Study of 10 MW SG

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IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 21, NO. 3, JUNE 2011 1151

Study of 10 MW-Class Wind Turbine SynchronousGenerators With HTS Field Windings

Satoshi Fukui, Jun Ogawa, Takao Sato, Osami Tsukamoto, Naoji Kashima, and Shigeo Nagaya

Abstract—We study the electro-magnetic design of 10 MW-classwind turbine generator with high temperature superconductingfield winding by using the FEM analysis. The design examples arepresented and the generator characteristics are investigated. The10 MW-class HTS wind turbine generator is considered to be fea-sible from the stand point of the electro-magnetic design. In thisstudy, 8-pole and 12-pole generators are investigated. From the re-sults, it is considered that the 8-pole design is preferable comparedwith the 12-pole design. The analysis also reveals the small syn-chronous reactance of the HTS wind turbine generator. Therefore,proper protection is necessary for the large short circuit current.

Index Terms—HTS field winding, synchronous generator, wind

turbine generator.

I. INTRODUCTION

DEVELOPMENT and introduction of wind power gener-ators have recently advanced in the R & D of renewable

energies [1]–[3]. Scaling-up of wind turbines is one of recent R& D trends because of the scale merits. In the present situation,it is considered that a 5 MW wind turbine is the power limit of the conventional generator technology. However, a further in-crease of the out-put power of the wind turbine generators, morethan 5 MW, is required. Therefore, a break-thought technology

to develop light weight and compact wind turbine generators issurely expected [4]–[6].

With recent progress of fabrication technologies of longlength and high critical current 2G HTS tapes (ex. YBCOtape), it is promising to develop high magnetic field HTS coilsfor power apparatuses. By applying HTS to the wind turbinegenerators, it is expected to provide the light weight and com-pact design, since the magnetic field can be higher comparedwith the conventional generator, so that the iron core can beconsiderably reduced. Therefore, it is considered that the appli-cation of the HTS technology to the wind turbine generator isone of the key issues to break the technical power limit of theconventional wind turbine generator. In this study, we focus to

apply high temperature superconductivity for the 10 MW-class

Manuscript received August 03, 2010; accepted October 21, 2010. Date of publication November 18, 2010; date of current version May 27, 2011. Thiswork supported in part by Chubu Electric Power Co. Inc.

S. Fukui, J. Ogawa, and T. Sato are with Graduate School of Science andTechnology, Niigata University, Niigata, 950-2181, Japan (e-mail: [email protected]).

O. Tsukamoto is with Yokohama National University, Kanagawa, 240-8501,Japan (e-mail: [email protected]).

N. Kashima and S. Nagaya are with Chubu Electric Power Co. Inc., Aichi,459-8522, Japan (e-mail: [email protected]).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TASC.2010.2090115

TABLE IBASIC DESIGN CONDITION OF 10 MW WIND TURBINE GENERATOR

wind turbine generators. In this paper, the electromagneticdesign of 10 MW-class wind turbine synchronous generatorwith HTS field windings is studied. The design examples of theHTS wind turbine generator are presented and the generatorcharacteristics are discussed.

II. ELECTRO-MAGNETIC DESIGN OF 10 MW HTS WIND

TURBINE GENERATOR

A. Design Condition

The electro-magnetic design of 10 MW wind turbine gener-

ator with HTS field windings is performed by using FEM anal-ysis. In this study, the 3-phase generator with the rated voltageof 3.3 kV (phase-to-phase) is considered. The number of therevolution is 10 rpm [5]. In Table I, the basic design conditionis summarized.

B. High Temperature Superconducting Field Winding

For the HTS field winding, the high magnetic field design isnecessary to effectively use the advantage of HTS. In this de-sign, we consider that the strength of the main magnetic fieldproduced by the HTS field windings at the position of the ar-mature winding should be 2.5–3 T which exceeds the saturation

value of the magnetic field in the conventional magnetic corematerial. To secure the highermagnetic field, the armature wind-ings should be supported in the non-magnetic material and theback yoke made of the magnetic material is used for the purposeof magnetic shield. In this analysis, it is considered that the HTSfield winding is operated at 20 K and the rated current density

is set at . Fig. 1 shows the schematic il-lustrations of the cross section and the FEM models of the windturbine generators with the HTS field windings which are anal-ysed in this study. The sizes of the HTS field coil are also shownin Fig. 1. As shown in Fig. 1, the model-1 is for the case of 8-polegenerator and the model-2 is for the case of 12-pole generatorrespectively. The FEM analysis is firstly performed to obtain the

magnetic field distribution around the armature winding. Fig. 2

1051-8223/$26.00 © 2010 IEEE



1152 IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 21, NO. 3, JUNE 2011

Fig. 1. Schematic illustrations of cross section of 10 MW HTS wind turbinegenerators and their FEM models. (a) Model-1 (8-pole) and (b) model-2 (12-pole).

shows the distributions of the radial magnetic field on the az-imuthal l ine o f , 1 446 m m and 1 456 m m. I t is con-firmed that the magnetic field around the armature winding canbe around 2.5–3 T. From the data shown in Fig. 2, the magneticfield in the model-2 is smaller than that in the model-1. When thepole number becomes large with same diameter, the distance be-tween the neighboring field coils decreases. The magnetic fluxproduced by the field coils passes nearby the field coils and themagnetic field around the armature windings decreases. It isalso found that the necessary amount of the HTS wire for themodel-1 is much smaller than that for the model-2. Therefore,

it is considered that the 8-pole design (model-1) is preferablecompared with the 12-pole design (model-2). As also shownin Fig. 2(a), the magnetic field at is saturated.This is the effect of the magnetic saturation of the back yoke. InTable II, the specifications of the HTS field winding are sum-marized.

C. Armature Winding

In this design, we consider that the armature winding is the2-layer winding with the distributed structure. The slot num-bers per phase and per pole are for the model-1 and

for the model-2 respectively. For the FEM analysis, thenumber of the Cu armature conductor in each slot, , must be

estimated. Assuming that spatial distribution of the magneticfield is sinusoidal with the amplitude of , the induced phase

Fig. 2. Distribution of radial components of magnetic field around armaturewinding. (a) Model-1 (8-pole) and (b) model-2 (12-pole).

voltage (phase-to-ground) in the armature winding, , is ap-proximately expressed by

(1)

where is the rated revolution (rpm), is the mean radiusof the armature winding, is the length along the generatoraxis which is effective for the power conversion, is the polenumber. should be an even number becasuse of the 2-layerwinding. Considering the data shown in Fig. 2, isused. The cross section of the slot and Cu conductor for the ar-mature winding should also be determined by considering thegeometrical constraints as follows.

(2)

(3)

(4)

(5)

where and are the cross section and the current densityofthe Cuarea inthe armatureconductor respectively, isthepacking factor of the Cu in the slot, and are the slotheight and the slot width respectively, and are the heightand the width of the Cu part in the armature conductor respec-tively. Based on the above consideration, the specifications of the armature windings are determined as shown in Table II.

III. FEM ANALYSIS OF GENERATOR MODELS

A. Basic Characteristics

The basic generator characteristics of the model-1 and themodel-2 are investigated based on the results of the FEM



FUKUI et al.: 10 MW-CLASS WIND TURBINE SYNCHRONOUS GENERATORS WITH HTS FIELD WINDINGS 1153

TABLE IIDESIGN SPECIFICATIONS OF 10 MW WIND TURBINE GENERATOR

analysis. Figs. 3(a) and 3(c) show the waveforms of the phasevoltage at the rated field current and the rated revolution. Theroot mean square values of the phase voltage obtained by theFFT of the voltage waveforms are plotted against the frequencyin Figs. 3(b) and 3(d). From the data shown in Fig. 3, it isconfirmed that the phase voltage can be secured for the outputpower of 10 MW. It is also shown in Fig. 3 that there are nosignificant high harmonic components in the phase voltage.The no-load saturation curves and the short-circuit curves are

obtained from the FEM analysis and the data are shown inFig. 4. In Fig. 4, the horizontal axis represents the ratio of thecurrent density of the field winding to that of the rated value,

. As shown in Fig. 4, the short-circuit curves are verysharp against the normalized field current, since the magneticinduction of the armature winding is much smaller than thatof the HTS field winding. Therefore, we consider that thecalculation of the synchronous reactance from the data in Fig. 4is difficult. The synchronous reactance should be determinedfrom the data of the resistance-load analysis shown in the nestsection.

B. Resistance-Load Analysis

The resistance-load analysis is performed combining theFEM analysis and the circuit analysis. In this analysis, the

Fig. 3. Phase voltage waveforms and root mean square values of phase voltagein no-load analysis. (a) and (b) model-1, (c) and (d) model-2.

balanced 3-phase resistive load is connected to the generatormodel. In this analysis, the values of the resistance are 1.03

for the model-1 and 0.99 for the model-2 respectively,which are determined for the output power of 10 MW. Fig. 5shows the waveforms of the phase voltage and the line currentobtained by the resistance-load analysis. From the voltageand current waveforms shown in Fig. 5, it is confirmed thatoutput power is 10.1 MW for the model-1 and 9.83 MW forthe model-2 respectively. The synchronous reactance is alsoobtained from the consideration of the equivalent circuit of synchronous generator and using the data shown in Fig. 5. Thevalues of the synchronous reactance are 0.203 (0.198 pu) for

the model-1 and 0.217 (0.215 pu) for the model-2. This smallvalue of the synchronous reactance is the unique feature of the



1154 IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 21, NO. 3, JUNE 2011

Fig. 4. No-load saturation curves and short-circuit curves. (a) Model-1 and (b)model-2.

superconducting machine, since the magnetic induction of thearmature winding is much smaller than that of the HTS fieldwinding. A similar result is reported in [6]. Generally, the small

synchronous reactance may cause the large short circuit currentin the case of accidents. It is considered that proper protectionmethods should be combined in the case of actual installation.

IV. SUMMARY

The electro-magnetic design of the 10 MW-class wind tur-bine generator with the HTS field winding was studied in thispaper. Two possible design examples were presented and thegenerator characteristics were investigated by using the FEManalysis. It is considered that the 10 MW-class HTS wind tur-bine generator is feasible from the stand point of the electro-magnetic design. It was found from the FEM analysis that the

magnetic field in the 12-pole design is smaller than that in the8-pole design. The necessary length of the HTS wire for the8-pole design was significantly smaller than that for the 12-poledesign. The total amount of the Cu in armature winding of the8-pole design was also smaller than that of the 12-pole design.Therefore, it is concluded that the 8-pole design is preferablecompared with the 12-pole design. It was notable that signifi-cant high harmonic components in the voltage and current werenot observed. This is effective from the view point of the AC

Fig. 5. Waveforms of phase voltage and line current in case of resistance-loadanalysis. (a) Model-1 and (b) model-2.

loss reduction. It was also pointed out that the synchronous re-sistance was very small. If the synchronous reactance of the gen-erator is small, the short circuit current in the case of the accidentbecomes large. Therefore, proper protections should be studied

together with the development of the HTS wind generator.

ACKNOWLEDGMENT

Theauthors would like to thank Prof. H. Ohsaki of the Univer-sity of Tokyo for the useful discussions and Mr. M. Hasegawaof Niigata University for the assistance of FEM analysis.

REFERENCES

[1] US DOE EERE , 2008 [Online]. Available: http://www.eere.en-ergy.gov/DOE/GO-102008-2567

[2] Enercon Wind Turbines [Online]. Available: http://www.enercon.de/ [3] G. M. J. Herbert, S. Iniyan, E. Sreevalsan, and S. Rajapandian, “A re-

viewof wind energy technologies,” Renewable and Sustainable Energy Reviews, vol. 11, pp. 1117–1145, 2007.[4] C. Lewis and J. Muller, “A direct drive wind turbine HTS generator,”

in IEEE Power Engineering Society General Meeting, 2007, pp. 1–8.[5] A. B. Abrahamsen, N. Nijatovic, E. Seiler, T. Zirngihl, C. Træholt, F.

B. Nørgard, N. F. Pedersen, N. H. Andersen, and J. Østergard, “Su-perconducting wind turbine generators,” Superconductor Science and

Technology, vol. 23, p. 034019, 2010.[6] G. Snitchler,“Progress on high temperature superconductor propulsion

motors and direct drive wind generators,” presentedat the The 2011 In-ternational Power Electronics Conference, Sapporo, Japan, 2011 [On-line]. Available: http://www.ipec2010.org/

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