ELECTRIC WIRE & CABLE, ENERGY

Examples and Future Prospects of High-Temperature Superconductor Products

Yuichi YAMADA, Masaharu MOGI and Ken-ichi SATO

It has been 20 years since the discovery of high-temperature superconductor (HTS), and Bi2Sr2Ca2Cu3O (BSCCO) is still the only commercial-level HTS wire. By using the “Controlled Over Pressure (CT-OP)” process, Sumitomo Electric Industries has developed not only the world’s longest HTS wires but also special HTS wires such as those for AC use. Sumitomo Electric’s DI-BSCCO HTS wires has been successfully used in various HTS applications including power cables, ship propulsion motors, maglev trains, railroad transformers and high-field magnets. The commercialization of HTS technology will be accelerated as the performance and cost- effectiveness of HTS wire are improved. The HTS market is expected to be boosted in the second decade of the 21st century.

1. Introduction reason YBCO wire discovered before BSCCO wire is called 2G wire is to raise expectations. Compared with In the field of superconductors, bismuth supercon- BSCCO wire, YBCO wire has good critical current (Ic) ducting wire is called first generation (1G) supercon- versus magnetic field (B) characteristics and low pro- ducting wire and yttrium superconducting wire is called duction cost, because smaller silver amount is required second generation (2G) superconducting wire. This in making a wire. Although the material cost for YBCO may cause some people to think that 2G wire is newer wire is less than that for BSCCO wire, the production and more advanced than 1G wire, but looking back at process of YBCO wire is more complex and has not the history of the development of superconductors been optimized yet. Therefore, YBCO wire is more proves that it is not true. expensive than BSCCO wire. Reducing the production As a matter of fact, yttrium-based 2G superconduc- cost for YBCO wire to be below that for BSCCO wire is tor Y1Ba2Cu3O7 was discovered in the United States in possible, but many breakthroughs need to be made first. 1987 and it is the first superconductor whose critical In fact, Tc and the critical magnetic field (Hc2) of temperature (Tc) of 90 K is higher than the boiling BSCCO are much higher than those of YBCO, and there point of (77K, -196˚C). The reason why is a good chance that there are breakthroughs in this type of superconductor is called the “high-tempera- BSCCO. Also, because YBCO wire has more variations in ture superconductor” is that its Tc is higher than the materials and production processes than BSCCO wire, temperature speculated from the BCS theory. In 1988, many research institutes own many intellectual proper- the next year of the discovery of Y1Ba2Cu3O7, a new ties, presenting a serious obstacle to commercialization. superconducting material was discovered in Japan. It is On the other hand, the development and commer- Bi2Sr2Ca2Cu3O10 and this superconductor had set the cialization of BSCCO wire are conducted by only a few new record of Tc = 110 K, which is 20 K higher than that companies in the world, one of which is Sumitomo of the one discovered previous year. It would have been Electric Industries, Ltd. Nowadays, reasonably priced appropriate if Bi2Sr2Ca2Cu3O10 had been called the “sec- BSCCO wires are commercially available, and trial pro- ond generation” (or next generation) superconductor, duction of superconducting equipment using such but it is not called so. Instead, Y1Ba2Cu3O7, which is hard BSCCO wires is underway. It is expected that even if to be made into long wires, is called 2G. After the dis- YBCO wire is offered commercially as the best supercon- covery of Bi2Sr2Ca2Cu3O10, the development of long ducting wire in the future, the market for superconduct- superconducting wire had been promoted and the trial ing products is incredibly large and can be still exploit- production of such applied products as power leads, ed. Therefore, it is important that superconducting superconducting magnets, superconducting transform- products using BSCCO wire are developed now. ers and power cables had started. It was very difficult to Fortunately, trial-developed YBCO wire is similar in produce long-length Bi2Sr2Ca2Cu3O10 wire exceeding dimensions to BSCCO wire that is now a de-facto stan- 1000 m that has a high critical current at low cost, so dard for superconducting wires, so it will be easy to there are opinions that it may be difficult to break thor- switch from BSCCO wire to YBCO wire. The authors ough the technical limit of Bi2Sr2Ca2Cu3O10. Therefore, expect that in the future YBCO will not drive BSCCO it is harder to receive governmental support for out of the market, but each brings out its own character- researches on Bi2Sr2Ca2Cu3O10. Many researchers who istics and coexist in the market. want to receive governmental funds shifted their research focus from Bi2Sr2Ca2Cu3O10 (BSCCO) to Y1Ba2Cu3O7 (YBCO). There are speculations that the

SEI TECHNICAL REVIEW · NUMBER 65 · OCTOBER 2007 · 51 2. BSCCO wire blocking layers that can be easily cleaved. The CuO2 planes in polycrystalline bismuth cuprate can be easily 2-1 Types of BSCCO aligned when formed into a tape using the powder-in- There are three types of bismuth-based supercon- tube process including rolling and sintering, thanks to (1) ducting materials: Bi2Sr2Cu2O6 (Tc = around 25 K ), this cleavage easiness. (2) Bi2Sr2CaCu2O8 (Tc = around 80 K ) and Bi2Sr2Ca2Cu3O10 (Tc = around 110 K, Fig. 1). They are named Bi2201, Bi2212 and Bi2223, respectively, after the constituent ele- Powder Wire formation Sintering ment ratio. In the early stage of development, Bi2212 was Calcination FillingDrawing Assembling Drawing 1st rolling easier to synthesize than Bi2223 and Bi2212 wires had 1st sintering higher critical currents than Bi2223 wires at low tempera- tures around liquid helium temperature. However, Repeat because Bi2212 wires cannot be used at liquid nitrogen 2nd rolling 2nd sintering Silver tube Silver tube temperature and also due to the recent improvement of Milling for single rod for outer sheath Bi2223 wires and the progress of applications utilizing them, the most common type of bismuth wire today is Fig. 2. Bismuth high-temperature superconducting wire manufactur- Bi2223 wires. ing process

2-3 Production and marketing of Bi2223 wires BiO Bi2223 wire generally has a shape as shown in Fig. 3 SrO with a thickness a little over 0.2 mm and a width a little CuO over 4 mm. The critical current (Ic) is generally defined Ca CuO as the current at which 1 micro-volt per centimeter will Ca be generated under a 1 atm atmosphere and self field. CuO The Ic value of commercial BSCCO wire is around 90- SrO 150 A, but Sumitomo Electric reported in a published BiO paper that its BSCCO wire had set a world record with Ic of 210 A. Nowadays, BSCCO wire is the only high-tem- perature superconducting wire that can be mass-pro- duced into long wires over 1000 m in length.

4.0 - 4.5mm

0.2~ 0.25mm Fig. 1. Bi2223

Ag Superconducting filament 2-2 Fabrication process of Bi2223 wire The crystal structure of Bi2223 has sheet-like two- Fig. 3. The cross-sectional view showing a frame format of Bi2223 superconducting wire with multi-filaments structure. dimensional CuO2 square lattices at which superconduc- The black regions are superconducting filaments. tivity occurs. The CuO2 planes have electricity-insulating blocking layers above and below them, forming a layer structure of CuO2 planes and blocking layers superim- In order to align crystals and increase critical cur- posed on each other. This particular structure results in rent value, a tape shape is adopted. Even if the wire has anisotropic transport property, which allows the current a tape shape, superconducting cuprate is ceramic and to flow along the CuO2 planes while suppressing the therefore is brittle. The electric conductor of BSCCO current from straddling the blocking layers. Due to this wire has a multi-filamentary structure that consists of property, the achievement of high critical currents ribbon-like filaments embedded in a silver matrix, there- depends on the alignment of the CuO2 planes along the fore it undergoes little degradation when bent. current path in the wire. Because cuprate superconduc- In the case of NbTi or Nb3Sn superconducting wire, tors are brittle ceramics, unlike ductile materials like it is impossible to conduct the critical current test along cupper, aluminum and superconducting Nb-Ti alloy, the entire length because the test needs to be per- they cannot be formed into wires by the deformation formed in liquid helium. However, in the case of high- process. Therefore, cuprate superconducting wires are temperature superconductor, quality can be assured made by a method called either “powder-in-tube” or “sil- over the entire wire length by measuring the critical cur- ver sheath”, which consists of filling the raw material rent for the entire wire length in liquid nitrogen. powder into a silver tube, deforming it into a wire and 2-4 DI-BSCCO (3) sintering it into a polycrystalline superconductor (Fig. BSCCO wire, which became the first practical high- 2). Bismuth cuprate has weakly bonded areas in its temperature superconducting wire, had a intrinsic prob-

52 · Examples and Future Prospects of High-Temperature Superconductor Products lem. Ceramic superconductor had pores through which indicates that much residual Bi2212 and Pb-rich phases liquid nitrogen penetrates, so when a wire was quickly exist in the Bi2223 superconductor. Since supercon- warmed after liquid nitrogen cooling, liquid nitrogen ducting current path is limited in non-superconducting inside the superconductor was gasified and caused a phases, it is expected that the reduction of these phases wire defect called “ballooning”. Some manufacturers further increases the Ic values. decided to enclose the wire in a metal sheath so that 2-5 BSCCO wire for AC applications (4) wire strength is improved, but Je (the critical current Although a superconductor is free from energy dis- density for the entire wire cross-section) decreased. sipation under a direct current, the magnetic hysteresis On the other hand, because the pores act as an in the superconductor causes an energy loss called “AC obstacle to the improvement of critical current, some loss” with an alternative current. An effective method to manufactures and institutes considered implementing a reduce AC loss is to make the hysteresis loops smaller by fundamental solution to this problem, which is to apply breaking up the superconductor into small pieces. pressure during heat treatment, but advanced technolo- However, this structure is not sufficient enough because gy was needed to realize such a technique. Sumitomo the filaments behave as if they were a single supercon- Electric developed a special pressurized sintering tech- ducting bulk due to a coupling current induced by elec- nology called CT-OP (stands for “controlled over-pres- tromagnetic induction. To suppress the coupling cur- sure”), and established a mass-production facility for rent, the wire is twisted so that the filaments become spi- BSCCO wire. The company not only used this CT-OP ral around the center axis of the wire and the high-resis- technology but also improved the entire BSCCO wire tance barrier layers are arranged between the filaments production process from material composition to final (5). This structure is also used in low-temperature super- sintering. Sumitomo Electric’s BSCCO wire is marketed conductors like NbTi. under the brand name DI-BSCCO, which means In general, a temperature rise occurs more easily at “dynamically-innovative BSCCO”. low temperatures because specific heat is smaller in low Using this new sintering process, the density of temperatures. In a superconducting device that carries a superconducting filaments was improved to almost large current, Joule heat is generated when the super- 100% from around 85% of conventional sintering conducting state deteriorates as a result of temperature processes. As a result, the critical current and mechani- rise. This causes a phenomenon of steep temperature cal properties are improved. This type of heat treatment rise called “quench”. The quench phenomenon is ham- process is generally called “hot isostatic pressing (HIP)”, pering the practical use of low-temperature supercon- and the process is usually performed in an inert gas ductor in AC applications despite many years of atmosphere to prevent the oxidation of heat-treatment research. chamber, but BSCCO wire needs oxygen in the sinter- The specific heat of a substance like increas- ing process and therefore special steel needs to be used. es by a hundredfold at 20 K and by a thousandfold at 77 It is also necessary to control the oxygen partial pressure K compared to that at 4 K. This means that temperature exhaustively and to control the temperature over 800 rise is greater at higher temperatures. Moreover, refrig- degrees C at an accuracy higher than that obtained by eration efficiency is better in higher temperature commercially-available thermo couples. regions. In addition, because the allowable temperature The CT-OP process not only eliminates “balloon- rise limit of high-temperature superconductor is high ing” but also increases the critical current and mechani- due to the large difference between the operating and cal properties of DI-BSCCO. It is confirmed that DI- critical temperatures, high-temperature superconductor BSCCO recently achieved a critical current over 210 A can work stably in AC operations where heat is generat- and/or a unit length over 2000 m. However, a detailed ed constantly, . observation of CT-OP-sintered superconducting wire It was already confirmed that a novel superconduct- ing tape fabricated by modifying a conventional 110-A DC tape to have a narrower size and twists has a low AC loss between one-third and one-fifth those of conven- tional DC-use tapes. A dramatic progress can be achieved in superconductor for AC use if a low AC loss tape with a critical current around 100 A is developed using the technologies for 200 A tapes.

3. Applications of superconducting wire

3-1 Features and applications of superconductor There are four basic features of : (1) Perfect zero resistance (perfect conductivity), (2) perfect diamagnetism, (3) flux quantization, and (4) Josephson effect. The examples of possible applications Photo 1. DI-BSCCO of superconductivity are shown in Fig. 4.

SEI TECHNICAL REVIEW · NUMBER 65 · OCTOBER 2007 · 53 From the view point of application to electric power superconducting cables can transmit large amounts of transmission/distribution, zero resistance and high cur- electricity, construction costs can be reduced and trans- rent density are the two important characteristics. mission losses are low, meaning that superconducting Because the resistance is zero, compact conductors that cables are economical. They can be used to supply low- feature low transmission loss and high voltage, large-current power, and because the charging can be achieved. The zero resistance characteristic also current has little influence, long-distance power trans- allows the realization of compact high-field magnets mission can be achieved. As a result, the use of super- that provide low heat generation and high current den- conducting technology allows the elimination and sim- sity. The applications shown in Fig. 4 (other than elec- plification of intermediate substations and switching sta- tronic-related applications) are the uses of conductors tions in urban suburbs. or high-field magnets. Superconducting cables also has environmental The applications of the Josephson effect include advantages. They are EMI-free (superconducting shield devices such as voltage standards, high-speed switching layer prevents electromagnetic wave leakage), energy elements and superconducting quantum interference saving (low power transmission loss) and non-flammable devices (SQUIDs) used for micro-magnetic field sensors, (does not use oil that is used in oil-insulated cable). but this paper only discusses the applications of conduc- R&D on superconducting cables is conducted all tors and magnetic fields. over the world. After the success of three superconduct- ing cable projects (the Tokyo Electric Power Company Project, the Copenhagen Project and the Southwire Catapult Project) in around 2000, many demonstration projects were implemented mainly in the United States and Asia. Generator Particle accelerator Nuclear fusion reactor Table 1 shows the superconducting cable projects Fault current limiter Ship Chemical reaction Crystal pulling apparatus around the world. Energy storage Magnetic separation SQUID SR Table 1. Superconducting cable projects around the world Mobile phone base station Super computer MRI Project Member Utility FundBudget Cable Type End Wire Period Etc. Maglev train 3-in- TEPCO SEI TEPCO Private 18M$ AC66kV- CD Fiexd Bi2223 SEI 2001-2002 Transformer 1000A-100m One Power cable Danish Single Copenhagen NKT AC30kV- WD Bi2223 NST 2001-2003 Automobile motor DOE 2000A-30m × 3 Single Southwire Southwire DOE AC12.5kV- CD Bi2223 IGC 2000- 1250A-30m × 3 Fig. 4. Superconductor Applications Single Detroit Pirelli Detroit DOE AC24kV- WD Bi2223 AMSC 2001.10- Failed Edison 2400A-120m × 3 Super-GM No Super- METI/ AC77kV- Single (Furukawa, CD × Bi2223 — 2004-2005 Heat ACE CEPRI) NEDO 1000A-500m 1 Cycle 3-2 Superconducting power cable China (6) (1)Superconducting power cable Innopower, Yunnan S&T, InnoST, Beijing AC35kV- Single Inno Yunnan Electric 4.3M$ WD × Bi2223 2004.4- Superconducting power cables have many advan- Shanghai City, 2000A-33.5m 3 ST Cable Power Yunnan tages, which are shown in Fig. 5. Since compact-size Prov. LS cable, Korean AC22.9kV- 3-in- 2004.5-12 DAPAS KEPRI, KEPCO MOST CD One Bi2223 AMSC KIMM 1250A-30m IEE/CAS, Economical Advantages Environmental Advantages Cahngtong China AC10.5kV- Single La´nzho¯u 1.2M$ WD Bi2223 AMSC 2005- Economic Efficiency Power Cable S&T 1500A-75m × 3 (Cost/Capability) Company Large Power Transmission Capability KEPRI, SEI, KEPCO, Environmental- AC22.9kV- 3-in- Low Power Transmission Loss KEPRI KERI, KBSI, KEPCO Korea 2.3M$ CD Fiexd Bi2223 SEI 2006- Alive Reduction of friendliness etc. Gov. 1250A-100m One Operating Costs (Reduction of CO2 Emissions) KEPRI LS cable AC22.9kV- CD 3-in- Bi2223 AMSC 2007- 1250A-100m One Existing Conduit Effective Use of (Replacement/Addition) Existing Facilities SuperPower, National DOE, 3-in- Bi2223 SEI On Compact Size Albany 26M$ AC34.5kV- CD Fiexd 2006- SEI, BOC Grid NYSERDA 800A-350m One (YBCO*) (SP*) Grid Substation American (Elimination/Simplification) On Ohio Ultera, Electric DOE AC13.2kV- CD Triaxial Bi2223 AMSC 2006- Low Voltage & Large Current ORNL 9M$ 3000A-200m Grid Low Charging Power Current Long (Long Distance Power AMSC, under LIPA 1 Nexans, Island DOE AC138kV- CD Single Bi2223 AMSC 2007 construc- Transmission) Power 46.9M$ 2400A-660m × 3 AirLiquide Authority tion. EMI-Free Environmental- friendliness METI/ 3-in- On Grid SEI TEPCO AC66kV- CD Fiexd Bi2223 SEI 2007-2011 started Disaster Prevention NEDO 22.5M$ 200MVA-300m One Non-explosive/Non-flammable No Industrial (Safety) AMSC, Con- Waste Hydra DHS 39.3M$ AC13.8kV CD Triaxial Bi2223 AMSC 2007-2011 started Non-hazardous (Nitrogen Gas) (toward Recycling- Southwire Edison oriented Society) AC13.8kV- Southwire, 2007-2010 Long Service Life (High Reliability) Entergy NKT Entergy DOE 26.6M$ 60MVA- CD Triaxial TBD TBD planning (Low Temperature Use, Small 1,760m Advantages in Temperature Variations during AMSC, Nexans, AC138kV- Single Operation) Terms of Service LIPA 2A LIPA DOE 18M$ CD × YBCO AMSC 2007-2013 planning Life/Reliability AirLiquide 2.4kA 3 AC50kV- KNT, 2008-2011 Amsterdam Plaxair Nuon TBD TBD 250MVA- CD Triaxial TBD TBD planning Fig. 5. Features and advantages of superconducting cable 6,000m

54 · Examples and Future Prospects of High-Temperature Superconductor Products (2) Albany Project (7) world’s first HTS cable-to-cable joint was placed inside a In the United States, the aging and vulnerable vault, and both ends of the cable were connected to transmission grid is acknowledged as the cause for the overhead power transmission lines. Photo 2 shows the Northeast Blackout of August 2003 and the upgrading cable structure and Table 2 shows the cable parameters. of the grid calls for urgent attention. In the Energy The cable system was connected to the actual power Policy Act enacted in August 2005, the upgrading of the grid of National Grid at 21:00 on July 20, 2006 local time. transmission grid is defined as an urgent issue of nation- About 7,000 hours (10 months) have passed since the al importance. As one of the initiatives, the “Grid 2030” cable system was connected to the grid, and the system program for constructing a powerful superconducting transmits power to Albany without any trouble. One time electricity grid by 2030 is now being considered. For this the cable experienced a fault current and the breaker purpose, three superconducting cable projects funded functioned normally, which caused the operation to sus- by the United States Department of Energy are current- pend. The cable was deliberately checked, but no dam- ly under way. The first project implemented was the age on the cable or the system was found and the opera- Albany Project in which Sumitomo Electric participates. tion was resumed. In the summer of 2007 the world’s In the project, superconducting cable was connected to first demonstration of the superconducting cable the real power grid. replacement was implemented and is going on. The 350- The project is implemented on an actual power grid m cable was disconnected at the cable joint to replace extending approximately 3 kilometers between two sub- the 30 m portion with a new superconducting cable. stations (Menands and Riverside) of the power company (3) KEPCO Project National Grid (formerly Niagara Mohawk) in the city of As a case study on the practical application of super- Albany, the capital of New York State. In the project, a conducting technology, the Korea Electric Power superconducting cable was applied to a 350-meter sec- Corporation (KEPCO) is planning to conduct researches tion across a freeway. The nominal voltage, current and on the procedure for practical operation of supercon- capacity are 34.5 kV, 800 A and 48 MVA, respectively. ducting cables, assuming a voltage of 22.9 kV, which is Sumitomo Electric’s “3-in-One” superconducting cable the power distribution level in South Korea, a current of was installed in a 350-meter-long underground conduit 1,250 A, which is five times the standard capacity of 250 with an inner diameter of 6 inches (152 mm). The A, and installation in 175 mm diameter underground ducts in urban areas. The total budget for this research study project is about $6 million, 60% of which is funded by the South Korean government, and 40% by KEPCO. Electrical Insulation Stainless Steel Double The main subject of the study was to procure a supercon- (PPLP +Liquid Nitrogen) Corrugated Cryostat ducting cable through an international public bidding and operate it at the KEPCO testing site in Gochang, Cu Stranded Wire Former South Korea. Sumitomo Electric, who has experience in participating in a joint superconducting cable project 35mm 135mm with Tokyo Electric Power Company, had submitted a tender application and successfully won the public bid- ding for the KEPCO project. This was the world’s first Cu Shield commercial order of superconducting cable. Superconductor Superconducting Shield Table 3 and Fig. 6 respectively show the parameters (Double Layer)) (Single Layer) Tension Member and configuration of the the KEPCO Project supercon- ducting cable system. Tests such as long-term operation Photo 2. Three-cores-in-one-cryostat type Superconducting Cable Structure test and heat cycle test will be performed using this superconducting cable system to carry out technical and economical assessments.

Table 2. Specifications of Albany HTS Cable

Item Specifications Table 3. Cable System Specifications Former Stranded copper wires with insulation Item Specifications HTS conductor Double layer of BSCCO tape Rated voltage 22.9kV Electrical insulation PPLP (thickness: 4.5 mm) Rated current 1250A HTS shield Single layer of BSCCO tape Rated capacity 49.6MVA Copper shield Copper tapes Cable type 3-in-One superconducting cable 3-core stranding Loose 3-cores stranding Length 100m Thermal insulation Double-corrugated stainless steel pipe & Electrical insulation type Low temperature dielectric layer(Cable cryostat) multilayer vacuum insulation Termination EB-A (2 units) Protective outer Polyethylene/stainless-steel-tape tension sheath covering member Installation Tunnel & duct (30 m) Cable outer diameter 135mm Cooling system Liquid nitrogen circulation

SEI TECHNICAL REVIEW · NUMBER 65 · OCTOBER 2007 · 55 LN2 magnet with a 200 mm room-temperature bore (11). circulation system Applications of magnetic field to other magnetic Termination Termination Current trans. resonance analysis apparatus like MRI and NMR systems Voltage trans. are also under development, which are magnetic separa- LN2 return pipe tion and magnetic field control of molten metals. Tunnel Duct (3) Superconducting transformer HTS cable Superconducting transformer is considered as one of the applications of superconductivity to electric power systems. The advantages of using superconductor for Fig. 6. System Configuration transformer are low loss, compactness and light weight. The benefits of compactness and light weight are 3-3 Application of superconducting magnetic field that it can be used in movable bodies, and the applica- (1) Application of superconducting magnetic field tion of superconductor to transformers for high-speed The most basic application of superconductivity is trains is now under consideration. For Japanese superconducting magnets that can generate a high mag- Shinkansen bullet trains, reduction of weight is an netic field at a compact size. Other than superconduct- important issue, and superconducting transformer is ing magnets, superconducting magnetic field is used by expected as a means to achieve lighter weight. The trial transformers, motors and linear motors. 3.5-MVA-class superconducting transformer is shown in (2) High-field Photo 4 and the parameters are shown in Table 4 (12). Superconducting magnets are used for the genera- The transformer has enough capacity to be used in tion of high magnetic field which requires very large Shinkansen, but there remains another problem of AC electrical power when using non-superconducting mag- loss, which influences the weight of cryocooler. Because net. One example of commercial application of super- it is important to reduce AC loss, low AC loss supercon- conducting magnet is medical magnetic resonance ductor needs to be developed as soon as possible. imaging (MRI) that usually uses NbTi, a low-tempera- ture alloy superconductor. The maximum magnetic field obtained using NbTi is around 8 T. To generate a magnetic field over 8 T, an intermetallic superconduc- tor Nb3Sn has been used. For nuclear magnetic reso- nance (NMR), whose principle is the same as MRI but is used mainly for material analysis, higher field is required to have high resolution. When performing NMR at over 1GHz, a very high field of more than 23T is needed, but it is difficult to generate such high field with Nb3Sn. Therefore, superconducting magnet using BSCCO wire is under development. As for superconducting magnet that generates a magnetic field of around 10T, those commercially avail- able use low temperature superconductors, However, magnet using BSCCO superconductor that can be easily cooled using 20 K cryocooler has been also developed. Photo 3 shows a coolant-free 8.1 T superconducting

Photo 4. Superconducting transformer for railway rolling stock (Photo courtesy of Railway Technical Research Institute)

Table 4. Transformer specifications Primary voltage 25,000V Secondary voltage 1,200V (4 windings) (For driving) Tertiary voltage 770V (For servicing) 1.2m x 0.7m x 1.9m Dimensions (WxDxH) (excluding compressor) 1.7 ton Weight (excluding cryocooler and compressor) Cooling method Liquid nitrogen immersion

Photo 3. Superconducting magnet apparatus Wire BSCCO superconducting wire

56 · Examples and Future Prospects of High-Temperature Superconductor Products (4) Superconducting motor housing with a propeller directly connected to it The Japanese Maglev train using superconducting attached beneath the ship’s bottom, is increasingly magnets had set a world record of 581 km/hour. being adopted in luxury liners and ice-breaking boats. Conventional superconducting Maglev system used The ship with a pod propulsion system can change its NbTi superconductor and 4 K cryocooler, but a system direction freely, because the pod acts as a rudder. Using using BSCCO superconductor is now being researched superconducting motor, the pod can be made smaller at an experimental line constructed in Yamanashi and the overall propulsion efficiency will improve by Prefecture. Because the new system uses more effective around 30%. 20 K cryocooler, the stability against temperature fluctu- In Japan, an industry-academic consortium consist- ations can be increased and overall economic efficiency ing of Sumitomo Electric, University of Fukui, IHI and can be improved. other companies are developing the axial-gap type Since powerful superconducting magnet has superconducting motor for ship propulsion systems (13). become available, the development of a motor with (Photo 5) The most prominent feature of this super- greater efficiency and higher torque is expected. The conducting motor is that the motor is cooled by liq- advantage of such motor is especially prominent in large uid nitrogen as a result of the use of iron core. motor sizes. The conventional ship propulsion system is Conventional superconducting magnet generates a high that a diesel engine equipped with a gear and a shaft magnetic field by utilizing the high current density of causes a propeller to rotate. On the other hand, electric- superconductor, so the idea of using an iron core whose ity consumption in ships is increasing recently. The maximum magnetic field is around 1 T was unthinkable. rotating speed of a diesel engine should be quite low However, by determining the optimum location for iron even when a gear is used, so the engine is generally core, the drawback of the BSCCO superconductor is off- large. Therefore, for the purpose of maintaining the set and a small and lightweight motor is realized. balance of a ship, the engine is set in the center of the Presently the consortium is working to develop a 400- ship and rotational force is transmitted to the propeller kW-class superconducting motor. It is expected that if a using a long shaft. The new mechanism is that the contra-rotating propeller type propulsion system using motor is powered by electricity generated by the diesel two 400-kW motors is implemented in a several-hundred- engine. Because rotational force is converted into elec- ton-class ship, discharge of carbon dioxide will be tricity, the new mechanism may seem inefficient. reduced. However, the engine for power generation can operate at a higher rotation speed and therefore can be made in a smaller size compared with the engine for driving a shaft in achieving the same output power. Moreover, 4. Future prospects and problems because electricity is transmitted by cables, the location of the engine can be determined more flexible and the By achieving the characteristics improvement and space in the ship can be utilized effectively. Because the mass production of DI-BSCCO, it is expected that in the engine is small, it is easy to hydrodynamically optimize future DI-BSCCO will have about the same cost effec- the ship’s structure and thus improve total efficiency. tiveness as copper wires. For full-scale expansion of the In recent years, pod electrical propulsion system, superconductor market, the prompt development of which has an electrical motor installed in a pod-shaped superconducting devices is necessary Because power cables are one of the most impor- tant infrastructures, they are required to have a very high level of reliability over a long period of time. Through various in-grid demonstration tests like the Albany Project, data on reliability and economic effi- ciency are being accumulated. Recently in Japan, a new superconducting cable project led by the Ministry of Economy, Trade and Industry (METI) and the New Energy and Industrial Technology Development Organization (NEDO) had started. In this project, more data on demonstration under real operation conditions and on reliability will be collected. Demonstration of DC superconducting cable, which gets great perfor- mance out of superconductors, is also expected to be carried out in near future. Technology of DC low-volt- age power transmission is applicable to transmission of renewable energies like solar power and wind power. In the field of application of superconducting mag- net, development of practical ship propulsion motor is expected. The development of MW-class motor in addi- tion to 400-kW-class motor is planned. It is prospected Photo 5. Superconducting motor in the pod propulsion system that the global demand for reduction in carbon dioxide

SEI TECHNICAL REVIEW · NUMBER 65 · OCTOBER 2007 · 57 Table 5. Advantages of use of superconductor technology Low-Loss Lightness Compactness Torque Large Field High Accuracy Quietness Maintenance Stability Economy

Applicasions Purpose Remarks

MRI (Medical) High-Field Source ○ ○ ○ ◎ ○ Use of HTS in Remote Area Medical Care NMR Extreme High Field Source ○ ◎ ○ HTS for High-end machine Power Line Low Loss, High Power ◎ ○ ○ ○ ○ Many Government Projects For Shin-Kansen ○ ○ ◎ Lightness is the Most Important Issue Transformer Power Station ◎ ○ ○ ○ For underground substation MAGLEV Stable Operation ○ ○ ○ Remarkable System Cost Reduction Ship Propulsion Motor High Propulsion Efficiency ○ ◎ To Reduce Carbon Dioxide Emission Crystal Growth Larger Crystal ○ ◎ ○ ○ ○ Silicon, High-quality Steel Robot Larger Torque, Accuracy ○ ◎ ○ ○ ○ ○ Powerful & Accurate CNC Machine Accuracy, Maintenance ○ ◎ ○ Gear-less System Pharmaceutical products, Magnetic Separation ○ ○ ◎ ○ Installed in Paper Factory Wastewater purification

Vehicle Light Propulsion ○ ○ ◎ ◎ Suitable with Liquid Hydrogen System

Aircraft Light Propulsion ○ ◎ ○ ○ U.S. Air Force Wind Generator For smaller nacelle ○ ◎ ○ ○ ○ Light and Silent

emissions will accelerate the development of various (4) N. AYAI, M. KIKUCHI, K. YAMAZAKI, S. YAMADE, R. HATA, K. superconductivity-applied products. SATO, K. HAYASHI, T. KATO, J. FUJIKAMI, S. KOBAYASHI, E. UENO “Achievement of High-Temperature Superconducting Wire with Critical Current Exceeding 200 A”, SEI Technical Review No.63, p58-64 (5) N. Ayai, K. Hayashi, K. Yasuda, “Development of Bi-2223 5. Conclusions Superconducting Wires for AC Applications”, IEEE Trans. Appl. Supercond. vol.15 no. 2, p.2510-2513 Sumitomo Electric’s dynamically innovative DI- (6) M. HIROSE, Y. YAMADA, T. MASUDA, K. SATO, R. HATA “Study BSCCO has pushed the limits of critical current, on Commercialization of High-Temperature Superconductor”, mechanical strength and anti-ballooning properties. DI- SEI Technical Review No.62, p15-23 BSCCO is also innovative in that it may trigger the com- (7) H. YUMURA, T. MASUDA, M. WATANABE, H. TAKIGAWA, Y. mercialization of a wide range of superconductor prod- ASHIBE, H. ITO, M. HIROSE, K. YATSUKA, K. SATO, R. HATA, ucts. Table 5 shows the advantages and application “World’s First In-grid Demonstration of Long-length “3-in-One” examples of superconductor. Although various advan- HTS Cable (Albany Project)” SEI Technical Review No.64, p27-37 tages are expected in different areas, superconductor (8) US-DOE, “Grid 2030, A National Vision for Electricity's Second 100 years” must meet various requirements. By globally supplying (9) T. Masuda, Y. Yamada, “DEVELOPMENT AND DEMONSTRA- high-performance DI-BSCCO at reasonable prices, TION OF THE 3-IN-ONETM HIGH TEMPERATURE SUPER- Sumitomo Electric is determined to exploit the super- CONDUCTING POWER CABLE”, submitted to CIRED 2007 conductor market together with application product (10) M. WATANABE, T. MASUDA, H. YUMURA, H. TAKIGAWA, Y. developers. Sumitomo Electric will strive to act as an ASHIBE, H. ITO, C. SUZAWA, M. HIROSE, K. YATSUKA, K. SATO, evangelist of high temperature superconductor in order S. ISOJIMA, “Construction of 22.9-kV HTS Cable System for KEPCO to make the 21 century the century of superconducting Project in South Korea” SEI Technical Review No.63, p70-75 technology. (11) K. Ohkura, T. Okazaki, K. Sato, “Development of World’s Largest High-Temperature Superconducting Magnet with 20-cm-Diameter Room-Temperature Bore” SEI Technical Review No.65, p46-50 (12) H. hata, “Development of a newe Superconducting Main Transformer References for Trains” Railway Technoligy Avalanche No. 9, Aug. 2005 (1) K. Osamura, “Superconducting Materials”, Feb. 2000, p73 (13) T. Okazaki, “Study on Application of HTS Drive System for Movable (2) Cryogenic Association of Japan, “Handbook on Superconductivity Bodies”, SEI Technical Review No.62, p24-28 and Cryogenic Engineering”, Nov. 1993, p741 (3) T. KATO, J. FUJIKAMI, S. KOBAYASHI, K. YAMAZAKI, N. AYAI, K. FUJINO, E. UENO, M. KIKUCHI, S. YAMADE, K. HAYASHI, K SATO, “Development of Drastically Innovative BSCCO (DI- BSCCO) Wire”, SEI Technical Review No.62, p10-14

58 · Examples and Future Prospects of High-Temperature Superconductor Products Contributors (The lead author is indicated by an asterisk (*)) Y. YAMADA* • Assistant General Manager, Superconductivity & Energy Technology Department M. MOGI • Assistant General Manager, R&D Planning Department K. SATO • Dr. Eng., Fellow, General Manager, Materials and Process Technology R&D Unit

SEI TECHNICAL REVIEW · NUMBER 65 · OCTOBER 2007 · 59