Tong W. Wind Power Generation and Wind Turbine Design

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Direct Drive Superconducting Wind Generators 325

the wind generators it was desirable to avoid complex liquid cooled systems.

Extensive thermal and CFD modelling showed that the stator could be easily

cooled by forced air ventilation.

6.4.6 Stator iron losses

The stator design contains a laminated iron core located radially behind then airgap

winding. This serves three purposes:

It provides a means of mechanical support and rigidity close to the coil supports. 1.

It shields external components from stray ﬂ ux. 2.

It provides an easy circumferential path for the ﬂ ux passing behind the airgap 3.

winding, reducing the amount of HTS wire required.

It enhances the ﬁ eld in the active region of the stator winding. 4.

A fully airgap design (type 4 above) machine has a signiﬁ cant component of

magnetic ﬂ ux in the axial direction near to and outside of the straight length of the

machine. This can cause eddy currents to ﬂ ow in the radial and tangential direction

in the laminations, causing a high concentration of loss at the ends. The low frequency

of the generator (<2 Hz) was expected to reduce these losses, but the phenomenon was

still seen as a potential risk at the start of the project.

The conceptual design was modelled using Vector Fields Opera 3D electromag-

netic FE software. The original design had a total end loss due to eddy currents of

55 kW, which may have been possible to remove by cooling, but would have had

a detrimental effect on the efﬁ ciency on a machine of only 8 MW rating. Careful

design of the stator core geometry and further modelling resulted in a design with

this loss reduced to 6 kW.

6.5 The cost-beneﬁ t study

In order to justify the business case for the development of the HTS generator,

Converteam Ltd. commissioned the independent wind turbine consultants BVG

Associates Ltd. to analyse the cost/beneﬁ t of very large offshore turbines employ-

ing HTS direct drive generators and medium voltage power converters [40]. This

study involved the design of a complete, notional, 8 MW, 12 rpm rotor wind tur-

bine, with appropriate foundations by Shefﬁ eld Forgemasters, and turbine blade

design, control and structural integration by Garrad Hassan Ltd.

Comparisons were made for a typical UK Crown Estate Round 2 offshore

wind farm of 504 MW containing 4 MW geared conventional DFIG turbines

(the baseline), 8 MW geared turbines, 8 MW direct drive PMG turbines, and 8

MW direct drive HTS turbines. To ensure consistent analysis, the study found

ﬁ rst that on monopile foundations, conventional and PMG 8 MW turbines actu-

ally increased the cost of electricity from the wind farm compared to the base-

line 4 MW turbines. Beneﬁ ts of the Converteam design, low mass, 8 MW HTS

generator resulted in an identical cost of energy compared to the baseline, even

at pre-series volume costs.

326 Wind Power Generation and Wind Turbine Design

Then, retaining the successful 8 MW HTS design, the foundation was replaced

with an alternative more suited to such large turbines in relatively deep water. With

this conﬁ guration, the 8 MW HTS turbines resulted in a 17% reduction in the cost

of energy relative to the baseline, in the same pre-series volumes. The analysis

included the efﬁ ciency beneﬁ ts of HTS generators, but only at part load, since at

wind speeds greater than the minimum required for full load output only part of

the kinetic energy is extracted from the wind and the beneﬁ t of increased generator

efﬁ ciency is limited to reducing the load on the mechanical components. Work is

progressing with a wind turbine manufacturer towards the design and cost analysis

of a new giant turbine, in serial volumes, prior to demonstrator deployment.

6.6 Model generator

Following the completion of the concept design, work started on the design of

the scaled demonstration ‘Model Generator’. Apart from the use of 1G HTS wire

rather than 2G, due to the limited availability and performance of 2G at the time

of the wire purchase, the model generator uses scaled components of the same

type as in the full size generator. The rating of the machine was constrained by the

project budget for HTS wire, and was chosen to be 500 kW at 30 rpm.

At the time of writing (December 2008) the design of the major components has

been completed, and manufacturing was in progress. Manufacturing and testing of

this generator is expected to be completed in 2010.

6.7 Material testing and component prototypes

An important part of the de-risking process for new technology is the manufacture

and test of prototype components.

A test facility was established at the University of Warwick with a cryostat to

enable mechanical and thermal testing of small components at room temperature

and down to a temperature of 30 K. Other tests included material properties for

the support teeth for the airgap stator winding. Figure 17 shows a carbon ﬁ bre

cold-to-warm torque link for the model generator, prior to mechanical testing.

It was also considered essential to manufacture and test smaller versions of the

HTS coils. During the concept design phase, three HTS coils were made to a

design similar to the model generator and full size coils, which were tested in a

Figure 17: Torque link.

Direct Drive Superconducting Wind Generators 327

simulated magnetic circuit in a small cryostat. These coils were successfully tested

up to an operating current of 230 A, compared to the 140 A operating current in the

model generator.

Following on from these tests Converteam opened a cryogenics laboratory in

their Rugby facility to support all HTS projects, with a large cryostat (8 m

vacuum

space) capable of accommodating the coils for the full size wind generator, shown

in Fig. 18 during the setting up of a test.

6.8 The full scale detailed design

Following discussions with a wind turbine manufacturer, the rating of the full size

generator was changed to 10 MW at 11.5 rpm, to suit their planned turbine devel-

opment. The 10 MW design was scaled from the 8 MW concept design, resulting

in a slight increase in diameter to 5.4 m, an increase in length to 2.6 m, and a mass

of less than 140 tonnes.

The design is based on the expected performance of the best HTS wire in 2010,

the earliest time when wire will need to be ordered for the full size prototype gen-

erator. This is expected to require an operating temperature of 40 K. The helium gas

cooling system used in the design permits the operating temperature to be easily

changed when future improvements in HTS wire performance permit.

7 T he way forward

The next logical step will be the manufacture and test of a full size prototype, fol-

lowed by its demonstration on the 10 MW turbine. In parallel with this the supply

chain development and engineering of the manufacturing process for production

manufacturing will take place before the start of commercial volume production,

which could begin by 2015.

Figure 18 : Large cryostat with a prototype HTS coil in a magnetic circuit at

Converteam Ltd., Rugby.

328 Wind Power Generation and Wind Turbine Design

As the performance of the HTS wire improves over the lifetime of the product,

it is expected that the design will evolve. The improvement in wire performance

could be used to increase in the operating temperature of the HTS coils, possibly

to as high as 65 K, thereby considerably reducing the cooling power required.

Alternatively the improvement in performance could be used to reduce the amount

of HTS wire by operating at a higher current, although this change would require

careful mechanical analysis of any resulting increase in forces on the coils.

Further developments are also expected in cryocooler technology. Pulse tube

cooler, with no cold moving parts, are beginning to reach the power levels at the

temperatures required in the HTS wind generator. Pulse tube will offer cooler with

less maintenance and greater reliability, with the potential to locate the entire cryo-

genic cooling system on the rotor, removing the need to transfer cold ﬂ uid through

a rotating seal.

8 Other HTS wind generator projects

In 2007 AMSC announced the start of a $6.8 million project to design a 10 MW

class HTS direct drive wind generator. AMSC are working in partnership with

TECO Westinghouse and with partial funding from NIST. The 30-month project,

like the Converteam project, is also targeting the offshore wind power market. The

project scope is similar to the concept and full size detailed design stages in the

Converteam project.

A design study examining HTS direct drive wind generators at ratings of 2 MW,

21 rpm and 8 MW, 12 rpm was carried out in Japan [ 41 ]. Many conclusions were

similar to those in the Converteam study. The HTS generator designs were reported

as 1/3 to 2/3 of the size on non-superconducting machines, with efﬁ ciency gains

of 1% at full load to 10% at part load. The optimum pole number was found to be

between 16 and 20.

9 Conclusions

The new generation of HTS wire coming to the market is predicted to be available

in volume at a cost low enough to make HTS motors and generators cost competi-

tive with conventional copper and PMGs. The signiﬁ cant size and mass advan-

tages make direct drive HTS generators an enabling technology for the very large

10 MW class turbines that will help reduce the cost of offshore wind energy.

Leading players have substantial developments completed and in demonstra-

tion, and wind power system developers and operators are being invited to appreci-

ate the great potential in superconducting generators.

R eferences

[ 1] Global Wind 2007 Report; Global Wind Energy Council (GWEC), www.

gwec.net

Direct Drive Superconducting Wind Generators 329

[2] Global Wind Energy Outlook 2008; Global Wind Energy Council (GWEC),

www.gwec.net

[3] Clipper Windpower Plc Press Release, The Crown Estate To Purchase The

World's Largest Offshore Wind Turbine From Clipper Windpower For Deploy-

ment In UK Waters, 2008, http://www.clipperwind.com/pr_170408.html

[4] Second Strategic Energy Review. An EU Energy Security and Solidarity

Action Plan; Commission of the European Communities, Brussels 2008.

[5] Giant offshore wind farms to supply half of UK power, Times Online, 2007,

www.timesonline.co.uk/tol/news/environment/article3022277.ece

[6] Datta, R. & Ranganathan, V.T., Variable speed wind power generation using

doubly fed wound rotor induction machine – a comparison with alternative

schemes. IEEE Transactions, Energy Conversion, 17 (3), pp. 414–421, 2002.

[7] Robb, D., The gearbox challenge – the role of bearings in gearbox failures.

Windpower Monthly Magazine , pp. 33–60, 2005.

[8] Capital Grant Scheme for Offshore Wind. Kentish Flats Offshore Wind

Farm. Annual Report January 2006–December 2006, UK Department for

Business Enterprise and Regulatory Reform (BERR), pp. 9–10, www.berr.

gov.uk/ﬁ les/ﬁ le41600.pdf

[9] Ribrant, J. & Bertling, L.M., Survey of failures in wind power systems with

focus on Swedish wind power plants during 1997–2005. IEEE Transaction,

Energy Conversion , 22 (1), 2007.

[10] Musial, W., Butterﬁ eld, S. & McNiff, B., Improving wind turbine gearbox

reliability, Proc. of the 2007 European Wind Energy Conf. , Milan, Italy,

2007.

[11] Wind Turbine Data Summary Tables. WindStats Newsletter , 21 (4), p. 9,

2008

[12] Polinder, H. & van der Pijl, F.A., Comparison of direct drive and geared

concepts for wind turbines, IEEE Transactions, Energy Conversion , 21 (3),

pp. 725–733, 2006.

[13] Lewis, C., The advanced induction motor. Power Engineering Society Sum-

mer Meeting, 2002 IEEE , pp. 250–253, 2002.

[14] Onnes, H.K., The resistance of pure mercury at helium temperature. Leiden

Commun ., 120b , 1911.

[15] Meissner, W.,R., Ein neuer Effekt bei Eintritt der Supraleitfähigkeit. Natur-

wissenschaften , 21 (44), pp. 787–788, 1933.

[16] Elkin, J.W., Superconductors (Chapter 13). Materials at Low Temperatures ,

ed. R.P. Reed & A.F. Clark, American Society for Metals: Ohio, 1983.

[17] Wilson, M.N., Superconducting magnets (Chapter 12). Superconducting

Materials and Their Manufacture , Oxford University Press: Oxford, 1983.

[18] Bednorz, J.G. & Müller, K.A., Possible high T

superconductivity in the

Ba − La − Cu − O system. Zeitschrift für Physik B: Condensed Matter , 64 (1),

pp. 189–193, 1986.

[19] Kalsi, S., Weeber, K., Takesue, H., Lewis, C., Neumueller, H.-W. & Blaugher,

R.D., Development status of rotating machines employing superconducting

ﬁ eld windings. IEEE Proceedings , 92 (10), pp. 1688–1704, 2004.

330 Wind Power Generation and Wind Turbine Design

[20] Hull, J.R. & Murakami, M., Applications of bulk high temperature super-

conductors, IEEE Proceedings , 92 (10), pp. 1705–1718, 2004.

[21] Masson, P.J. & Luongo, C.A., High power density superconducting motor

for all-electric aircraft propulsion. IEEE Transactions, Applied Supercon-

ductivity , 15 (2), pp. 2226–2229, 2005.

[22] Superczynski, M.J. & Waltman, D.J., Homopolar motor with high tempera-

ture superconductor ﬁ eld windings. IEEE Transactions, Applied Supercon-

ductivity , 7 (2), pp. 513–518, 1997.

[23] Nakamura, T., Miyake, H., Ogama, Y., Morita, G., Muta, I. & Hoshino, T.,

Fabrication and characteristics of HTS induction motor by the use of B1-

2223/Ag squirrel-cage rotor. IEEE Transactions, Applied Superconductiv-

ity , 16 (2), pp. 1469–1472, 2006 .

[ 24] Buck, J., Hartman, B., Ricket, R., Gamble, B., MacDonald, T. & Snitchler,

G., Factor testing of a 36.5 MW high temperature superconducting propul-

sion motor. Proc. of the American Society of Naval Engineers (ASNE) Sym-

posium , 2007.

[25] Snitchler, G., Gamble, B. & Kalsi, S., The performance of a 5 MW high

temperature superconducting superconductor ship propulsion motor. IEEE

Transactions, Applied Superconductivity , 15 (2), pp. 2206–2209, 2005.

[26] Steurer, M., Woodruff, S., Boenig, H., Bogdan, F. & Sloderbeck, M.,

Hardware-in-the-loop experiments with a 5 MW HTS propulsion motor at

Florida State University’s power test facility. Proc. of IEEE Power Engineering

Society General Meeting , pp. 1–4, 2007.

[27] Malozemoff, A.P., Maguire, J., Gamble, B. & Kalsi, S., Power applications

of high temperature superconductors: status and perspectives. IEEE Trans-

actions Applied Superconductivity , 12 (1), pp. 778–781, 1992.

[28] Stone, G.C., Advancements during the past quarter century in on-line moni-

toring of motor and generator winding insulation. IEEE Transactions on Di-

electrics and Electrical Insulation , 9 (5), pp. 746–751, 2002.

[29] Kalsi, S., Superconducting generators promise higher reliability and ease

of operation. Presented at American Society of Naval Engineers, Electrical

Machines Technology Symposium , Philadelphia, PA, 2004.

[30] Dietrich, M., Yang, L.W. & Thummes, G., High power stirling-type pulse

tube cryocooler: observation and reduction of regenerator temperature

inhomogeneties. Cryogenics , 47 (5-6), pp. 306–314, 2007.

[31] Vitale, N.G., Striling free piston cryocoolers, US Patent 5,022,229, 1991.

[32] Malozemoff, A.P., Fleshler, S., Rupich, M., Thieme, C., Li, X., Zhang,

W., Otto, A., Maguire, J., Folts, D., Yuan, J., Kraemer, H.-P., Schmidt, W.,

Wohlfart, M. & Neumueller, H.-W., Progress in HTS coated conductors and

their applications. Superconductor Science and Technology , 21 034005 (7

pp.), doi: 10.1088/0953-2048/21/3/034005, 2008.

[33] Selvamanickam, V., Chen, Y., Xiong, X., Xie, Y.Y., Reeves, J.L., Zhang, X.,

Qiao, Y., Lenseth, K.P., Schmidt, R.M., Rar, A., Hazelton, D.W. & Teklet-

sadik, K., Recent progress in second-generation HTS conductor scale-up at

superpower. IEEE Transactions, Applied Superconductivity , 17 (2), 2007.

Direct Drive Superconducting Wind Generators 331

[34] Lewis, C. & Muller, J., A direct drive wind turbine HTS generator.

Power Engineering Society General Meeting , IEEE, 24–28 June 2007,

http:// ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=4275835&

isnumber=4275199

[35] Senju, T., Sakamoto, R., Funabashi, T., Fujita, H. & Sekine, H., Output

power levelling of wind turbine generator for all operating regions by pitch

angle control . IEEE Transactions Energy Conversion , 21 (2), 2006.

[36] Tsukamoto, O., Alamgir, A.K.M., Liu, M., Miyagi, D. & Ohmatsu, K., AC

loss characteristics of stacked conductors with magnetic substrates. IEEE

Transactions Applied Superconductivity , 17 (2), 2007.

[37] Fee, M., Staines, M.P., Buckley, R.G., Watterson, P.A. & Zhu, J.G., Calcu-

lation of AC loss in an HTS Wind Turbine Generator. IEEE Transactions

Applied Superconductivity , 13 (2), 2003.

[38] Eckels, P.W. & Snitchler, G., 5 MW high temperature superconducting pro-

pulsion motor design and test results. Naval Engineers Journal , 117 (4), pp.

31–36, 2005.

[39] Frank, M., Frauenhofer, J., Gromoll, B., Hasselt, P., Nick W., Nerowski, G.,

Neumueller, H.-W., Haefner, H.-U. & Thummes, G., Thermosyphon cool-

ing system for the Siemens 400 kW HTS synchronous machines. AIP Conf.

Proc. , 710 (1), pp. 859–866, 2004.

[40] Valpy, B., Establishing the cost of energy beneﬁ ts of the HTS generator

technology, Report by BVG Associates for Converteam.

[41] Maki, N., Design study of high temperature superconducting generators for

wind power systems. Journal of Physics Conference Series 97, doi:10.1088/

1742-6596/97/1/012155, 2008.

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CHAPTER 10

Intelligent wind power unit with tandem

wind rotors

Toshiaki Kanemoto

& Koichi Kubo

Faculty of Engineering, Kyushu Institute of Technology, Japan.

Graduate School of Engineering, Kyushu Institute of Technology, Japan.

Wind is clean, renewable and home grown energy source of the electric power gen-

eration, and has been positively/effectively utilized to cope with the warming global

environment. The propeller type wind turbines play main role in the wind power gen-

eration; however, it may have some weak points. To overcome the weak points of the

traditional one, the authors have investigated the superior wind turbine unit which is

composed of the tandem wind rotors and the double rotational armature type generator

without the traditional stator. The large-sized front wind rotor and the small-sized rear

wind rotor drive the inner and the outer rotational armatures respectively, in keeping

the rotational torque counter-balanced. Such operating conditions may be able to make

the output higher than the traditional wind turbines, and to keep the output constant

in the rated operation mode without the brakes and/or pitch control mechanism. The

ﬁ rst step toward practical use of this wind power unit, the characteristics of the double

rotational armature type synchronous generator and the double rotational armature

type doubly fed induction generator were investigated. Moreover, the desirable proﬁ les

of tandem wind rotors such as optimum diameter ratio (rear rotor diameter divided by

front rotor diameter), blade numbers of both wind rotors and axial distance between

both wind rotors were also investigated. Furthermore, the ﬁ eld tests of the wind turbine

unit had been carried out on the pick-up type truck driven straight at constant speed.

1 Introduction

The propeller type wind turbines play main role in the electric power generation.

The traditional propeller types may, however, have some weak points as follows:

The large-sized wind rotor generates the fruitful output but is not operated at 1.

the weak wind, while the small-sized wind rotor can be operated at the weak

wind but the output is small.

334 Wind Power Generation and Wind Turbine Design

It is necessary to equip the wind rotor with the brakes and/or the pitch control 2.

mechanisms, to suppress the abnormal rotation and the overload at the strong

wind. To keep good quality of the electric power by increasing the rotational

speed of the armature, it is necessary to prepare the large-sized generator with

multi-poles or the accelerating gearbox.

There are few areas applicable to the traditional wind turbine with the rated 3.

mode at the wind velocity faster than 11 m/s. It is desired, for the next leap of

the wind turbine technologies, to get the fruitful output at not only rich but also

poor wind circumstances.

To overcome above weak points, the authors invented the superior wind power

unit called “intelligent wind power unit”. This unit is composed of the large-sized

front wind rotor, the small-sized rear wind rotor and the peculiar generator with the

inner and the outer rotational armatures without the traditional stator. The front and

the rear wind rotors drive the inner and the outer armatures in the upwind type or

drive the outer and the inner armatures in the downwind type, respectively. The rota-

tional direction and speed of both wind rotors/armatures are free, and automatically

and smartly adjusted pretty well in response to the wind circumstances. This unit is

applicable to the area with not only rich wind circumstances such as Middlegrunden

offshore [ 1 ], but also poor circumstances having weak and/or ﬂ uctuating wind.

2 Previous works on tandem wind rotors

The idea of the tandem wind rotors has been proposed [ 2 ], and Ushiyama et al.

could also increase the output using the model tandem wind rotors, as follows [ 3 ].

The front wind rotor consists of six blades with the diameter of 0.8 m, and the rear

wind rotor consists of three blades with the diameter of 1.2 m, as shown in Fig. 1 .

The front and the rear wind rotors are connected directly to the stator casing and

the armature of the traditional generator, respectively. The outputs against the rela-

tive rotational speed are shown in Fig. 2 . The maximum outputs are 2.6 W at the

wind velocity V = 6 m/s, 19.8 W at V = 8 m/s, and 38.9 W at V = 10 m/s, in the

experimental results. This paper discusses the output in the followings. The rated

output of the generator is 36 W at the rotational speed N

= 950 min

− 1

but the

actual output is 38.9 W with N

= 768 min

− 1

at 10 m/s. That is, the output is higher

than the rated output even if the rotational speed is slower than the rated speed,

and the relative rotational speed is increased by the counter-rotation. As a result,

this paper concluded that the experimental results of the model demonstrated the

technical possibility of the counter-rotating-type wind turbine generator. Jang and

Heo brought recently the above ideas into his researches and has proposed the

tandem type composed of the small-sized front wind rotor and the large-sized rear

wind rotor [ 4 ].

In 2002, Appa Technology Initiative developed the counter-rotating type wind

turbine (CRWT) and the prototype was supplied to the ﬁ eld tests in California. The

prototype composed of tandem wind rotors, whose diameters are 4 m and blade

numbers are 2 with the tip speed ratio l = 6, and the isolated traditional generator