Kengo Ohkura

Verification tests of a 66 kv HTSC cable system for practical use (first cooling tests)

Abstract Tokyo Electric Power Company and Sumitomo Electric Industries, Ltd. have been jointly developing elementary technologies for an high temperature superconducting (HTSC) cable system, such as conductor wound with HTSC wires, thermal insulation pipes, terminations and so on. Verification tests of a 100 m HTSC cable system integrating these elementary technologies have been conducted in collaboration with Central Research Institute of Electric Power Industry (CRIEPI) to verify its long term electric and cryogenic properties. The cable conductor is composed of four layers of Bi-2223 wires wound spirally around a former. Polypropylene laminated paper impregnated with liquid nitrogen is adopted as cable insulation for its properties of high insulation strength and low dielectric loss. HTSC wires are also wound around the electrical insulation to form an electrical and magnetic shield. To reduce heat invasion from ambient temperature part, multi-layer insulation is wound between the co-axial stainless corrugated pipes where high vacuum is maintained. The cable was partially installed into a ∅ 150 mm duct and formed in a U-shape. Each end has a splitter box and three terminations. The cable and the terminations are cooled using two separate sets of a pressurized and sub-cooled liquid nitrogen cooling system. The cable has been developed and laid at CRIEPIs test site and long-term tests have been under way since June, 2001. This paper presents the design of the cable and some results of the first cooling tests.

High field generation using silver-sheathed BSCCO conductor

Abstract A J c (77 K) of a 1200 m long silver-sheathed bismuth-based superconducting wire has reached 10 900 A/cm 2 . The performance of application prototypes has also got a great deal of progress. For example, a 60 mm bore BSCCO magnet generated 4 T at 4.2 K, 3 T at 21 K, and stably generated 2.5 T at 21 K for over 150 h when cooled with GM refrigerator. This magnet has a practical-sized winding bore of 60 mm, and a 40 mm RT bore cryostat was installed for actual application. Also. high magnetic field properties of another BSCCO magnet having a 40 mm winding bore were evaluated with a backup field up to 22.54 T at 4.2 and 27 K. The maximum fields generated by a backup hybrid magnet and BSCCO coil was 24.0 and 23.4 T at 4.2 and 27 K, respectively.

Generation of 24.0 T at 4.2 K and 23.4 T at 27 K with a high‐temperature superconductor coil in a 22.54 T background field

The 4.2 K and 27 K current‐carrying performance of a high‐temperature superconducting (HTS) coil was measured in background fields up to 22.54 T generated by a hybrid magnet (Hybrid III) at the MIT Francis Bitter National Magnet Laboratory. The coil, 40 mm winding i.d., 108 mm winding o.d., and 113 mm high, consists of 17 double pancakes, each wound with silver‐sheathed BSCCO‐2223 tapes. Each pancake is the product of a react‐and‐wind method. In total, the test coil contains ∼1200 m of BSCCO‐2223 conductor weighing ∼7 kg. Prior to the measurements in Hybrid III, the coil was tested in zero background field in the temperature range from 4.2 to 77 K. It was coupled to a Gifford–McMahon type cryocooler and at 15 K generated a peak field of 2.1 T; at 18 K, it generated 1.9 T, operating continuously for ∼50 h. In a 22.54 T background field of Hybrid III, the coil reached critical currents of 116.5 A ([Jc]sc, critical current density based on the BSCCO cross‐sectional area only, of 261 A/mm) at 4.2 K and 67 A (...

DI-BSCCO wires by Controlled over pressure sintering

Sumitomo Electric successfully developed drastically innovative Bi-2223 (DIBSCCO), namely, commercially produced Bi2223 long length wires using the controlled over pressure sintering (CT-OP) with unique properties quite different from conventional silver sheathed BSCCO wires. CT-OP prevented pores occurring in BSCCO cores, so it reformed conventional Bi2223 wires to DI-BSCCO with excellent properties of higher critical currents, stronger mechanical strength and better durability against temperature rise in cryogen such as pressurized liquid nitrogen. It enhanced the critical current by 50 percent conventional wires sintered in normal atmospheres. Critical tensile stress was also improved by more than 150 percent. Any ballooning defects and degradation of critical current, one of the critical problems for the conventional BSCCO wires, were not found in full length of several km long DI-BSCCO tapes after 24 hours immersion into 1MPa liquid nitrogen.

Development of a 100 m, 3-core 114 MVA HTSC cable system

Abstract We have started a project to develop a 100 m 3-core 66 kV/1 kA/114 MVA high temperature superconducting (HTSC) cable system to certify the manufacturing capability and the practicability of an HTSC cable system for use as actual power system equipment. The cable is designed based on the results of a 30 m, 3-core test cable. The cable is composed of a conductor and a shield wound with Ag–Mn sheathed Bi-2223 tapes, electrical insulation with polypropylene laminated paper impregnated with liquid nitrogen and thermal insulation with co-axial corrugated pipes. The three cores are housed in this thermally insulated pipe. The cable has been developed and laid at CRIEPIs test site and long-term tests have been under way since June.

Development of High-Tc Superconducting Magnet Using Ag-Sheathed Bi2223 Tapes

We have succeeded in developing two types of the refrigerator cooled High-Tc superconducting magnets; 4-Tesla and 7-Tesla types. They have the same inner diameter of 80 mm and outer diameter of 292 mm, but the coil height was increased to 200 mm of 7-Tesla type from 68 mm of 4-Tesla type. The 4-Tesla type successfiilly produced the central magnetic field of 4.0 Tesla over 30 minutes and 3.5 Tesla for 48 hours. High ramp rate excitation up to 0.35 Tesla per second was achieved, which was a hundred times faster than that of the refrigerator-cooled magnets using the metallic superconductors. The 7-Tesla type magnet stably generated 7.1 Tesla over 24 hours and was excited at a rate of 2 Tesla per minute.

Performance of all high-Tc superconducting magnets generating 4 T and 7 T at 20 K

Refrigerator-cooled all high-Tc superconducting magnets, i.e. coils and current leads, 4 T and 7 T types, have been developed. The 4 T type successfully produced a central magnetic field of 4.0 T over 30 min and 3.5 T for 48 h. High ramp rate excitation up to 0.35 T s-1 was achieved. The 7 T type magnet stably generated 7.1 T over 24 h and was excited at a rate of 7 T min-1 . These ramp rates were 20-100 times faster than that of the refrigerator-cooled magnets using metallic superconductors. A new cooling scheme and stability criterion for conduction-cooled magnets are proposed.

Controlled Overpressure Processed Bi2223 Wires for Power Applications

Progress in the performance of the controlled overpressure (CT‐OP) processed (Bi,Pb)2Sr2Ca2Cu3Ox (Bi2223) wire is reviewed. Optimization of the CT‐OP processing improved microstructure of Bi2223 wires and increased their critical current (Ic) by greater than 60% compared to normal pressure processing. The CT‐OP processing effectively removed pores and cracks. The SEM show CT‐OP wires had very dense, uniform, and well connected Bi2223 grain. Densification of the CT‐OP wires prevents liquid nitrogen penetration during long term exposure to liquid nitrogen of them for use in power cable applications. Ballooning caused by trapped nitrogen, that expands when warming up to room temperature, doesn’t occur in CT‐OP wires. These high performance levels in CT‐OP wires have enabled commercial level applications such as power cables, magnets and motors.

Recent progress of HTS magnet using Bi-2223 Ag-sheathed wire

The authors have succeeded in developing two types of refrigerator cooled high-Tc superconducting magnets-a high magnetic field type and a large bore type. The high magnetic field type has a room temperature bore of 50 mm, an inner diameter of 80 mm and an outer diameter of 300 mm. The coil height is 200 mm, using 24 double pancakes. The magnet generated 7.1 T over 24 hours and was excited at a rate of 7 T/minute. This high ramp rate was ten times faster than that of a refrigerator cooled magnet using metallic superconducting wires. The large bore type magnet has a room temperature bore of 280 mm, an inner diameter of 400 mm and an outer diameter of 520 mm. The coil height is 18 mm using 2 double pancakes. The magnet generated 0.17 T and was excited at a rate of 0.034 T/s. These two types of HTS magnets, produced by using only Bi-2223 Ag-sheathed tapes, have been continuously operated at 20 K for practical applications.

Development of Ag-sheathed Bi2223 superconducting wires and their application to magnets

Silver-sheathed BiPbSrCaCuO 2223 superconducting wires with long length and high Jc of over 10/sup 4/ A/cm/sup 2/ were developed by using the powder-in-tube method. Future possibilities to obtain much higher Jcs are discussed in relation to crystal alignment, connectivity between grains and flux pinning. High amperage wires and high strength wires were also developed for large scale magnet application. High I/sub c/ of over 300 A at 77 K were obtained for the wire with large cross sectional area. Good stress and strain tolerant characteristics were also obtained for silver alloy sheathed wires. In order to apply the HTS wires for AC use, it is necessary to reduce AC loss. So, the AC loss of the wires are also discussed. As a progress of wire technology, we have fabricated many types of magnets, such as pancake magnets and solenoidal magnets. In the case of 77 K application, it is promising to apply for AC use because of large heat capacity of HTS wires and liquid nitrogen. So, we are developing the 500 kVA transformer and pulse magnet for SMES. A refrigerator cooled magnet operated near 20K was fabricated. This magnet was operated at 21 K and generated 3 T inside a /spl phi/40 mm room temperature bore, stably generated 2.5 T continuously for over 150 hours and could be operated at high ramp rate of over 12 T/min. As for the 4.2 K operation, high field insert magnet for 1 GHz NMR application are developed. Highest magnetic field of 24 T was achieved using the hybrid magnet at MIT and persistent current mode operation was done by using the layer wound coil with persistent current switch.