desarrollo de superconductores para motores de propulsion

7/28/2019 Desarrollo de Superconductores Para Motores de Propulsion

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1. Introduction

The Kyoto Protocol adopted at COP3, whichrequires developed nations to reduce their greenhousegas emissions, has brought about large-scale efforts toreduce carbon dioxide emissions in all industry sectors.The transportation sector, including such means asautomobiles, trains and coastal-shipping vessels, isresponsible for around twenty percent of all carbondioxide emissions in Japan, and the amount of emis-sions is increasing year by year. In the automobile indus-try, development of environmental cars like fuel-cell

vehicles is moving ahead at a fast pitch. In coastal ship-ping, the use of high-temperature superconductingmotor in pod-propulsion systems is lately attracting con-siderable attentions.

A pod-propulsion system is usually suspended belowthe bottom of the ships stern and it consists of a motorinstalled inside a pod-shaped container and a generator.One of the advantages of this system is that it has asmaller propulsion resistance than the standard propul-sion systems that are currently in use. However, theproblem with the pod-propulsion system is that the resis-tance to propulsion does not become small when a nor-mal-conducting motor using standard copper coils isused. Thus, an industry-university collaborative research

group was formed to carry out the development of ahigh-temperature superconducting motor (HTS motor)for pod-propulsion systems that can achieve a largermotor output than a copper motor of the same size.

The members of the collaborative research groupare listed in Table 1. Sumitomo Electric Industries, Ltd.is engaged in the development of the high-temperaturesuperconducting coil (HTS coil). In 2005 the collabora-tive research group developed a high-temperaturesuperconducting pod-propulsion system (HTS pod-propulsion system) that provided an output of 12.5 kWand successfully demonstrated that the HTS pod-propul-sion system is highly effective (1). As the first step in

developing a MW-class HTS pod-propulsion system,since 2006 the collaborative research group is carrying

out the development of the permanent-magnet high-temperature superconducting motor (PM-HTS motor)that has an output of 400 kW and is applicable tocoastal-shipping vessels like cement carriers and ferries.In this paper Sumitomo Electrics development of HTScoils is described and the load test results of the 400-kWPM-HTS motor (2) developed by the collaborativeresearch group are reported.

2. Outline of PM-HTS motor

The schematic diagram of a PM-HTS motor isshown in Fig. 1. The developed 400-kW PM-HTS motoris an axial-gap motor and it consists of the magneticfield systems made of permanent magnets and an arma-ture with HTS coils. The HTS coils are cooled to around68 K by a cyclic refrigeration system using liquid nitro-gen. The HTS coil armature is put between the twomagnetic field systems that consist of permanent mag-

nets. The rotary axes are attached to the two magneticfield systems and not to the HTS coils. Because the HTS

SEI TECHNICAL REVIEW NUMBER 65 OCTOBER 2007 41

ELECTRIC WIRE & CABLE, ENERGY

The development of a high-temperature superconducting motor for pod-propulsion system for marine

application is currently conducted by an industry-university collaborative research group. The group has

developed an axial gap-type motor that consists of superconducting armature coils and permanent magnets.

This motor was designed to give an output of 400 kW. As a member of the collaborative research group,

Sumitomo Electric Industries developed the superconducting armature coil based on the results of the

analyses of magnetic field, electromagnetic force and heat. Various tests including the locked rotor test were

performed on the motor and it was proven that the motor has a 400 -kW output.

Development of Superconducting Coil for Ship Pod-Propulsion Motors

Koso FUJINO, Toshihiro HAYASHI, Takeshi SANAMI, Koji HISADA, Kazuya OHMATSU

and Toru OKAZAKI

Table 1. Industry-university collaborative research group

Hitachi, Ltd. Electric power system design

Organization(alphabetical order)

Role

IHI Corporation Project management

Fuji Electric Systems Co., Ltd.Electric power system designand supply

Nakashima Propeller Co., Ltd. Propeller design and supply

Niigata Power Systems Co., Ltd.Pod propulsion mechanicaldesign and supply

Sumitomo Electric Industries,Ltd.

High-temperature supercon-ducting coil design and supply

Taiyo Nippon Sanso CorporationCooling system design and sup-ply

University of Fukui(Professor H. Sugimoto)

Electric and magnetic circuitdesign


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coils are secured, the PM-HTS motor does not requirerotary joints for circulating the coolant.

The critical current (Ic) of a high-temperaturesuperconducting wire becomes higher as the coolanttemperature becomes lower. The HTS motors devel-oped up to this day by institutions around the world

were generally cooled by coolants that have lower tem-perature than liquid nitrogen, such as liquid heliumand liquid neon. However, these coolants are veryexpensive and their latent heats are small in contrast

with that of liquid nitrogen, so the cost for coolingbecomes high. Using liquid nitrogen as a coolant leadsto a much lower HTS motor cost, but Ic of a supercon-ducting wire in liquid nitrogen is much lower in con-trast with that in liquid helium or liquid neon. Lower Icmeans that the magnetic flux in a coil declines andtherefore results in the degradation of the output of anHTS motor. To resolve this problem of liquid nitrogen,the authors contrived to have an iron core called fluxcollector put into each HTS coil so that the magneticflux is enhanced. This has allowed the HTS motor togenerate an output of a practical level.

3. Development of HTS motor

3-1 Design of HTS motor

An HTS coil armature consists of six coils, which aretwo U-phase coils, two V-phase coils and two W-phasecoils. Each coil is made by winding a superconducting

wire. The superconducting wire used is SumitomoElectrics DI-BSCCO (Dynamically-Innovative BSCCO)

wire manufactured using the Companys original CT-OP(Controlled Over Pressure) sintering process. DI-BSCCO has higher Ic than the conventional supercon-ducting wires released from several companies, and itcurrently achieves Ic of more than 200 A (at 77 K underself-field) in a width of approximately 4 mm. This Ic

value is the world record for highest Ic achieved by apractically used superconducting wire (3).

The specifications of the superconducting wireused for the coils are shown in Table 2. This supercon-ducting wire has a tape shape with an aspect ratio asshown in the table. The wires having Ic of more than120 A (at 77 K under self-field) were adopted for the

coils. The superconducting wire shows higher Ic inlower temperatures, and Ic at 68 K may be around 1.6

times higher than Ic in liquid nitrogen temperature. Anarmature coil consisted of several double pancake coilseach made by winding a superconducting wire in thecircumferential direction (Fig. 2). The coil inductanceand operating current were adjusted to suitable valuesso that the coils can be driven by a general-purposeinverter.

The amplitudes of magnetic field and electromag-netic force applied to the superconducting wire and thecoils thermal design should be taken into considerationin designing a coil. These were investigated in details bymeans of experiments on an actual motor model.

3-2 Magnetic field dependence of superconducting

properties

The Ic value of a superconducting wire decreaseswhen a magnetic field is applied. When a magnetic field

is applied to the surface of a tape in a perpendiculardirection, Ic decreases more drastically than in the casewhere a parallel magnetic field is applied. This behavioris an essential nature of superconductors and must beconsidered when designing a superconducting coil.Figure 3 shows the Ic-B characteristics of a DI-BSCCO

wire at 68 K. The straight line in the figure is the loadline of the coil indicating the relationship between mag-netic field and operating current. A coil should bedesigned in a way that the operating current is not high-er than the current at the intersection of the Ic-B curveand the load line. The operating current of the arma-ture coil of the motor drive was decided with the maxi-

mum magnetic field applied perpendicularly to the tapesurface taken into consideration.

42 Development of Superconducting Coil for Ship Pod-Propulsion Motors

Table 2. Typical specifications of BSCCO wire adopted in HTS coil

Critical current (77K, self-field)

Width

Thickness

Length

HTS Coil

Permanent Magnet

Fig. 1. Structure of 400-kW permanent magnet HTS motor

Double pancake coil

Stack

Fig. 2. Schematic diagram of HTS coil

Allowable tensile strength (RT)

Allowable tensile strength (77K)

Allowable bending diameter (RT)

>120 A

100 MPa

135 MPa

70 mm

4.20.2 mm

0.220.02 mm

1500 m max.


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3-3 Electromagnetic force applied to superconduct-

ing wireA magnetic field is induced by conducting electrici-

ty to an HTS coil. Because of the Lorenz force that isgenerated by a current and a magnetic field, a coil isunder a compressive stress in the axial direction (thedirection double pancake coils are stacked) and a hoopstress in the radial direction. Therefore, HTS coils needto be designed to sufficiently withstand these stresses.Figure 4 shows the compressive stress distribution of theHTS coil in the axial direction. The stress balanceoccurs at the center of the coil, therefore the coil is notmoved by the stress. However, the superconducting wirelocated in the coil center is under the maximum com-

pressive stress. The durability of the HTS coil against thecompressive stress was tested using a double pancakecoil made for experimental purpose. The test result con-firmed the fine durability of the coil, showing that thefracture resistance of the coil was higher than the elec-tromagnetic compressive stress by two digits. Figure 5 isthe distribution of the hoop stress applied to the coil.The hoop stress is the stress that causes the coil to

expand in the radial direction, and the tensile stress isapplied to the superconducting wire in the longitudinaldirection of the wire. The vertical axis of Fig. 5 showshoop stress converted to longitudinal tensile stress. TheDI-BSCCO wire, which was manufactured using the CT-OP process as mentioned previously, was used in assem-bling the coil and has not only high Ic but alsoimproved mechanical properties compared with con-

ventional superconducting wires. Table 2 shows that DI-BSCCO has the tensile strength of more than 100 MPaat both room temperature and 77 K, the value highenough to withstand the strain applied to it due to theelectromagnetic force.

3-4 Heat design of HTS coil

Losses do not occur when HTS coils are operatedwith DC currents, but AC losses are generated whenoperated with AC currents. AC losses can be roughlydivided into hysteresis losses, coupling losses and eddycurrent losses. The predominant AC loss in an HTS coilis hysteresis loss. In the stage of coil design, it is neces-sary that the hysteresis loss is estimated and the temper-ature rise is calculated so as to prevent the occurrenceof thermal runway. The hysteresis loss of an HTS coilcan be calculated from the alternating magnetic fieldand the current applied to the wire (4).

The calorimetric measurement using liquid nitro-gen was carried out to assess the heat generation of theHTS coil due to AC losses. Figure 6 shows the schematicdiagram of the experimental setup. The HTS coil isplaced in the inner container of a double-containercryostat. The inner and outer containers were filled withliquid nitrogen. A tube was installed to the inner con-tainer to collect vaporized nitrogen, and a gas flowmeter was equipped to the tube to measure the flow vol-ume of vaporized nitrogen. By measuring the flow vol-ume per unit time of vaporized nitrogen and obtainingthe latent heat of liquid nitrogen, the heat release value


200

180

160

140

120

100

80

60

40

200

0 0.2 0.4 0.6 0.8 1

Magnetic Field (T)

CriticalcurrentIc(A)

Parallel to tape surfacePerpendicular to tape surfaceLoad line

Fig. 3. Magnetic field characteristics of BSCCO wire at 68 K

0

0.02

0.04

0.06

0.08

0.1

0.120.14

0.16

0.18

Double pancake coil No.

Compressivestress(M

Pa)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Fig. 4. Distribution of axial compressive stress applied to HTS coil

0

0.1

0.2

0.3

0.4

0.5

0.8

0.7

0.6

Double pancake coil No.

Hoopstress(MPa)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Fig. 5. Distribution of hoop stress applied to HTS coil

Current lead

Inner container

coil

N2 gas

Liquid N2 Outer container

Gas flow meterPower supply

Fig. 6. Experimental setup for calorimetric measurement of liquid nitrogentemperature


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of the HTS coil is estimated. The experiment resultsobtained using the calorimetric method and the theo-retical values are shown in Fig. 7. The good agreements

were observed between the experimental and estimatedvalues. The results of the AC loss experiments werereflected in the refrigeration system of the PM-HTSmotor.

4. Fabrication and tests of 400-kW PM-HTSmotor

4-1 Fabrication of armature coilThe double pancake coils fabricated for the arma-

ture coils of the 400-kW PM-HTS motor are targeted foruse in civilian applications. Therefore, the manufactur-ing process of the coils was managed by implementing

an appropriate quality control procedure. The qualitiesof materials and the Ic value, inductance and inner andouter diameters of coils were controlled completely fol-lowing the flow chart shown in Fig. 8. A total of 270 dou-ble pancake coils including those for experimental use

were fabricated. The system for fabricating coils was con-structed under the aforementioned quality control sys-tem, and it took less than a month to fabricate all coils.

4-2 Test results of PM-HTS motor (2)

A PM-HTS motor equipped with the abovedescribed armature coils made by Sumitomo Electric

was tested under no-load conditions. The torque andcurrent characteristics of the PM-HTS motor was evalu-ated by a locked rotor test. When an AC current of 540

A was sent into the coil, the torque of the motor was14.5 kN. This result corresponds with a 380 kW outputat 250 rpm. In this test, because of the problems of thetest facilities, the maximum current was limited to 540

A. However, the current-torque curve obtained as a testresult analytically demonstrated that the motor canachieve an output of 400 kW. The acceleration anddeceleration tests were also performed, and the testresults confirmed that the motor achieves smooth accel-eration and deceleration.

5. Conclusions

A 400-kW PM-HTS motor for pod-propulsion sys-tems for ships was developed by an industry-universitycollaborative research group, and this prototype motorproved that it is technically feasible to achieve an outputof 400 kW. The Ic value of DI-BSCCO used for coil wind-ings is increasing year by year, and it should contributeto the increase of the output of the PM-HTS motor.

While it is important to enhance motor output, con-sidering that pod-propulsion systems will be introducedto the means of transportation such as ships and vesselsin near future, it is also important to achieve the long-term reliability of motor systems and individual deviceslike armature coils. For example, it is assumed thatoceangoing ships need to be maintenance-free for along period of time. The authors believe that the futuretechnical development of the PM-HTS motor should benot only in the improvement of motor output but also

in the long-term system reliability.

6. Acknowledgement

The authors are grateful to Professor H. Sugimotoof the University of Fukui for his guidance and helpfulcomments on the structure of the PM-HTS motor andto Mr. T. Takeda, Mr. H. Togawa and Mr. T. Ohta ofIHI Corporation for their cooperation in assessing theperformance of the HTS coils.

44 Development of Superconducting Coil for Ship Pod-Propulsion Motors

inputting ofmaterials

wire coiling

inspectionbefore resinimpregnation

resinimpregnation

inspectionafter resin

impregnation

inputting ofmaterials for coil

construction

constructionof coil

shippinginspection

Fig. 8. Flow chart for constructing HTS coil

100

Peak value of AC current (A)

ACloss(W)

10

110 100

16.7Hz experiment25.05Hz experiment33.4Hz experiment16.7Hz caliculation25.05Hz caliculation33.4Hz caliculation

Fig. 7. Results of calorimetric AC loss measurements


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References

(1) Sugimoto, Hondou, Akita, Nishikawa, Tsuda, Tsuji, Okazaki,

Ohashi; Presented at the Institute of Electrical Engineers of Japan

conference 2005, Tokushima University

(2) H. Sugimoto, T. Tsuda, T. Morishita, Y. Hondou, T. Takeda, H.

Togawa, T. Oota, K. Ohmatsu, S. Yoshida; IEEE Trans. Appl.

Supercond., Vol.17, pp.1637-1640, 2007

(3) Ayai, Kikuchi, Yamazaki, Yamade, Hata, Sato, Hayashi, Kato,

Fujikami, Kobayashi, Ueno, Fujino; SEI Technical Review, p.103,

No.169 (2006)

(4) M. Iwakuma, Y. Fukuda, M. Fukui, K. Kajikawa, K. Funaki; Physica

C: Superconductivity, Volumes 392-396, 2003, Pages 1096-1101


Contributors (The lead author is indicated by an asterisk (*)).

K. FUJINO*

Assitant General Manager, Application Group, Superconductivity & Energy Technology Department

T. HAYASHI

Dr. Eng., Application Group, Superconductivity & Energy Technology Department

T. SANAMI

Application Group, Superconductivity & Energy Technology Department

K. HISADA

Advanced Production Systems Engineering Department, Plant & Productin Systems Engineering Division

K. OHMATSU

Manager, Application Group, Superconductivity & Energy Technology Department

T. OKAZAKI

Ph. D., Assitant Manager, Application Group, Superconductivity & Energy Technology Department

desarrollo de superconductores para motores de propulsion

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