italy, Germany, France and China pinpointed at as likely main markets.
“We have already received lots of interest in the G10x-4.5MW from potential clients in many countries,” said Malumbres confidently.
(Author’s note: G10X-4.5MW Chief Engineer Rafael Hernández and Marketing Manager Juan Diego Díaz also participated in the interview. Some of the quotes below came from them.)
