development of superconducting magnetic bearing capable of

281QR of RTRI, Vol. 59, No. 4, Nov. 2018

Katsutoshi MIZUNOYoshiki MIYAZAKI

Development of Superconducting Magnetic Bearing Capable of Supporting Large Loads in Flywheel Energy Storage System for Railway Applications

Cryogenic Systems Laboratory, Maglev Systems Technology Division

Tomohisa YAMASHITAMaglev Systems Technology Division

Kengo NAKAO

A superconducting magnetic bearing (SMB) has been developed with high temperature superconducting (HTS) coils and bulks for a flywheel energy storage system (FESS). The FESS equipped with the SMB was tested at the mega photovoltaic power plant test site in Ya-manashi Prefecture. The SMB with both rotor and stator made of superconducting material, was capable of supporting the flywheel weighing 4000 kg without any contact and has so far remained in stable operation for 5000 hours. A further increase in storage capacity is required for the FESS to be applicable to railways as a system for preventing cancellation of regenera-tive braking. This paper describes the development of a SMB capable of supporting large 147 kN loads using a new type coil structure for the improvement of FESS storage capacity.

Keywords: flywheel, energy storage system, high temperature superconducting magnetic bearing, railway application, large load

1. Introduction

A FESS using SMB consisting of HTS coils and bulks, capable of suspending large loads stably without any con-tact has been developed [1]. The SMB, which is a contact-less bearing, enables better maintainability which is the key problem faced with conventional flywheels because of conflict between bearings and mechanical losses. Flywheels using SMB have been under trial at the Komekurayama photovoltaic power test plant located in Kofu City, Ya-manashi Prefecture since 2015 as a means to smooth elec-trical power output fluctuations in order to achieve a more stable power supply (Fig. 1, 2) [2]. The flywheel using SMB remained levitated for more than 5000 hours including plant tests, confirming the high reliability of SMB. Current trials are testing the reliability of SMB in experiments where they are subjected to 100 excitation cycles and 24 cooling cycles [3]. If FESS using SMB is to be applied to the railways to prevent cancellation of regenerative brak-ing, the load that the SMB can supported must be raised, in order to increase storage capacity. This paper therefore reports on the design of a new superconducting coil fixed with a thermoplastic resin proposed by Railway Technical Research Institute, and the results of SMB levitation tests.

2. Underlying principles and characteristics of a su-perconducting flywheel energy storage system

Flywheel energy storage systems can store electricity in the form of kinetic energy by rotating a flywheel and

converting the kinetic energy to the electric energy again on demand. A FESS does not deteriorate in the way of chemical cells due to repeated charging and discharging. Consequently, a FESS can be employed as a long-life stor-age system for applications requiring high frequency charg-ing / discharging. For example, for an expected serviceable life of 30 years, the FESS must withstand several million or more charge/discharge cycles in order to effectively uti-lize the regenerative energy produced by electric railways or to moderate electrical power fluctuations from renew-able energy sources, such as photovoltaic and wind power plants. As such, FESS is considered to be an option for such applications. The principles underlying a FESS are shown in Fig. 3. The stored energy E [J] can be expressed in the following equation, where M [kg] is the weight and r [m] is the radius of the flywheel rotor, ω [rad/sec] is the

Shinichi MUKOYAMA Furukawa Electric Co., Ltd.

Taro MATSUOKA Furukawa Electric Co., Ltd (previous company).

Fig. 1 Overview of test facilities for prototype FESS

Fig. 1 Overview of test facilities for the prototype FESS

Mt. Fuji

Komekurayama photovoltaic power plant located in Kofu City, Yamanashi Prefecture

Test facilities

FESS with SMB

prototype

PAPER

282 QR of RTRI, Vol. 59, No. 4, Nov. 2018

rotation angular velocity.

E M r=14

2( )ω (1)

Table 1 compares secondary batteries, capacitors and conventional flywheels. Since the output power and the storage capacity of secondary batteries and capacitors are closely related, they cannot be freely designed. On the other hand, the output power and the storage capacity of a FESS can be designed independently according to purpose because the storage capacity is defined from (1), and the output power is determined from the motor generator pow-er. Furthermore, a FESS has the advantage that the rest of the storage capacity can be checked easily by monitoring the number of rotations, and if the rotation stops, the stor-age energy drops perfectly to zero. However, the large loads to be supported by the bearing in conventional FESS with mechanical bearings generates the need for large-scale maintenance. Based on this, a FESS would be inferior in

Fig. 2 System configuration of prototype FESS

Fig. 4 HTS coils and bulks constituting SMB

Fig. 3 Schematic representation of FESS operating prin-ciples

Fig. 2 System configuration of prototype FESS

Superconducting magnetic bearing

（in the inner vessel）

Motor generator

Magnetic fluid seal

Thermal insulation shaft

Vacuumvessel

CFRP flywheel

Generator mode

Motor modeCharge

Discharge

Motor Generator

Flywheel

Kinetic energy

Electric energy

Converter

Time

Num

ber o

f ro

tatio

nsFl

ywhe

el

mod

e

3

Flywheel energy storage systems can store theelectricity in the form of the kinetic energy from theelectric energy by rotating a flywheel, and convertthe kinetic energy to the electric energy again byneed. The FESS dose not deteriorate due to therepeated charge and discharge like chemical cells,therefore the FESS is expected as a long lifestorage system for applications requiring highfrequency charging / discharging. For example, ifthe expected life is 30 years, in order to effectivelyutilize the regenerative energy of the electricrailway and to moderate the electrical powerfluctuation of the renewable energy such asphotovoltaic and wind power generation, it isnecessary to cope with the several million times ormore charging / discharging cycle. The FESS isalso considered to be one of the options for suchapplications. The principle of the FESS in Fig. 3.the storage energy E [J] can be designed asfollowing equation, where M [kg] is weight and r[m] is the radios of the flywheel rotor, ω [rad/sec] isthe rotation angular velocity.

Fig. 3 Schematic representation of FESS operating principles

Table 1 Comparison between various types of batteriesItem Rechargeable

BatteriesCapacitor Flywheel

Charge rate △ ○ ○

Storage volume ○ △ ○

Discharge rate △ ○ ○

Maintainability ○ ○ △

performance to secondary batteries or capacitors from a maintenance point of view. The solution to this problem is the SMB developed by RTRI where a strong magnetic repulsion force is used to levitate the flywheel eliminating contact and mechanical loss.

3. Results of experiments

3.1 Subheading limited to one line as much as pos-sible

Figure 4 shows the HTS coils and bulks constituting the SMB. When the coils are excited, a powerful mag-netic field is generated at the center of the coils. Then, the shielding current circulates across the surface of the HTS bulks, and a strong magnetic repulsive force is generated between the HTS coils and bulks. The SMB can support the weight of the flywheel rotor taking advantage of this force. HTS bulks in a rotor consist of one with a diameter of 140 mm and 20 mm thick, and two bulks 90 mm in di-ameter and 20 mm thick. The HTS bulks were manufac-tured by NIPPON STEEL & SUMITOMO METAL using the QMG (Quench and Melt Growth) method in such a way as to form a large disk [4, 5]. The HTS bulk with a diam-eter of 140 mm in the rotor supports the thrust load, while the two HTS bulks with a diameter of 90 mm function as a guide in the radial direction. The HTS coil as the stator is composed of five layers of double-pancake coil made with tape-shaped rare-earth HTS wires (manufactured by Super-Power) 6 mm in width and 0.1 mm thick coiled in the shape of a pancake with an outer diameter of 260 mm and inner diameter of 120 mm. Table 2 shows the design parameters of the HTS coil. To prevent the eddy current accompanying rotation, a “bamboo screen” structure cupper plate molded from thermoplastic resin is used for the cooling plate of the coils close to the HTS bulks [6]. Figure 5 shows the basic components in the SMB. The HTS coils are connected to a cryocooler and the HTS bulks are in a rotor. Helium gas is used to fill the inner vessel containing the SMB, and the pressure of the gas is designed to be in the pressure region (about 10 Pa) where the gas friction resistance (windage drag) is sufficiently small while heat transfer is large [7]. The HTS coils can be conductively cooled down while the HTS bulks are cooled by the helium gas. Therefore, it is a simple system that does not need a cryogen such as liquid nitrogen.

Fig. 4 HTS coils and bulks constituting the SMB

5

HTS bulks

140 mm

90 mm

120 mm

260 mm

20 mm

HTS coils

Levitation gap20 mm

No. 1

No. 2

No. 3

No. 4

No. 5

高温超電導バルク

140 mm

90 mm

120 mm

260 mm

20 mm

高温超電導コイル

浮上ギャップ20 mm

No. 1

No. 2

No. 3

No. 4

No. 5

Fig. 4 shows the high temperature superconducting coils and bulks constituting the SMB. When the coils are excited, a largemagnetic field is generated near the coils. Then, the shielding current is circulated in the high temperature superconductingbulks, and the strong magnetic repulsive force is generated between the high temperature superconducting coils and bulks. TheSMB can support the weight of the flywheel rotor taking advantage of this force. REBCO HTS bulks in a rotor consist of one 140mm diameter with 20 mm thick and two 90 mm diameter bulks with 20 mm thick. REBCO HTS bulks made by Nippon SteelSumikin is produced by the QMG method shaped as a large disk. High temperature superconducting bulk is one in which alarge single crystal body is fabricated from the second generation high temperature superconducting material by the QMGmethod and is shaped into a disk shape. The rotor has one HTS bulk with 140 mm in diameter which supports the thrust load,and two HTS bulks with 90 mm in diameter function as a guide in the radial direction. The high-temperature superconductingcoil as the stator is a 6 mm in width and 0.1 mm in thickness, which is made of a tape-shaped rare-earth high-temperaturesuperconducting wire (manufactured by SuperPower) coiled to a size of 260 mm in outer diameter and 120 mm in innerdiameter as a stacked in 5 layers.Table 2 shows design parameters of the high-temperature superconducting coil. A cooling plate is sandwiched between eachdouble pancake coil, and the cooling plate of the coil close to the superconducting bulk is made of a thermoplastic resin ("lowheat generating copper interdigital material") for the purpose of suppressing eddy current heat generation accompanyingrotation, Fusion bonding material) was used.


3.2 New HTS coils fixed with thermoplastic resin

Given that the storage capacity of the FESS for appli-cation to railways must be in the tens of kWh, it is impor-tant to be able to change the load supported by the SMB from 39.2 kN (as in the Komekurayama prototype) to 147 kN. A new coil was therefore designed and built, and fixed with a thermoplastic resin which can obtain a high cur-rent density and produce a large levitation force due to the improved winding space in the coils compared to conven-tional designs, and a test to verify the levitation force was conducted [8, 9]. Figure 6 shows the cross sectional areas of the new type coil component (b) compared to the conven-tional design (a). The conventional coil design used for the Komekurayama prototype (Fig. 6 (a)), has a double pan-cake coil encased in glass-fiber reinforced plastic (GFRP) plate, and cooling plates are attached to the upper and lower sides. The heat transfer path is a high temperature superconducting wire - GFRP - cooling plate, and contact is maintained with each surface with compressive loads. In order to obtain more stable cooling, the cooling plate and the HTS wire should be fixed without inserting a thermal insulating layer such as GFRP between them. Therefore, the new coil design introduces a design which is the result of a developed actual HTS coil for Maglev. This means that the GFRP plate on the upper and lower surfaces of the conventional coil were replaced with a meshed copper plate while the HTS wire and the cooling plate were fixed with a thermoplastic resin to improve heat conductivity (Fig. 6 (b)) [10, 11]. In order to prevent the deformation and movement of the HTS wire, thermoplastic resin was also used for the GFRP plate in the coil. In the new coil structure, the gap between the double pancake coils was made smaller than in the conventional coil design, to make the coil structure compact and to obtain a high current density, i.e. generate a powerful levitation force.

3.3 Load tests using small-scale coil

In order to verify the manufacturability and load ca-pacity of the new coil design, small-scale coils were pro-duced for preliminary tests [8]. The specifications of the

Table 2 Design parameters of HTS coilHTS wire RE-Ba-Cu-OWidth of wire 6 mmThickness of wire 0.1 mmInner diameter of coil 120 mmOuter diameter of coil 260 mmThickness of double pancake coil 17.6 mmNumber of double pancake coil 5Inductance of coils 4 H

Fig. 5 Basic component of SMB

Fig. 5 basic component of the SMB

6

HTS coils(stator)

HTS bulks(rotor)

Cryocooler

Inner vessel

Diluted gas helium

高温超電導コイル(ステータ)

高温超電導バルク(ロータ)

冷凍機

内槽容器

希薄ガスヘリウム

Fig. 5 shows the SMB basic component. The REBCO HTS coils connected to a cryocooler and REBCO HTS bulks are in a rotor. Gas helium is filled in the inner vessel containing the SMB, the pressure of the gas is designed to be a pressure region (about 10 Pa) where the gas friction resistance (windage loss) is sufficiently small and the heat transfer is large. The HTS coils can be conductively cooled down and the HTS bulks were cooled by the helium gas. Therefore, it is a simple system that does not use cryogen like liquid nitrogen.

small-scale coil were 60 mm in inner diameter, 96 mm in outer diameter and 124 in number of turns, and SCS 6050-AP (6 mm wide wire made by SuperPower Co., Ltd.) was used for the HTS wire. The critical current (Ic) of the small-scale coil was measured in liquid nitrogen. In order to confirm that there was no deterioration in the coil dur-ing the production process, the coil was excited before and after the thermoplastic resin fixation process. After check-ing the coil, a load test was carried out with a compression tester. Figure 7 shows the schematic illustration of the compression test. The compression test was conducted with the coil excited, and the voltage change between both the ends of the coil was measured. A new coil design fixed with the thermoplastic resin and using the same specifications as the Komekurayama prototype was selected, based on the following confirmations: Namely, no change in critical current due to compressive loads and no damage to the structural members, improvement of cooling by copper interdiction material, no significant change in the critical current of the superconducting coil even under a load of 50 kN (same level as the Komekurayama prototype), and no visible damage.

Fig. 6 Cross sectional areas of new type coil component (b) compared to conventional design (a)

図６

7

2段組図幅

(b) New HTS coil fixed with thermoplastic resin

(a) Conventional HTS coil

double pancake coil

Cooling plate GFRP plate

Cooling plate GFRP plate

double pancake coil

HTS wire

HTS wire

(b) 熱融着材法を適用した新型コイル構成

(a) 従来型のコイル構成

ダブルパンケーキコイル

冷却板 GFRPプレート

冷却板 GFRPプレート

ダブルパンケーキコイル

高温超電導線材

高温超電導線材

Since it seems to be necessary that the storage capacity is tens of kWh to apply the FESS to the railwayfield, it is important that the load supported by the SMB changes from 39.2 kN in the Komekurayamaprototype range to 147 kN. We designed and fabricated a new coil structure using fusible material methodwhich can obtain high current density and large levitation force due to the improvement of the windingspace factor of the coils compared with the conventional types, and verified levitation force verification testwas conducted. Fig. 6 shows the cross sectional areas of the new type coil component (b) compared to theconventional one (a). In the conventional coils used for the SMB of the Komekurayama prototype (Fig. 6(a)),The double pancake coil is casing with a glass fiber reinforced plastic (GFRP) plate, and a coolingplate is attached on the upper and lower sides. The heat transfer path is a high temperature

HTS wire

Fig. 7 Schematic illustration of compression test

図７

8

Small-scale coil

For verifying the manufacturability and load capacity of the new typecoils, we made a small scaled coil and carried out the pre-tests.The specification of the small scaled coil is 60 mm in inner diameter,96 mm in outer diameter and 124 in number of turns, and SCS 6050-AP (6 mm width wire made by SuperPower Co., Ltd.) is used for hightemperature superconducting wire. The critical current (Ic)measurement of small scaled coil was carried out in liquid nitrogen. Inorder to confirm that there was no deterioration in the coil during themaking process, the coil was excited before and after thethermoplastic resin process. After checking the coil, a load test wascarried out by a compression tester. Fig. 7 shows the schematicillustrates of the compression test. The compression test is conductedwith the coil excited, and the change of the voltage between the bothside of the coil was measured. We decided to develop a new typesuperconducting coil by the fusing material method of the samespecification as the komekurayama prototype based on the followingconfirmation. Namely, no change in critical current due tocompressive load or no damage of the structural members,improvement of cooling by copper interdiction material, no significantchange in the critical current of the superconducting coil even whenexperienced a load of 50 kN (same level as the komekurayamaprototype), and no damage on the appearance.

Cooling plate

Hydraulic cylinders

Compression jigLiquid

nitrogen container

4. Levitation force test [12]

4.1 Coil configuration and load factor prediction

In designing the new coil fixed with the thermoplastic resin, the arrangement of the wires to be used was exam-ined so that the load factor during the excitation was at most 60%. From the electromagnetic force analysis, when the exciting current of the HTS coil was 160 A, the levi-


tation force was 147 kN. Figure 8 shows the load factor distribution predicted at a coil temperature of 30 K and ap-plied current of 160 A. The upper two coils (No. 1 and No. 2) were built by connecting short wires, and the wire having a high critical current was positioned where the load fac-tor was high. Therefore, the load factor was kept low, 0.6 at the maximum (the innermost periphery of the double pancake coil of the 2nd and the 3rd layer), and it was con-firmed that excitation can be performed with a sufficient margin at 30 K. Based on the above discussion, the latest rare-earth HTS wire (Ic: 200 A or more at 77 K manufac-tured in 2016 to 2017) was used for the three coils on the HTS bulk side from among the five double pancake coils. A new coil fixed with the thermoplastic resin was built, and levitation force verification tests were carried out.

4.2 Levitation force test exceeding 147 kN

Figure 9 shows the appearance of the new coil fixed with the thermoplastic resin, and Fig. 10 shows the ex-perimental setup of the levitation force test. The levitation force generated between the HTS coils and bulks was mea-sured by a load cell installed on the upper part (atmosphere side) of the test apparatus. The thermal insulation shaft with the built-in HTS bulk had the same specifications as the Komekurayama prototype and was subjected to a levitation force of 98 kN. The repulsive force between the HTS coil and the bulk was supported by the outer vessel container via four thermal insulation supports, described later. In the dilute helium gas atmosphere, the HTS coils and bulks were brought to the predetermined temperature by the cryocooler, and then the HTS coils were excited. Fig-ure 11 shows the relationship between the excitation cur-rent and the generated levitation force, together with that obtained from the calculation and that at the time of the 98 kN test. The levitation force was in equilibrium with the atmospheric pressure load (0.93 kN) when the applied current exceeded 25 A, and in the region above 25 A, the levitation force increased almost by the square of the ap-plied current, and the levitation force of the target value of 147 kN was obtained when the applied current was 160 A. The reason for the difference with the calculated value was considered to be the influence of the magnetic flux penetra-tion into the HTS bulks. After the levitation test, a visual check of the HTS bulk and an excitation test of the single coil were carried out, which confirmed that there was no change in the HTS coil characteristics. It is deemed that these results prove that the SMB for large load using the new HTS coils fixed with thermoplastic resin, are suitable for manufacture.

5. Thermal insulation supports

The appearance of the thermal insulation supports is shown in Fig. 12. Since the thermal insulation support transmits the levitation force applied to the low-temper-ature vessel of the SMB to the part at room temperature, compatibility between the thermal insulation properties and the load bearing characteristics is necessary. For this reason, alumina fiber reinforced plastic (AFRP), which has excellent thermal insulation properties and high tensile

Fig. 8 Load factor distribution predicted at coil tempera-ture of 30 K

Fig. 10 Experimental setup of levitation force test

Fig. 9 Internal structure of HTS coil and appearance of new coil design fixed with thermoplastic resin

Fig. 11 Relationship between excitation current and gen-erated levitation force

図８

9

Double pancake coil No. 1

No. 3 coil was manufacturedby connected wire(700 m)

The upper two coils (No. 1and No. 2) are manufacturedby connecting short wirerods(Ic@77 K: 200 ~ 260 A)

0.6

0





HTS bulk side

ダブルパンケーキコイルNo. 1

接続済み線材(700 m強)で巻線

負荷率予測に基づいて、短尺の線材を接続しつつ巻線(Ic@77 K: 200 ~ 260 A)

0.6

0





高温超電導バルク側

Load factor distribution diagram of HTS coil

coilwas

beat

%.analysis,

high-A,

thecoil

of2)

wirehavingwhere

loadmaximum

doublerd

thatsufficient

latestsuperconducting

manufacturedcoilsbulkWe

usinga図９

10

Fig. 9 shows the appearance of a new coil to whichthe fusing material method is applied, and Fig. 10shows the schematic configuration of the levitationforce verification test apparatus.

Internal structure of HTS coil and appearance of new type coil fixed with the thermoplastic resin

Fig. 11 Relationship between the excitation current and the generated levitation force

12

Levi

tatio

n fo

rce

[kN

]

Excitation current [A]

0

20

40

60

80

100

120

140

160

0 50 100 150 200

98 kN 試験時

147 kN 試験時

計算値

Fig. 11 shows the relationship between theexcitation current and the generated levitationforce, together with the calculated value, atthe time of the 98 kN test. The levitation forceis in equilibrium with the atmosphericpressure load (0.93 kN) when the appliedcurrent exceeds 25 A, and in the region above25 A, the levitation force increases almost bythe square of the applied current, and thelevitation force of the target value of 147 kNwas obtained when the applied current was160 A. The difference from the calculatedvalue is considered to be the influence of themagnetic flux penetration into the hightemperature superconducting bulk. After thelevitation test, the appearance check of thesuperconducting bulk and the excitation testof the single coil were carried out, and it wasconfirmed that there was no change insuperconducting coil characteristics. From theabove, we believe that it is proved that theSMB for the large load by newsuperconducting coil applying fusible materialmethod can be constructed.

calculated value

Experimental (147 kN)

Experimental (98 kN)

Fig. 10 Experimental setup of the levitation force test

0

Thermal insulation

shaft

HTS coils

New coil

Conventional coilConventional coil

New coilNew coil

Inner vessel

Thermal insulation supportsLoad cell

Levitation force

HTS bulks


strength, was adopted. When the levitation force was 147 kN, the reaction force of each thermal insulation support was 36.8 kN. After confirming that the thermal insulation support could be used in an elastic deformation region up to 98 kN with a safety factor of more than 2 [13], the ther-mal insulation supports were incorporated into the levita-tion force test apparatus. Figure 13 shows the state of the tensile test of the thermal insulation support. The strain gauge was attached in the center of the AFRP rod. Figure 14 shows the tensile test results of the thermal insulation support before and after the levitation force tests. When the maximum tensile force was 49 kN, the elastic modu-lus of the AFRP was about 42 GPa as seen from the stress strain diagram and the maximum stress of the tensile test was 110 MPa. It was confirmed that the characteristics of the thermal insulation support did not change even after the levitation force test of 147 kN [14]. Basic data will be collected on the reliability of the thermal insulation sup-port, which is an important component of the SMB, by evaluating the strength (fracture strength) of the AFRP rod and repeated tensile load tests corresponding to the SMB’s expected life of 30 years. 6. Conclusions

Given that the storage capacity of the FESS for appli-cation to railways must be in the tens of kWh, it is impor-tant to be able to change the load supported by the SMB from 39.2 kN (as in the Komekurayama prototype) to 147 kN. A new HTS coil design was therefore developed, fixed with thermoplastic resin, drawing on the results from de-velopment work on actual sized HTS coils for Maglev, and SMB levitation force tests were conducted. The new HTS coil was incorporated into levitation force test apparatus; the HTS coils and bulks were then brought to the prede-termined temperature by the cryocooler, and the super-conducting coil was excited. The target 147 kN levitation force was obtained when the current applied was 160 A. After the levitation test, a visual inspection of the super-conducting bulk and excitation tests on a single coil were carried out, confirming that there was no change in the superconducting coil characteristics. These results seem to prove the constructability of the SMB for large loads us-ing the new superconducting coil fixed with thermoplastic resin. The thermal insulation support was also designed to be capable of bearing a large load of 147 kN. The thermal insulation supports were incorporated into the levitation force test apparatus and subjected to levitation force tests. Tensile load tests were carried out before and after the lev-itation force tests confirming that there were no changes to the characteristics. The reliability of the SMB and the thermal insulation support will be further checked through repeated excitation tests, continuous levitation tests etc., to reflect actual operational conditions and assuming a ser-viceable life of 30 years.

Acknowledgements

This research was promoted with a view to effectively utilizing the results of progress made with the Kome-

kurayama prototype, which was subsidized by NEDO as part of the project entitled, “Development of Next Genera-tion Flywheel Power Storage System”. The “Development of a Superconducting Magnetic Bearing Able to support Large Loads in a Flywheel Energy Storage System for Railway Applications,” was made possible thanks to the generous cooperation of several companies including, Mi-rapro and Matsuikozai Co., Ltd. The authors would like to express their deepest gratitude to all parties involved in supporting this work.

References

[1] Nagashima, K., Seino, H., Miyazaki, Y., Arai, Y., Sakai, N. and Murakami, M., “Loading force density of a su-perconducting magnetic bearing using superconducting bulk body and superconducting coils,” RTRI Report, Vol.21, No.9, pp.29-34, 2007 (in Japanese).

Fig. 12 Appearance of thermal insulation supports

Fig. 13 State of tensile test on thermal insulation sup-ports

Fig. 14 Tensile test results for thermal insulation sup-ports

図12

13

Room temperature side flange

AFRProd

Low temperature side flange

The appearance of the adiabatic load supports is shown in Fig. 12. Since theadiabatic load supporting material plays a role of transmitting the levitation forceapplied to the low-temperature container of the SMB to the room temperature part,it is necessary to compatible both the heat insulating property and the load bearingcharacteristic. Due to this reason, alumina fiber reinforced plastic (AFRP) excellentin thermal insulation properties and tensile strength was adopted. When thelevitation force is 147 kN, the reaction force which the adiabatic load supportingmember takes is 36.8 kN respectively. After confirming that the adiabatic loadsupport material can be used in an elastic deformation region up to 98 kN with thesafety factor of more than 2. The adiabatic load support materials wareincorporated into a levitation force verification test apparatus.

図１３

14

strain gaugeAFRP rod

Flange

歪ゲージAFRPロッド部

フランジ部

Fig. 13 shows the state of the tensile test of the adiabatic load supporting material prototyped. The strain gauge was installed in the center of the AFRP rod.

図１４

15

Stre

ss[M

Pa]

Strain [%]

Before levitation force testAfter levitation force test

応力

[MP

a]

歪 [%]

浮上力検証試験前浮上力検証試験後

Fig. 14 shows the tensile test results of the adiabatic load support material before and after the levitation force verification test. When the maximum tensile force was 49 kN, the elastic modulus of AFRP was about 42 GPa from the stress strain diagram and the maximum stress of the tensile test was 110 MPa. It was confirmed that the characteristics of the adiabatic load support material did not change before and after the levitation force verification test of 147 kN.We plan to accumulate basic data on the reliability of the adiabatic load supporting material, which is an important component of SMB by the evaluation of strength (breaking load) of AFRP rod and repeated tensile load test corresponding to expected life 30 years.


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[6] Miyazaki, Y., Yamashita, T., Hasegawa, H., Arai, Y., Matsuoka, T., Nakao, K., Ishihara, T., Kaimori, H., Matsui, Y., Dohi, T. and Uejima, F., “Development of Superconducting Magnetic Bearing for flywheel energy storage system - Measures to Eddy Current Heating at HTS Magnetic Bearing -,” Abstracts of CSSJ Confer-ence, Vol.91, p.15, 2015 (in Japanese).

[7] Seino, H., Nagashima, K., Tanaka, Y. and Nakauchi, M., “Study of the magnetic bearing consisting of cou-pling of superconductors applicable to the support bearing of flywheel energy storage system,” RTRI Re-port, Vol.22, No.11, pp.35-40, 2008 (in Japanese).

[8] Mizuno, K., Yamashita, T., Miyazaki, Y., Sakamoto, H., Nakao, K., Matsui, Y., Dohi, T., “Enhance a maximum load of High Temperature Superconducting Magnetic Bearing - New type coil structure can balance low heat with cooling -,” Abstracts of CSSJ Conference, Vol.94, p.128, 2017 (in Japanese).

[9] Nakao, K., Sakamoto, H., Mizuno, K., Miyazaki, Y., Yamashita, T., “HTS magnetic bearing for heavy load (1) -New coil design using bonding process-,” Abstracts of CSSJ Conference, Vol.95, p.166, 2017 (in Japanese).

[10] Mizuno, K., Sugino, M., Ogata, M., “Experimental pro-duction and evaluation of racetrack coils for on-board REBCO magnet,” RTRI Report, Vol. 29, No. 11, pp. 11-16, 2015 (in Japanese).

[11] Mizuno, K., Sugino, M., Tanaka, M., Ogata, M., “Devel-opment of a real-scale REBCO coil for the demonstra-tion of magneto motive force of 700 kA,” RTRI Report, Vol. 31, No. 1, pp. 5-10, 2017 (in Japanese).

[12] Mizuno, K., Miyazaki, Y., Yamashita, T., Nakao, K., Sakamoto, H., Shimizu, H., Sawamura, H., Ozawa, K., Matsui, Y., Dohi, T., Uejima, F., “HTS magnetic bear-ing for heavy load (2) -Results of heavy load tests-,” Abstracts of CSSJ Conference, Vol. 95, p.167, 2017 (in Japanese).

[13] Miyazaki, Y., Yamashita, T., Mizuno, K., Matsui, Y., Dohi, T., Uejima, F., Asano, Y., Kazama, T., Nakao, K., Sakamoto, H., “HTS magnetic bearing for heavy load (3) -Test results of heavy load and reliability for ther-mal insulating support-,” Abstracts of CSSJ Confer-ence, Vol. 95, p.168, 2017 (in Japanese).

Authors

　　　　　

Yoshiki MIYAZAKI, Ph.D.Assistant Senior Research Engineer,Cryogenic Systems Laboratory, MaglevSystems Technology DivisionResearch Areas: Cryogenics andSuperconductivity

　　　　　

Katsutoshi MIZUNOAssistant Senior Research Engineer,Cryogenic Systems Laboratory, MaglevSystems Technology DivisionResearch Areas: Cryogenics andSuperconductivity

　　　　　

Tomohisa YAMASHITASenior Research Engineer, Maglev SystemsTechnology DivisionResearch Areas: Cryogenics andSuperconductivity

　　　　　

Kengo NAKAOResearch and Development Division,Furukawa Electric Co., Ltd.

　　　　　

Shinichi MUKOYAMA, Ph.D.Research and Development Division,Furukawa Electric Co., Ltd.

　　　　　

Taro MATSUOKAResearch and Development Division,Furukawa Electric Co., Ltd. (Previouscompany)

development of superconducting magnetic bearing capable of

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