Site:           Sumitomo Electric Industries, Ltd. (SEI)
                Osaka Research Laboratories
                1-1-3 Shimaya, Konohana-ku
                Osaka 554, Japan
                http://www.sei.co.jp/
Date Visited:   6 June 1996
WTEC Attendees: M. Suenaga (report author), 
                D. Gubser, 
                D. Larbalestier, 
                J. Willis
Hosts:          Ken-ichi Sato, Manager, 
                   Superconductivity R&D Department
                Kazuhiko Hayashi, Chief Research Associate, 
                   Superconductivity R&D Department
                Kazuya Ohmatsu, Senior Engineer, 
                   Superconductivity R&D Department

BACKGROUND

Sumitomo Electric Industries, Ltd. (SEI) is the world's second-largest producer of electrical cable, and this is its primary business. However, in recent years SEI has been diversifying its business into a number of other areas such as optical cables and specialty alloy products; currently, electrical cable sales are approximately one-half of SEI's entire business. The company is quite aggressive in R&D for new business opportunities and spends approximately 3% (~$250 million) of its sales per year on internal R&D. SEI has been working with superconductors since 1966, and it sells Nb-Ti wires for various applications. Following the discovery of high T_c superconductors, SEI researchers have aggressively pursued development of these materials for power as well as for thin film (electronic) applications (work on the films was not covered in this site visit). The SEI research team working on development of high T_c conductors is headed by Mr. Ken-ichi Sato; their contributions to the development of the Bi-2223/Ag tapes are well known throughout the world. SEI is one of the leading manufacturers of tapes, as well as of the magnets and cables that are made from the tapes.

SUPERCONDUCTING MATERIALS AND APPLICATIONS R&D

SEI's effort on superconducting materials and associated application development is carried out with ~35 researchers, of whom ~7 are devoted to development of thin film electronic applications. Another 7 work on the development of low temperature superconductors, such as Nb₃Al conductor for magnetic fusion (ITER) applications. SEI's Nb-Ti work is done in one of the business sections and is not included in the above total effort. The remaining 21 persons work on power applications of high T_c superconductors. The WTEC team was told that this effort is mainly supported by internal R&D funds, although some outside funds do come in support of these efforts, for example, from Tokyo Electric Power Company (TEPCO) for development of power transmission cables and YBCO-coated tapes; from Kansai Electric Power Company (KEPCO) for current leads and SMES coils; from Chubu Electric Power Company for terminations for superconducting power cables, and from Super-GM for development of Bi-2212 conductors. The following are highlights of SEI's accomplishments in conductor development, magnets, and large conductor applications.

Conductor Development

SEI researchers believe that the property of current Bi-2223/Ag conductors most in need of improvement is the critical current density for essentially all applications. They also believe that the key to improving J_c is in improving source powder uniformity, grain alignment, and thermomechanical processing; thus, they expend a strong effort in improving J_c in short and long tapes. Their current high values of the self-field J_c at 77 K are 42,500 A/cm² for short rolled tapes, 27,800 A/cm² for 114 m long tapes, and 17,700 A/cm² for 1,200 m tapes. They have also improved the mechanical properties of the composite tapes by additions of small amounts of Mn and Sb. In these ways they have been able to raise the critical tensile stress before the abrupt decrease in I_c from about 50 MPa to approximately 200 MPa. Another very interesting work being carried out without significant attention from the community is SEI's development of a YBa₂Cu₃O₇ coated conductor on Ni alloy tape. At present the best value of J_c at 77 K is 2x10⁵ A/cm² for a 55 cm long and ~1 µm thick tape.

The significance of this work is the fact that this impressive number is achieved without use of the ion beam assisted deposition (IBAD) technique used by most other groups working on YBa₂Cu₃O₇ coated conductors. SEI is able to achieve a textured buffer layer on a metallic substrate by controlling the temperature and angle of the substrate with respect to the direction of the plume of yttrium-stabilized zirconia (YSZ) by laser ablation. By this technique, SEI researchers are able to obtain in-plane alignment of the YSZ buffer layer as good as 12.8° (FWHM). Although not as good as that achieved by the IBAD process (~7°), it is important to note that they can deposit the YSZ at a rate of 0.5 µm/min., compared with 0.025 µm/min. in the IBAD process. Another important and possibly limiting factor for this type of conductor is its relatively low overall J_c.

The WTEC team was told that another very important area requiring attention is reduction of ac losses at power frequencies in the Bi-2223/Ag conductors. Although the team's hosts did not describe the types of research that they are carrying out toward this objective, they gave the impression they are strongly interested in this subject and are likely be putting forward a significant effort to reduce ac losses in their conductors.

Cable and Magnet Development

SEI is a leading manufacturer of large-scale model magnets and power cables utilizing multifilamentary Bi-2223/Ag tape. Table SEI.1 lists SEI's accomplishments. One of its main efforts is in the construction of power transmission cables with TEPCO, and as shown in the table, researchers have successfully produced a 7 m 66 kV/1 kA three-phase cable that operates at 1 kA_rms load-in with an ac loss of 3.5 w/m cct. They have also produced a 50 m cable conductor with a dc I_c of 2,200 A. These cables have magnetic shielding to reduce ac losses in the metallic enclosure. Although the value of the ac loss that was measured for the 7 m cable is 5-10 times greater than the value desired for commercial cables, it is impressive that SEI is able to produce a production quantity of the tape with high critical currents. SEI researchers have also provided a more than 2 km length of the tape to Fuji Electric Co. for construction of a very interesting 500 kVA power transformer in collaboration with Kyushu University.

Table SEI.1
Development of Cables and Magnets

In the area of model magnets with Bi-2223/Ag tapes, SEI is also leading the pack for the highest field, which was generated by a Bi-2223 coil. Table SEI.1 shows some of the test results. Perhaps the most ambitious attempt in the construction of a coil is SEI's plan to make a 7-10 T magnet (by the end of 1996) that is entirely wound with Bi-2223 tapes and is to be operated with a cryocooler. This will certainly consume a large amount of high quality tape and will test SEI's tape fabrication expertise and facility. It is important to recognize here that SEI is gaining crucial experience in producing high quantity tapes at commercial scale while it is constructing these devices. Also, it is interesting to hear from the WTEC team's hosts that they do not see any substantial applications of the tapes sooner than 10 to 20 years from now, and yet they are making a very extensive investment in this area.