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Site: Toshiba Corporation
Toshiba Heavy Apparatus Laboratory (Keihin Operation)
2-4 Suehiro-cho, Tsurumi-ku
Yokohama, Japan
http://www.toshiba.co.jp/index.htm
Date Visited: 5 June 1996
WTEC Attendees: M. Suenaga (report author),
D. Gubser,
D. Larbalestier,
J. Willis
Hosts: Dr. Masami Urata, Deputy Manager,
Superconducting Technology Group,
New Energy Technology Department
Mr. Susumu Mine, Chief Specialist,
Advanced Research Devices Staff,
Machine and Equipment Department
Dr. Yutaka Yamada, Senior Research Scientist,
Research Laboratory,
Energy and Mechanical Research Laboratories,
Toshiba Research and Development Center
Mr. Yoshihiro Waichi, Group Manager,
Electromagnetic Engineering Department,
Superconducting Magnet Group
Toshiba Corporation is one of Japan's largest manufacturing companies. Its business covers a wide range of products, from home appliances and semiconductors to large electric power equipment. The WTEC team visited Toshiba Heavy Apparatus Laboratory (Keihin Operation) in Yokohama, where Toshiba manufactures its large electric equipment (electrical generators, large motors, etc.). All of its large superconducting apparatus is also constructed at this site, after extensive R&D of the particular system is performed at the Toshiba Research and Development Center at another site. Toshiba has been interested in applications of superconductivity for many years and has manufactured a number of high field magnets and other superconducting systems. Some currently active applications were discussed at the site visit, and these as well as Toshiba's outlook on applications of high Tc superconductors are summarized briefly below.
At Keihin Operation, there are four main projects, all currently at the manufacturing stage:
All of these magnets employ low Tc superconducting components, except for the current leads for the fault-current limiter and the cryogen-free magnet. Toshiba also manufactures magnets for magnetically levitated trains, but these are constructed at its Fuchu Works, where the primary business is transportation products. The Keihin Operation also produces large magnets for single crystal growth of semiconductors and for MRI. Before discussing the technical aspects of these main activities, it is important to note that the WTEC team came away with the strong impression that as a result of the construction of many types of devices over the years, the Keihin Operation of Toshiba maintains a tremendous knowledge and expertise in the manufacturing technology of superconducting and cryogenic devices. Most of these construction activities probably are supported by one type or another of national or power company project, even though Toshiba also puts in a substantial amount of its own R&D funds.
As a part of the Super-GM project, Toshiba has been actively engaged in research and development of the superconducting generator. (See the Super-GM site report about the scope of this project.) Toshiba's part of the project is to study a quick-response-type rotor, and it has constructed a half-length rotor to be tested in-house. The objective of this study is to design, construct, and verify the design of a superconducting rotor that can respond quickly enough to external electrical disturbances to provide electrical system stability. In constructing this rotor, Toshiba had to develop a new type of Nb-Ti wire with Furukawa Electric Cables, Ltd., in order to minimize ac losses due to a sudden large change of magnetic field (3.8 T/sec). It has conducted in-house a number of tests to verify the suitability of the rotor for the quick-response-type generator. At the time of the WTEC visit, it was constructing a full-sized model rotor for the 70 MVA generator, to be tested in 1998 at Super-GM's Kansai site. During the tour of the factory, the WTEC team was shown at a distance the half-length unit, and it was quite an impressive sight.
This is a part of MITI's SMES program managed by ISTEC, and the WTEC team did not find out many details about this project. However, as an initial step in studying a 100 kWh 20 MVA SMES pilot plant, Toshiba has constructed a large coil (~3.5 m in OD and 0.23 m in thickness), which is being tested at JAERI and was to be sent in 1997 to Lawrence Livermore National Laboratory in the United States for further tests. This R&D coil has the same diameter but only one-half the thickness of the unit required for the pilot plant. The complete system requires 12 full-size units. One interesting feature of the coil is its use of cable-in-conduit Ni-Ti conductors for very high currents (20 kA). The cable contains Nb-Ti wires designed for low ac loss that incorporate CuNi matrix and oxidized strand surfaces to reduce interstrand coupling. The panel's hosts did not discuss the program beyond the testing of the coil.
This is a project that is carried out in collaboration with Tokyo Electric Power Co. that has been going on since about 1990. At the time of the WTEC team's visit, Toshiba had recently constructed a 6.6 MVA (6,600 V/1,000 A) single-phase unit. The unique feature of this unit was that it was a closed system, i.e., it did not require replenishment of liquid helium because it incorporated a 4.2 K refrigerator in the unit. It also employed high-stability and low-ac-loss Nb-Ti wire as well as high Tc superconducting current leads, which helped to reduce the size of the unit. The next stage of the current limiter project, as the team was told, is to focus on improvement of the insulation so that the voltage can be raised to the 500 kV level. Toshiba engineers are planning to accomplish this by 2010.
One of the very popular activities in the area of superconducting applications in Japan is construction of cryocooled high magnetic field magnets. With widespread availability of high Tc superconducting current leads, it has become possible to construct superconducting magnets that will run without the use of liquid helium. Because liquid helium is very expensive in Japan, the idea of having a superconducting magnet that can be turned on without the need for liquid helium has became very attractive, and a number of manufacturers have produced these magnets for sale. Toshiba is one of the first to commercialize a couple of models, a 5 T magnet with a 300 mm warm bore and a 10 T magnet with a 100 mm warm bore. The 10 T unit is particularly impressive. To achieve this, Toshiba incorporates a special 4 K cryocooler that was developed at the Toshiba Research and Development Center and is now being manufactured by a subsidiary.
The high Tc materials program at Toshiba is carried out at the Toshiba Research and Development Center with approximately ten staff members. This effort is primarily focused on fabrication of Bi-2223/Ag tapes and current leads and is lead by Dr. Y. Yamada. One of his recognized accomplishments is the fabrication of Bi-2223/Ag tapes with the highest reported critical current density achieved at the time of 6.6 x 104 A/cm2. In the process of making the high Jc tapes, he has pointed out the importance of the green powder density in the tape throughout the mechanical deformation process in order to achieve high current density tapes. More recently, his group has successfully incorporated Mg in the Ag matrix to improve the tape's mechanical strength to 120 MPa. It also fabricates the current leads for incorporation into Toshiba's devices such as the current limiter and the cryogen-free magnets when these are being studied. However, it was not clear to the panel whether or not Toshiba's commercial units contain Toshiba's own current leads.
It appears that the Toshiba R&D Center staff are interested in the investigation of high Tc materials only to the extent that they have knowledge of the processes and the limits of each material, for possible future product applications. They believe that knowledge of the conductors may be important for construction of some devices in the future. Toshiba's relatively small interest in this subject is due to the fact that the company is not a prime manufacturer of wires and cables. In the past, its researchers have also studied and developed low Tc wires as R&D projects, and some of the results from the studies were incorporated in production of the wires by Showa Electric Cables, Ltd., with which Toshiba works quite closely from time to time. A similar scenario is also possible with high Tc materials, as Showa is fabricating both Bi-2212 and Bi-2223/Ag tapes.