Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Shigeru Yoshida Last modified date:2021.07.28

Professor / Office for the Promotion of Safety and Health


Papers
1. Shigeru Yoshida, Cryogenic cooling system for HTS cable, Progress in Superconductivity and Cryogenics (PSAC), 10.9714/psac.2017.19.2.001, 19, 2, 1-8, 2017.06, Recently, Research and development activity of HTS (High Temperature Superconducting) power application is very progressive worldwide. Especially, HTS cable system and HTSFCL (HTS Fault current limiter) system are proceeding to practical stages. In such system and equipment, cryogenic cooling system, which makes HTS equipment cooled lower than critical temperature, is one of crucial components. In this article, cryogenic cooling system for HTS application, mainly cable, is reviewed. Cryogenic cooling system can be categorized into conduction cooling system and immersion cooling system. In practical HTS power application area, immersion cooling system with sub-cooled liquid nitrogen is preferred. The immersion cooling system is besides grouped into open cycle system and closed cycle system. Turbo-Brayton refrigerator is a key component for closed cycle system. Those two cooling systems are focused in this article. And, each design and component of the cooling system is explained..
2. Masataka Iwakuma, Kizen Sakaki, Akira Tomioka, Takeji Miyayama, Masayuki Konno, Hidemi Hayashi, Hiroshi Okamoto, Yoshihiro Gosho, Tohru Eguchi, Shigeru Yoshida, Yoshiaki Suzuki, Hirokazu Hirai, Yasuhiro Iijima, Takashi Saitoh, Teruo Izumi, Yuh Shiohara, Development of a 3φ-66/6.9 kV-2 MVA REBCO superconducting transformer, IEEE Transactions on Applied Superconductivity, 10.1109/TASC.2014.2364615, 25, 3, 2015.06, We have designed and fabricated a 3φ-66 kV/6.9 kV-2 MVA transformer with RE
1
Ba
2
Cu
3
O
7-δ
(REBCO, RE:Rare Earth, Y, Gd etc.) superconducting tapes. It is a 1/10 model of a 3φ-66 kV/6.9 kV-20 MVA one for a distribution power grid. The superconducting windings were reduced only in current capacity by reducing the number of tapes in parallel conductors. In the primary side, a single REBCO tape with a width of 5 mm was cylindrically wound into 8 layers. In the secondary one, an 8-strand parallel conductor was wound similarly into 2 layers, where each strand was transposed 15 times per one layer. The REBCO tapes for the secondary winding were also scribed by laser into a 3-filament structure to reduce the ac loss. The windings for 3 phases were installed into a GFRP cryostat which had an elliptic-cylinder-shape and three cylindroid bore for an iron core at room-temperature. A Ne turbo-Brayton refrigerator with a cooling capacity of 2 kW at 65 K was developed and located close to the transformer. The windings were cooled with subcooled liquid nitrogen at 65 to 70 K, which was forced-flowed by a pump unit between the transformer and the refrigerator. The completed transformer was first tested in liquid nitrogen at 77 K according to the domestic regulation for conventional transformers. The load loss, i.e., ac loss of the windings, was 26.9 W for the rated operation. The dielectric strength was also verified by applying 350 kV impulse voltage and 140 kV ac voltage for 1 minute..
3. Shigeru Yoshida, Progress of cryogenic system for hts power transformer, Journal of the Institute of Electrical Engineers of Japan, 10.1541/ieejjournal.135.633, 135, 9, 633-636, 2015.01.
4. S.Yoshida, H.Hirai, N.Nara, S.Ozaki, M.Hirokawa, T.Eguchi, H.Hatashi, M.Iwakuma and Y.Shiohara, 1. Sub-cooled liquid nitrogen cryogenic system with neon turbo-refrigerator for HTS power equipment, Advances in Cryogenic Engineering, 59B, 1246-1253, 2014.06.
5. H.Hirai, .Hirokawa, S.Yoshida, T.Sano and S.Ozaki, Development of a turbine-compressor for 10 kW class neon turbo-Brayton refrigerator, Advances in Cryogenic Engineering, 59B, 1236-1241, 2014.06.
6. Hirai Hirokazu, Hirokawa Masaki, Shigeru Yoshida, Sano Tomonobu, Ozaki Shinsuke, Development of a turbine-compressor for 10 kW class neon turbo-brayton refrigerator, 2013 Joint Cryogenic Engineering and International Cryogenic Materials Conferences, CEC/ICMC 2013 Advances in Cryogenic Engineering - Transactions of the Cryogenic Engineering Conference - CEC, Volume 59, 10.1063/1.4860847, 1236-1241, 2014.01, We are developing 10 kW class turbo-Brayton refrigerator whose working fluid is neon gas. Its high pressure value is 1 MPa and its low pressure value is 0.5 MPa. The refrigerator consists of two turbine-compressors and a heat exchanger. The turbine-compressor has a turbo-expander on one side of its shaft and a turbo-compressor on the other side of the shaft. Two turbo-compressors are connected in series and two turbo-expanders are set in parallel. So, all amount of neon gas is compressed by two stages and each half a mount of neon gas is expanded by one stage. Two turbinecompressors are the same machines and development cost and time are minimized. In this stage, we made one prototype turbine-compressor and installed it in a performance test facility. This paper shows details of the turbine-compressor and refrigerator cooling power simulation results..
7. Shigeru Yoshida, H. Hirai, N. Nara, S. Ozaki, M. Hirokawa, T. Eguchi, H. Hayashi, Masataka Iwakuma, Y. Shiohara, Sub-cooled liquid nitrogen cryogenic system with neon turbo-refrigerator for HTS power equipment, 2013 Joint Cryogenic Engineering and International Cryogenic Materials Conferences, CEC/ICMC 2013 Advances in Cryogenic Engineering - Transactions of the Cryogenic Engineering Conference - CEC, Volume 59, 10.1063/1.4860849, 1246-1253, 2014.01, We developed a prototype sub-cooled liquid nitrogen (LN) circulation system for HTS power equipment. The system consists of a neon turbo-Brayton refrigerator with a LN sub-cooler and LN circulation pump unit. The neon refrigerator has more than 2 kW cooling power at 65 K. The LN sub-cooler is a plate-fin type heat exchanger and is installed in a refrigerator cold box. In order to carry out the system performance tests, a dummy cryostat having an electric heater was set instead of a HTS power equipment. Sub-cooled LN is delivered into the sub-cooler by the LN circulation pump and cooled within it. After the sub-cooler, sub-cooled LN goes out from the cold box to the dummy cryostat, and comes back to the pump unit. The system can control an outlet sub-cooled LN temperature by adjusting refrigerator cooling power. The refrigerator cooling power is automatically controlled by the turbo-compressor rotational speed. In the performance tests, we increased an electric heater power from 200 W to 1300 W abruptly. We confirmed the temperature fluctuation was about ±1 K. We show the cryogenic system details and performance test results in this paper..
8. H.Hirai, S.Yoshida, S.Ozaki, M.Hirokawa, K.Iwamoto, N.Nara, H.Okamoto, H.Hayashi and Y.Shiohara, Development of neon turbo-compressor with LN sub-cooler for HTS power equipments, Proceedings of the Twenty-Fourth International Cryogenic Engineering Conference and International Cryogenic Materials Conference 2012, 83-86, 2013.06.
9. Shigeru Yoshida, H. Hirai, N. Nara, T. Nagasaka, M. Hirokawa, H. Okamoto, H. Hayashi, Y. Shiohara, Consideration of sub-cooled LN2 circulation system for HTS power equipment, 2011 Joint Cryogenic Engineering and International Cryogenic Materials Conferences Advances in Cryogenic Engineering - Transactions of the Cryogenic Engineering Conference-CEC, 10.1063/1.4707097, 1649-1656, 2012.08, We consider a sub-cooled liquid nitrogen (LN) circulation system for HTS power equipment. The planned circulation system consists of a sub-cool heat exchanger (subcooler) and a circulation pump. The sub-cooler will be connected to a neon turbo-Brayton cycle refrigerator with a cooling power of 2 kW at 65 K. Sub-cooled LN will be delivered into the sub-cooler by the pump and cooled within it. Sub-cooled LN is adequate fluid for cooling HTS power equipment, because its dielectric strength is high and it supports a large critical current. However, a possibility of LN solidification in the sub-cooler is a considerable issue. The refrigerator will produce cold neon gas of about 60 K, which is lower than the nitrogen freezing temperature of 63 K. Therefore, we designed two-stage heat exchangers which are based on a plate-fin type and a tube-intube type. Process simulations of those heat exchangers indicate that sub-cooled LN is not frozen in either sub-cooler. The plate-fin type sub-cooler is consequently adopted for its reliability and compactness. Furthermore, we found that a cooling system with a Brayton refrigerator has the same total cooling efficiency as a cooling system with a Stirling refrigerator..
10. H. Hirai, M. Hirokawa, Shigeru Yoshida, N. Nara, S. Ozaki, H. Hayashi, H. Okamoto, Y. Shiohara, Neon turbo-brayton cycle refrigerator for hts power machines, 2011 Joint Cryogenic Engineering and International Cryogenic Materials Conferences Advances in Cryogenic Engineering - Transactions of the Cryogenic Engineering Conference-CEC, 10.1063/1.4707100, 1672-1679, 2012.08, We developed a prototype turbo-Brayton refrigerator whose working fluid is neon gas. The refrigerator is designed for a HTS (High Temperature Superconducting) power transformer and its cooling power is more than 2 kW at 65 K. The refrigerator has a turbo-expander and a turbo-compressor, which utilize magnetic bearings. These rotational machines have no rubbing parts and no oil-components. Those make a long maintenance interval of the refrigerator. The refrigerator is very compact because our newly developed turbo-compressor is volumetrically smaller than a displacement type compressor in same operating specification. Another feature of the refrigerator is a wide range operation capability for various heat-loads. Cooling power is controlled by the input-power of the turbo-compressor instead of the conventional method of using an electric heater. The rotational speed of the compressor motor is adjusted by an inverter. This system is expected to be more efficient. We show design details, specification and cooling test results of the new refrigerator in this paper..
11. H.Hirai, M.Hirokawa, S.Yoshida, N.Nara, S.Ozaki, H.Okamoto, H.Hayashi and Y.Shiohara, Neon turbo-Brayton cycle refrigerator for power machines, Advances in Cryogenic Engineering, 57, 1672-1679, 2012.06.
12. S.Yoshida, H.Hirai, N.Nara, T.Nagasaka, M.Hirokawa, H.Okamoto, H.Hayashi and Y.Shiohara, Consideration of sub-cooled LN2 circulation system for HTS power equipment, Advances in Cryogenic Engineering , 57, 1649-1656, 2012.06.
13. H.Hirai, M.Hirokawa, S.Yoshida, A.Takaike, S.Ozaki, N.Nara, K.Uwamori, Y.Kamioka, H.Okamoto, H.Hayashi and Y.Shiohara , Development of neon turbo-compressor with active bearings, Proceedinds of the Twenty-Third International Cryogenic Engineering Conference and International Cryogenic Materials Conference 2010 , 677-682, 2011.06.
14. S.Yoshida, N.Nara, K.Uwamori, S.Ozaki, H.Hirai, A.Takaike, M.Hirokawa, Y.Kamioka, H.Okamoto, H.Hayashi and Y.Shiohara, Development of neon refrigerator for HTS power machines, Proceedings of the Twenty-Third International Cryogenic Engineering Conference and International Cryogenic Materials Conference 2010 , 703-709, 2011.06.
15. H. Hirai, M. Hirokawa, Shigeru Yoshida, Y. Kamioka, A. Takaike, H. Hayashi, H. Okamoto, Y. Shiohara, Development of a neon cryogenic turbo-expander with magnetic bearings, 2009 Joint Cryogenic Engineering and International Cryogenic Materials Conferences Advances in Cryogenic Engineering - Transactions of the Cryogenic Engineering Conference-CEC, 10.1063/1.3422446, 895-902, 2010.06, A cryogenic turbo-expander with active magnetic bearings was made and tested in a reverse-Brayton cycle refrigerator using neon as working fluid. Turbine isentropic efficiency is a very important factor for the refrigerator since it affects the performance of the refrigerator significantly. Properties of neon are suitable for the working fluid in a refrigerator to cool HTS (High Temperature Superconducting) applications. The neon refrigerator needs a very small and high speed turbo-expander. But there are few studies of isentropic efficiencies of cryogenic turbo-expander using neon gas. Thus the experiment to get the design information was carried out. A prototype of neon refrigerator was made for HTS applications in 2007. Its cooling power was 2 kW at temperature of 70 K and operated in process pressure between 2 MPa and 1 MPa. To improve the performance of the neon refrigerator, the process pressure was changed to 1 MPa∼0.5 MPa. Under this process pressure, isentropic efficiencies for two types of turbine impellers were obtained. The test results were included in to the turbine design program so that we could predict the isentropic efficiencies of the turbo-expander more accurately. Details of the turbo-expander design and test results are described in this report..
16. Shigeru Yoshida, H. Hirai, A. Takaike, M. Hirokawa, Y. Aizawa, Y. Kamioka, H. Okamoto, H. Hayashi, Y. Shiohara, New design of neon refrigerator for HTS power machines, 2009 Joint Cryogenic Engineering and International Cryogenic Materials Conferences Advances in Cryogenic Engineering - Transactions of the Cryogenic Engineering Conference-CEC, 10.1063/1.3422275, 1131-1138, 2010.06, In 2007, we developed a prototype refrigerator with a small turbo-expander to provide adequate cooling power (2 kW at 70 K) for HTS (High Temperature Superconductor) power machines. The reverse-Brayton cycle with neon gas as a working fluid was adopted in the refrigerator. The prototype refrigerator does not have enough COP (Coefficient of Performance) for practical HTS applications, and the purpose of this study is to research the information required for designing a new neon refrigerator with improved performance. We take the same refrigeration cycle and working fluid as the prototype one adopted, but a lower process pressure of 1 MPa/0.5 MPa is chosen instead of 2 MPa/1 MPa. The lower process pressure is required by the turbo-compressor design and the refrigeration process is analyzed by using a newly developed process simulator. Also, a heat-exchanger configuration is studied to make the refrigerator size small. The new refrigerator will have a cooling power of 2.5 kW at 65 K, and a COP of 0.06 at 80 K..
17. T. Umeno, Keisuke Maehata, Kenji Ishibashi, Y. Kamioka, Shigeru Yoshida, K. Takasaki, K. Tanaka, Operation of a TES microcalorimeter cooled by a compact liquid-helium-free 3He-4He dilution refrigerator directly coupled to a Gifford-McMahon cooler, Cryogenics, 10.1016/j.cryogenics.2010.01.015, 50, 5, 314-319, 2010.05, A superconducting transition edge thermosensor (TES) microcalorimeter was irradiated with LX-ray photons emitted by an 241Am source maintained at an operating temperature of 120 mK using a compact liquid-helium-free 3He-4He dilution refrigerator directly coupled to a Gifford-McMahon (GM) cooler. The first and second stages of the GM cooler were directly coupled to the first and second pre-cool heat exchangers of a stick shaped dilution unit through copper plates in a vacuum chamber. The helium-free dilution refrigerator provided a cooling power of 20 μW at 100 mK. Detection signals of LX-ray photons emitted by the 241Am source were observed by operating the TES microcalorimeter in a severe noise environment induced by the mechanical vibrations of the GM cooler..
18. Masataka Iwakuma, H. Hayashi, H. Okamoto, A. Tomioka, M. Konno, T. Saito, Y. Iijima, Y. Suzuki, Shigeru Yoshida, Y. Yamada, T. Izumi, Y. Shiohara, Development of REBCO superconducting power transformers in Japan, Physica C: Superconductivity and its applications, 10.1016/j.physc.2009.05.246, 469, 15-20, 1726-1732, 2009.10, In Japan we started a national project to develop a 66/6.9 kV-20 MVA transformer with REBCO superconducting tapes in 2006. This paper gives an overview of progress of the development of superconducting transformers in Japan and also describes the fundamental technologies studied before now to realize a 66/6.9 kV-20 MVA transformer as follows. To reduce the ac loss in REBCO superconducting thin tapes, authors proposed a new method different from the conventional technique of reducing the ac loss in superconducting multifilamentary wires. It consists of scribing process into a multifilamentary structure by laser or chemical etching, and a special winding process. Making a multilayered solenoidal coil with laser-scribed REBCO tapes, we verified the ac loss reduction in proportion to a filament width even in coil configuration. In addition, to realize a current capacity more than the rated secondary current of 2.4 kA, we first investigated the workability of REBCO tapes in the actual winding process with forming a transposed parallel conductor, where REBCO tapes were bent edgewise at transposing points. Making a test coil of a 24-strand parallel conductor, we verified no degradation of the critical current and nearly uniform current distribution among the tapes. The result suggests the applicability of the method of enhancing the current capacity by forming a parallel conductor with REBCO tapes. Further, to realize the dielectric strength regulated for the Japanese standards, i.e. lightning impulse withstand level of 350 kV and excess ac voltage of 140 kV, we made test coils and carried out dielectric breakdown tests. As a result, we got hold of the required insulation distance at the important points from the viewpoint of insulation design..
19. Y. Yamanaka, T. Ito, T. Umeno, Y. Suzuki, Shigeru Yoshida, Y. Kamioka, Keisuke Maehata, Development of GM cryocooler separate type liquid-helium-free 3He-4He dilution refrigerator system, Journal of Physics: Conference Series, 10.1088/1742-6596/150/1/012055, 150, 2009.01, We developed the new liquid-helium-free dilution refrigerator system, in which the Gifford-McMahon (GM) cycle cryocooler and dilution refrigerator (DR) unit are separated. We obtained the base temperature below 50 mK in this DR system. In usual liquid-helium-free DR systems, the DR unit directly couples with GM-cryocooler in the same vacuum chamber. Therefore the mechanical vibration of GM-cryocooler is hardly removed from DR unit. In order to eliminate the vibration problem, the separated vacuum chamber contacting the GM-cryocooler is connected with the DR unit chamber by the flexible hose with length of about 1 meter. Thin flexible tubes used for circulation of the refrigerant gas and radiation shield are installed in the connection hose. The 4He gas, cooled in the GM-cryocooler unit, transfers to the DR unit throw the thin flexible tubes. After cooling the DR unit, the gas returns to GM-cryocooler unit with cooling of the radiation shield. We expect that our separate-type dilution refrigerator becomes a useful piece of apparatus for the low temperature experiments..
20. T. Umeno, Y. Kamioka, Shigeru Yoshida, Keisuke Maehata, Kenji Ishibashi, K. Takasaki, K. Tanaka, Performance of compact liquid helium free 3He-4He dilution refrigerator directly coupled with GM cooler in TES microcalorimeter operation, Journal of Physics: Conference Series, 10.1088/1742-6596/150/1/012051, 150, 2009.01, A superconducting transition edge thermosensor (TES) microcalorimeter was cooled by a compact liquid-helium-free 3He-4He dilution refrigerator with loading a Gifford-McMahon (GM) cooler for detection of LX-ray photons emitted from an 241Am source. The first and second stages of the GM cooler are directly coupled with the first and the second precool heat exchangers of a stick shaped dilution unit through copper plates in the vacuum chamber, respectively. The circulating 3He-4He gas through the precooled heat exchangers is condensed into a liquid of condense mixture by the isoenthalpic expansion through the Joule-Thomson impedance. A cascade of two mixing chambers are employed for achieving sufficient cooling power. The helium-free dilution refrigerator performs the cooling power of 20 μW at 100 mK. The TES and SQUID chips suffered from mechanical vibrations induced by a reciprocating motion of the displacer of the GM cooler. Detection signals of LX-ray photons emitted from 241Am source were observed by operating the TES microcalorimeter in severe noise environment induced by mechanical vibrations..
21. H. Sugimoto, T. Morishita, T. Tsuda, T. Takeda, H. Togawa, T. Oota, K. Ohmatsu, Shigeru Yoshida, Development and test of an axial flux type PM synchronous motor with liquid nitrogen cooled HTS armature windings, Journal of Physics: Conference Series, 10.1088/1742-6596/97/1/012203, 97, 1, 2008.02, We developed an axial gap permanent magnet type superconducting synchronous motor cooled by liquid nitrogen (LN2). The motor includes 8 poles and 6 armature windings. The armature windings are made from BSCCO wire operated at the temperature level between 66K∼70K. The design of the rated output is 400kW at 250rpm. Because HTS wires produce AC loss, there are few motors developed with a superconducting armature winding. In a large capacity motor, HTS windings need to be connected in parallel way. However, the parallel connection causes different current flowing to each HTS winding. To solve this problem, we connected a current distributor to the motor. As a result, not only the current difference can be suppressed, but also the current of each winding can be adjusted freely. The low frequency and less flux penetrating HTS wire because of current distributor contribute to low AC loss. This motor is an axial gap rotating-field one, the cooling parts are fixed. This directly leads to simple cooling system. The motor is also brushless. This paper presents the structure, the analysis of the motor and the tests..
22. Hidehiko Sugimoto, Teppei Tsuda, Takaya Morishita, Yoshinori Hondou, Toshio Takeda, Hiroyuki Togawa, Tomoya Oota, Kazuya Ohmatsu, Shigeru Yoshida, Design of an axial flux inductor type synchronous motor with the liquid nitrogen cooled field and armature HTS windings, IEEE Transactions on Applied Superconductivity, 10.1109/TASC.2007.898110, 17, 2, 1571-1574, 2007.06, A liquid nitrogen cooled axial flux type high temperature superconducting (HTS) synchronous motor was designed. This motor is an eight-pole inductor type synchronous motor with six armature windings. The field windings and armature windings are made of the BSCCO HTS wires. We called it Inductor type Flux Control Superconducting (IFCS) motor, and its output is 400 kW at the rated speed of 250 rpm. Until now, there were few armature windings using HTS wires, because of AC losses generation when the wires are used in the alternating magnetic field. In this motor, we used iron cores to decrease AC loss. Also because of the help of iron cores, it is possible to make use of armature winding at liquid nitrogen temperature. Furthermore, inductors were employed in the rotor. As a result, the cryostats that contain field HTS windings and armature HTS windings can be fixed; also we do not need the excitation devices such as the brushes and slip ring and the cooling devices such as the rotary joint to offer the path for coolant to flow..
23. Hidehiko Sugimoto, Teppei Tsuda, Takaya Morishita, Yoshinori Hondou, Toshio Takeda, Hiroyuki Togawa, Tomoya Oota, Kazuya Ohmatsu, Shigeru Yoshida, Development of an axial flux type PM synchronous motor with the liquid nitrogen cooled HTS armature windings, IEEE Transactions on Applied Superconductivity, 10.1109/TASC.2007.899959, 17, 2, 1637-1640, 2007.06, We developed an axial gap permanent magnet type high temperature superconducting synchronous motor (PMHTSSM) at liquid nitrogen temperature. There are two distinctive differences between this motor and the conventional HTS motors. The permanent magnet is applied to the field, iron cores and HTS wires are used as the armature. The motor has eight field poles, and six armature windings. The armature is put between the two fields. The field composes eight permanent magnets which are arranged as a circle. Four poles share three armature coils and there are two coils for every phase. The BSCCO wires, which are applied to armature windings, work at the temperatures of between 66 K and 70 K. The rated output is 400 kW at 250 rpm. It is known that superconducting wires have AC loss if they are operated at alternating magnetic fields. That is why there are few motors developed with superconducting armature windings. Also, there is no report of motors applying HTS wires such as BSCCO wires to armature windings. Furthermore, this motor adopted the revolving field type structure, so the brushes were not needed and the cooling system can be fixed. Also because of the axial-flux type, the structure of the cryostat can be simplified..
24. H. Kamijo, H. Hata, H. Fujimoto, A. Inoue, K. Nagashima, K. Ikeda, Masataka Iwakuma, K. Funaki, Y. Sanuki, A. Tomioka, H. Yamada, K. Uwamori, Shigeru Yoshida, Tests of superconducting traction transformer for railway rolling stock, IEEE Transactions on Applied Superconductivity, 10.1109/TASC.2007.898887, 17, 2, 1927-1930, 2007.06, We have been developing a lightweight and high-efficiency superconducting traction transformer for railway rolling stock. We designed and fabricated a prototype superconducting traction transformer of a floor-mount type for Shinkansen rolling stock. In this study, we present test results such as type test, system test and vibration test. We performed the type test in accordance with JIS, E5007. In this test, we measured the basic electrical characteristics. In the system test, we tested the transformer with a dynamic simulator for rolling stock, as a converter connected at secondary winding, and verified the operating characteristics. We performed vibration tests in accordance with JIS, E4031, vibrating the transformer on a shaking table with three-dimensional movement. As a result, we could verify that the transformer satisfied the requirement almost exactly as initially planned..
25. H. Kamijo, H. Hata, H. Fujimoto, A. Inoue, K. Nagashima, K. Ikeda, H. Yamada, Y. Sanuki, A. Tomioka, K. Uwamori, Shigeru Yoshida, Masataka Iwakuma, K. Funaki, Fabrication of superconducting traction transformer for railway rolling stock, Journal of Physics: Conference Series, 10.1088/1742-6596/43/1/205, 43, 1, 841-844, 2006.06, We designed a floor type single-phase 4 MVA superconducting traction transformer for Shinkansen rolling stock. In this study, we fabricated a prototype superconducting traction transformer based on this design. This transformer of the core-type design has a primary winding, four secondary windings and a tertiary winding. The windings are wound by Bi2223 superconducting tapes and cooled by subcooled liquid nitrogen. The core is kept at room temperature. The cryostat is made of GFRP with two holes to pass core legs through. The outer dimensions are about 1.2m × 0.7m × 1.9m excluding the compressor. Its weight is 1.71t excluding that of refrigerator and compressor. The transformer was tested according to Japanese Industrial Standards (JIS)-E5007. We confirmed that the performance of transformer has been achieved almost exactly as planned. The rated capacity is equivalent to 3.5MVA in the superconducting state..
26. Hiroshi Hata, Hiroki Kamijo, Hiroyuki Fujimoto, Ken Nagashima, Kazuya Ikeda, Masataka Iwakuma, Kazuo Funaki, Hisao Yamada, Yasutaka Sanuki, Akira Tomioka, Kenetsu Uwamori, Shigeru Yoshida, Development of a superconducting transformer for rolling stock, Quarterly Report of RTRI (Railway Technical Research Institute) (Japan), 10.2219/rtriqr.47.24, 47, 1, 24-27, 2006.02, Having undertaken studies into a lightweight and highly efficient superconducting transformer for rolling stock, we developed a prototype with a primary winding, four secondary windings and a tertiary winding using bismuth (Bi-2223) high temperature superconducting wire. Its primary voltage is 25kV, which is widely adopted as the catenary voltage on the world's high-speed lines. We adopted liquid nitrogen cooling, the weight being 1.71t excluding the refrigerator. The maximum output available to maintain superconductivity is 3.5MVA. This paper describes the transformer details and test results..
27. H. Kamijo, H. Hata, H. Fujimoto, K. Ikeda, T. Herai, K. Sakaki, H. Yamada, Y. Sanuki, Shigeru Yoshida, Y. Kamioka, Masataka Iwakuma, K. Funaki, Fabrication of inner secondary winding of high-TC superconducting traction transformer for railway rolling stock, IEEE Transactions on Applied Superconductivity, 10.1109/TASC.2005.849318, 15, 2 PART II, 1875-1878, 2005.06, We studied the possible application of high-TC superconducting traction transformer to railway rolling stock, and designed an iron core type two-leg 4 MVA superconducting traction transformer for Shinkansen. This traction transformer has a primary winding, four secondary windings and a tertiary winding. The four secondary windings are independent of each other. Two secondary windings are arranged around each leg of the iron core and placed inside and outside the primary and tertiary windings. In this study, we fabricated a high-TC superconducting coil whose form and dimension are the same as those of the inner secondary winding. This coil can be used as the inner secondary winding of the experimental high TC superconducting traction transformer that will be fabricated in the future. The inner secondary winding has 96 turns and a layer with eight parallel Bi2223 superconducting tapes. Transposition among the superconducting tapes is performed 15 times every six turns. We measured the voltage-current and AC loss characteristics when it was cooled in saturated and sub-cooled liquid nitrogen..
28. Yoshiaki Suzuki, Shigeru Yoshida, Yasuharu Kamioka, Subcooled liquid nitrogen refrigerator for HTS power systems, Cryogenics, 10.1016/S0011-2275(03)00169-3, 43, 10-11, 597-602, 2003.10, Subcooled liquid nitrogen is a good cooling medium of high temperature superconducting (HTS) electric power systems such as an electric power line and a power transformer. To produce subcooled liquid nitrogen, a cryocooler is used and a circulation pump is installed in the system. Several subcooled liquid nitrogen circulation systems were constructed and tested. Those are used as a refrigerator for HTS power systems. The pressure of subcooled liquid nitrogen is maintained at atmospheric pressure (0.108 MPa) and the working temperature is 68 K. One system of HTS power transformer was tested in distribution power line. In each case, the temperature of the cold head of the cryocooler is kept at 64 K little above nitrogen freezing temperature. For the stable operation, the system must work even in the case of shaking condition by earthquake, the pressure must be stable and be kept at atmospheric pressure..
29. Yuzo Fukuda, Kazuhiro Kajikawa, Masataka Iwakuma, Kazuo Funaki, Takaaki Bohno, Akira Tomioka, Masayuki Konno, Yujiro Yagi, Hiroshi Maruyama, Shigeru Yoshida, Katsuya Tsutsumi, Hidemi Hayashi, Kazuo Honda, Estimation of AC losses in the windings of a 1 MVA HTS transformer, Research Reports on Information Science and Electrical Engineering of Kyushu University, 8, 1, 31-36, 2003.03, AC losses in the windings of an HTS transformer are important to design its system. We fabricated an HTS transformer and measured the AC losses. We estimated the AC losses by following procedures. First, we calculated the magnetic field distribution in each turn. Secondary, we estimated the losses of each turn referring to AC losses in the strand. Finally, we can calculate the AC loss in the windings by the total sum of the losses in each turn. We compared the calculated result with observed one, and discussed the validity of the proposed method..
30. Masataka Iwakuma, Kazuo Funaki, Kazuhiro Kajikawa, Hideki Tanaka, Takaaki Bohno, Akira Tomioka, Hisao Yamada, Shinichi Nose, Masayuki Konno, Yujiro Yagi, Hiroshi Maruyama, Takenori Ogata, Shigeru Yoshida, Kouichi Ohashi, Katsuya Tsutsumi, Kazuo Honda, Ac loss properties of a 1MVA single-phase HTS power transformer, 2000 Applied Superconductivity Conference IEEE Transactions on Applied Superconductivity, 10.1109/77.920054, 11, 1 II, 1482-1485, 2001.03, We designed and built a single-phase 1 MVA-22/6.9 kV HTS transformer with the multi-layered cylindrical windings composed of Bi2223 parallel conductors. In advance of the design, the ac loss induced in the windings was estimated on the basis of the observed results in a strand. A subcooled liquid nitrogen cryogenic system with the corresponding cooling capacity was developed and attached to the transformer. The actual ac loss was measured by an electrical method. It was a great part of the total heat load and dominated the temperature rise of subcooled liquid nitrogen. We discussed the validity of the present estimation procedure of the ac loss in the windings as compared with the observed results..
31. Kazuo Funaki, Masataka Iwakuma, Kazuhiro Kajikawa, Masanori Hara, Junya Suehiro, Takehiro Ito, Yasuyuki Takata, Takaaki Bohno, Shin Ichi Nose, Masayuki Konno, Yujiro Yagi, Hiroshi Maruyama, Takenori Ogata, Shigeru Yoshida, Kouichi Ohashi, Hironobu Kimura, Katsuya Tsutsumi, Development of a 22kV/6.9kV single-phase model for a 3MVA HTS power transformer, 2000 Applied Superconductivity Conference IEEE Transactions on Applied Superconductivity, 10.1109/77.920079, 11, 1 II, 1578-1581, 2001.03, We have developed a 22kV/6.9kV HTS single-phase transformer cooled by liquid nitrogen for field test, which is a practical model for the single-phase part of a 3MVA HTS power transformer. First, we numerically simulated electromagnetic, mechanical and thermal conditions of the windings in accidental cases of short-circuit and lightning impulse, and considered the winding structure withstanding the severe loads. We constructed a small-sized model coil of Bi-2223 Ag/Mn-sheathed tapes and confirmed applicability of the design concept for the over-current and high-withstand-voltage tests. We designed and constructed a single-phase HTS transformer on the basis of the model-coil-test results. The primary and secondary windings are transposed parallel conductors of two and six Bi-2223 Ag/Mn tapes, respectively. The same tests for the HTS transformer as for usual oil-filled ones indicated the reliable operation and high performance. The field test in a distribution grid of Kyushu Electric Power Co. included inrush-current test and long-term operation of the transformer cooled by a continuous supply system of subcooled liquid nitrogen with cryocoolers..