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In its nascent stages today, the offshore wind power market is expected to enter a periodof rapid and prolonged growth beginning within the next several years. The developmentof higher capacity wind energy systems will be required to fully capitalize on this vastclean energy resource.

MARTIN FISCHER, VICE PRESIDENT OF AMERICAN SUPERCONDUCTOR, GENERAL MANAGER OF AMSC AUSTRIA AND SUDHIR GADH,COUNTRY MANAGER, INDIA, AMERICAN SUPERCONDUCTOR

High Temperature Superconductors Enable the

World’s Largest and Most Powerful Wind Turbine

Reecting the scope of the growthexpected for this market, industryresearch rm IHS Emerging Energy

Research, currently projects that globaloffshore installed capacity will increase toapproximately 20 GW by 2015 and risesharply to 104 GW by 2025.

Until now, among the greatest chal-lenges to developing larger wind turbinesfor both onshore and offshore use havebeen the practical size and weight limita-tions of the wind turbine generator. The

power density advantage of superconduc-tors, however, is now being applied to windturbine generators to maximize the ‘powerper tower’ of multi-megawatt turbines,while at the same time overcoming sizeand weight barriers – and reducing over-all project costs. Utilizing superconductordirect drive generators, SeaTitan™ windturbines are being designed to produce 10megawatts (MW) or more of power whichwould make them the world’s largest andmost powerful wind turbines.

Superconductor Turbines for theOffshore EnvironmentAmerican Superconductor (AMSC) is de-veloping the SeaTitan wind energy sys-tem by combining the company’s world-renowned wind turbine engineeringexperience with its leadership in the su-perconductor arena. The superconductorgenerators to be used in SeaTitan windturbines are based largely on proven su-perconductor ship propulsion motors and

generator technology developed by AMSCfor the United States Navy. The uniquepower density of superconductors will en-able a 10 MW SeaTitan wind turbine to besimilar in weight and size to a conventional

5 MW system. This breakthrough windturbine will signicantly lower offshorewind development and maintenance costsand create a path forward to wind genera-tor power ratings of 10 MW and beyond.

Offshore wind energy has many ad-vantages compared to onshore, includinghigher wind speeds with less intermittencyand greater availability of space. In ad-dition to offering aesthetic advantages,offshore sites also are typically located incloser proximity to high power demand

population centers.While the size of the world’s offshore

resource is huge, the costs of capitalizingon this market currently are about 50 per-cent higher compared to onshore wind de-velopment on a rst-cost basis. Part of thisadded cost premium is due to less than op-timal “adaptation” of conventional tech-nology with ad hoc design modicationssuch as sealed nacelles and special accessplatforms for maintenance purposes. Be-cause the majority of costs associated

with offshore wind are related to instal-lation and the subsea support structures,the most effective way to reduce costs isby maximizing the amount of ‘power pertower’ produced by each turbine such asachieved by utilizing superconductor gen-erators.

Power Density of Superconductorsto Enable Power Ratings of 10 MWand BeyondWind turbines being employed today for

the offshore market are currently limitedto power ratings of approximately 5 - 6MW in capacity, partly due to the factthe drive trains for these conventionalmulti-MW turbines are very heavy and

have unresolved reliability issues. Allow-ance for tolerances and deformations inlarge generators reduce the effectivenessof Permanent Magnet (PM) generators.What is needed to fully capitalize on theopportunity presented by offshore windis the design of special purpose machineswith inherent high efciency and lowermaintenance requirements. The generatordeveloped by AMSC achieves this by utiliz-ing the company’s Amperium™ high tem-perature superconductor (HTS) wire, which

is capable of conducting more than 100times the electrical current (“amperage”)of copper wire of the same dimensions.The resulting power density of these sys-tems compared to conventional genera-tors using copper wire will break this exist-ing power rating barrier and enable thesesmaller-sized turbines that are capable ofproducing more power per tower.

By eliminating copper in the turbinerotor and instead using superconductor ro-tors, the wind generator is not only much

smaller and lighter, but more efcient andless expensive than conventional large-scale wind turbine generators. Efciencyis further enhanced – and manufacturingand maintenance costs reduced in theSeaTitan wind turbine design – by usinga direct drive generator, thus eliminatingthe complex turbine gearbox, which tendsto be the most maintenance intensivewind turbine component. Superconduc-tor technology has already been provennumerous times in many applications,

including large-scale power cables androtating machine platforms such as largeship propulsion motors. In fact, a 36.5MW superconductor ship propulsion mo-tor designed and manufactured by AMSC

WIND POWER

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for the U.S. Navy successfully completed

the Navy’s full-load power testing in Janu-ary 2009. These machines are now readyfor deployment.

The weight savings attributable to HTStechnology allows the SeaTitan wind tur-bine generator to be placed directly abovethe tower. This enables improved main-frame design and direct load transfer fromthe hub to the tower offering. In mostexisting offshore wind turbines, a majorfailure mode is caused by the deectionsof the rotor shaft. To reduce damage, the

housing of the gearboxes or generatorscould be decoupled from the mainframe,but only in a complex way. This is notneeded for the superconductor generatorsbecause their large airgap can absorb alldeections, allowing the generator hous-ing to be directly integrated in the windturbine mainframe. This factor, combinedwith the signi cantly small generator di-ameter, is the primary contributor to thestrength, light weight and small size of theSeaTitan wind turbine design. Further, the

SeaTitan wind turbine requires only onemain bearing conguration.

New Technology Paradigm on theHorizonThe SeaTitan wind turbine additionallyincorporates a number of design solu-tions that ensure redundancy of its opera-tion. For example, the cryogenic coolingsystem for the HTS generator achieveshigh reliability by employing n+1 modu-lar, single-stage Gifford McMahon (GM)

coolers and long-life seals in its heliumtransfer coupling. In fact, in AMSC’s ex-perience with cooling transfer systems inboth HTS transmission and large rotatingmachines, the reliability of this component

has proven to be excellent. The SeaTitan

wind turbine design, which is equippedwith more than one cryogenically cooledsurface, also promotes efciency and eas-es maintenance. Having more than onecryogenically cooled surface in series al-lows each of these surfaces to work lessto lower the temperature of the cryogenicuid. Also, if one cryogenically cooled sur-face malfunctions, the redundancy in thesystem will be able to overcome the loss.The refrigeration system additionally hasno unusual environmental requirement

or impact due to the required cryogeniccooling components for an HTS genera-tor. In fact, most serviceable componentsare placed at the bottom of the tower foreasy access. These accessible componentsinclude power converters, compressors forcryogenic cooling, the control cabinet, andswitchgear.

Superconductor Turbines EnteringPrototype StageIn addition to the SeaTitan wind turbine,

as part of its Windtec™ product line,AMSC provides a variety of licenses andcustomized designs for onshore and off-shore turbines. More than a dozen windturbine manufacturers today are utilizingthe company’s suite of conventional windturbines with power ratings up to 6 MW.The company also provides extensive cus-tomer support services through manufac-turing scale up as well as advanced electri-cal control systems for each wind turbinethat its customers produce.

The SeaTitan wind turbine will havean initial design capacity of 10 MW with a190-meter rotor. AMSC recently acquireda 25 percent stake in UK-based Blade Dy-namics Ltd. which has developed wind

turbine blade technologies designed to

increase the efciency and performance ofmulti-megawatt wind turbines while alsoreducing costs. In addition to providingAMSC wind turbine design licensees witha differentiated blade offering, Blade Dy-namics’ unique technology will also pro-vide a compelling blade platform for theSeaTitan wind turbine. The tower can reston conventional jacket foundations anddeep water foundations of various types.

AMSC expects to select its rst SeaTi-tan wind turbine licensee in the months

ahead. It will then work with this custom-er to establish a full supply chain for thiswind turbine, including a manufacturer forthe SeaTitan generator. AMSC expectsthat its licensees will enter full-volume pro-duction by mid-decade.

The Global RaceWhile Europe has traditionally been theleader in the offshore wind market, therest of the world is moving aggressivelyto catch-up. Currently, India’s wind power

plants are limited to onshore today, butthe country, with its 7,000 km of coastline,has incredible offshore potential.

Offshore wind power expected toenter a period of rapid and prolongedgrowth. Right now, the global race is any-one’s to win. The nation that can seize aleadership role will not only create and in-dustry and thousands of jobs for years tocome but will also boast a lowered cost ofenergy, cleaner power and a path towardsenergy independence.

If India moves forward with offshorewith the same momentum that it ap-proached the onshore wind industry, itcould be a major contender in the offshorerace.