Research, Fabrication and Applications of Bi-2223 HTS Wires

The following sections are included:

• Dedication
• Preface
• Table of Contents

Among a large number of cuprate superconductors, Bi-2223 is one of the well-developed one as superconducting tapes because of its high T_c, chemical stability and many other reasons. In this chapter, characteristic features of Bi-2223 are summarized and its superconducting properties as practical materials are compared with other superconductors. Furthermore, potentials of Bi-2223 materials are discussed from a viewpoint of controlling chemical composition.

The control of carrier doping level is essential for Bi-2223 wires to ensure high critical current (I_c) performance. Non-stoichiometric oxygen content is one of the most crucial factors to determine the carrier doping level. Bi-2223 wires were post-annealed in order to adjust the oxygen contents and their superconducting properties were investigated. The carrier doping level varied from under-doped to slightly over-doped states with the oxygen contents. A change of I_c limitation mechanisms in magnetic fields was confirmed at over-doped state.

The critical current (I_c) of Bi-2223 wires depends on magnetic field (B) and temperature (T). I_c depends on the history of external magnetic field (so called “hysteresis”) reflecting inter-grain weak coupling in Bi-2223 filament. I_c depends also on magnetic field direction (so called “anisotropy”) reflecting microstructure of Bi-2223 filament where plate-like Bi-2223 grains are aligned. In this chapter, typical I_c–B–T characteristics of Bi-2223 wires are described.

The electromagnetic properties such as critical current density and irreversibility field are described for superconducting Bi-2223 wires fabricated by the controlled over-pressure (CT-OP) process. The improvement of the critical current density was more significant in the magnetic field parallel to the tape surface than in the normal field. This improvement is limited in the low magnetic field region and the irreversibility field was not improved by this process. The observed properties are analyzed using the theoretical model of flux creep and flow. It is found that the improvement of the properties by introducing the CT-OP process is mainly ascribed to the improvement of the crystal alignment by the high pressure, while the pinning mechanism is unchanged.

In most alternating current (AC) power devices, Bi-2223 wire should carry an AC transport current under an AC external magnetic field, and transport losses due to transport current and magnetization losses due to external field are simultaneously generated in the wire. The magnitude of losses and difficulty of the loss reduction are strongly influenced by the direction of external field against the broader face of a tape-form Bi-2223 wire. In this article, the AC loss characteristics of Bi-2223 wire carrying a current in a transverse external field is shown and contribution of both transport and magnetization losses in total losses is briefly discussed. In addition, demonstration of the magnetization loss reduction under a transverse field in perpendicular to the broader face of the wire is described.

The characteristics of tensile properties of commercial Bi-2223 wires were explained by using the rule of mixture below the reversible strain limits. The reversible tensile strain limit coincides well with the start of degradation in critical current, because both phenomena have the same origin, at which the SC filaments start to fracture macroscopically. In order to improve both properties, it is crucial to maximize the reversible strain region. Its strategy was discussed in terms of thermal strain and pre-strain dependence through the strengthening by lamination.

We introduced the thermal conductivity κ(T) of Bi-2223 wires sheathed with Ag-based alloys. The thermal conductivity of several sheathed Ag-based alloys was also summarized. For several kinds of DI-BSCCO tapes, κ(T) was reported and the anisotropic thermal conductivities of the stacked or sandwiched DI-BSCCO bundles were measured and analyzed using the heat flow model. The κ(T) data are useful and valuable for calculating the heat intrusion and thermal stability for the application to the superconducting coils and power current leads.

The review novel approaches are presented to describe quench/heat developments in HTS Bi-2223-based devices. These approaches permit determination of thermal stability level for both: Uniform and non-uniform heating of HTS devices, particularly during overheat conditions. Thermal quench/thermal runaway current and characteristic time of heating development can be evaluated. At non-uniform heating blow-up, regimes with temperature localization could happen that should be taken into account by HTS cables designers. Review of studies of cooling of HTS wires by boiled liquid nitrogen is also presented.

To investigate the potential of high T_c Bi-2223 superconductors, as well as the growth mechanism of Bi-2223 phases, Bi,Pb-2223 thin films were fabricated by a combination of sputtering and annealing methods. The resulting films had J_c values almost one order of magnitude greater than those reported for wires. The growth mechanism by which a Bi-2223 single phase is obtained is highly complex since this material contains six elements, and many impurity phases may be present. Studies of thin films such as those detailed herein assist in understanding this growth mechanism.

This chapter reviews Ag-sheathed (Bi, Pb)₂Sr₂Ca₂Cu₃O_x (Bi-2223) wire made by the powder-in-tube technique (PIT). The currently leading high-temperature superconductors (HTS) wire technology for practical use is Bi-2223 wire, made by the controlled over-pressure (CT-OP) sintering process. The CT-OP process uses pressures up to 30MPa during heat treatment. The technique densifies the Bi-2223 filaments and enhances the uniformity of the electrical and mechanical performance in the Bi-2223 wire. Today, Bi-2223 wires are used in most HTS applications, such as power cables, many kinds of magnets, and motors for ship propulsion and electric vehicles.

In terms of the ideal microstructure for Bi-2223 wires with high I_c performance, Bi-2223 volume fraction along with distributions of impurity phases and Bi-2223 grain alignment were reviewed. This chapter summarized the characteristics of the present available wires, which had over 95% of Bi-2223 volume fraction and the degree of texturing ~6°. The results showed that there were many issues to address for further improvement of microstructure, though the wire had high I_c, enough for the current application use.

The technology, engineering science and motivation for laminating metal strips onto Bi-2223/Ag tapes are reviewed. The approach allows for the production of Bi-2223/Ag tape with high critical current (I_c) that can be laminated with many types of thin metal strips in order to improve axial stress, strain, bend, and surface indent tolerance as well as mitigation of cryogen penetration and thermal instability. Advances to attain target mechanical properties are enabled by an analytical model that identifies required modifications to internal stress, strain, and failure modes. The model also enables the selection of materials, architectures and process parameters for producing very robust tape. In a recent advance, laminated super alloy strips increased Bi-2223 tape axial stress tolerance from 120MPa to 540MPa, and axial strain tolerance from 0.25–0.4%, with a 30% reduction in whole wire current density from the added strip areas, but with no reduction in I_c.

Activity of quality assurance of commercial Bi-2223 wire, Bi, Pb(2223) wire as described in this chapter, is introduced, and the specifications of the spliced wire are proposed. Statistical data and experimental data related to wire specifications are discussed based on the probability theory. Detecting the defects for protection against the quench is a highly important task for Bi, Pb(2223) wire quality assurance. The method of electrical inspection such as critical current I_c and n-value is explained. For inspecting the uniformity of the wire, the hall probe measurement method has been developed. Uniformity of the critical current of Bi, Pb (2223) is discussed.

Bi-2223 High Temperature Superconductivity (HTS) wires use certain amount of silver. Recently there is a new wire which has less silver than before. People say that Bi-2223 wire is expensive, because it uses silver. However, silver contributes a lot in terms of stable quality of Bi-2223 HTS wires and silver is necessary for its performance. This paper summarized the actual value of silver in the wire and compares the copper value in the copper cable system and the silver value in the HTS cable system using an example of cable project in Germany.

According to the procurement agreement between International Thermonuclear Experimental Reactor International Organization (ITER IO) and China Domestic Agency (CNDA), Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP) is responsible for the design, fabrication and testing of a series of high temperature superconducting (HTS) current leads (CLs) for ITER since 2007. Three types of HTS CLs have been developed, manufactured and tested, which contain a cold section based on the use of Bi-2223/Silver–Gold alloy tapes and helium forced cooling resistive part optimized for the rated current operations at 68kA, 55 kA, and 10 kA. In this chapter, an outline of the design of the leads is presented, together with the manufacture and testing at ASIPP.

A current lead (CL) for conduction-cooled magnets or cryocooled superconducting magnets (CSM) is required to have small heat leakage from high temperature stage to low temperature stage and sufficient strength against electromagnetic force (Lorentz force) and thermal stress. A high temperature superconductor (HTS) has high critical temperature, and the thermal conductivity is lower than the normal conductor. This chapter will show the configuration and design of the CL for CSM using Bi-2223 HTS wire.

Superconducting Fault Current Limiter (SFCL) is one of the most promising applications of HTS for electric power industry. Through years of innovative improvement, saturated iron-core type SFCL is one of the most prevailing technologies in SFCL R&D around world.

In this chapter, the working principle, typical structure and key components of a saturated iron-core type SFCL is introduced. Functional characteristic, grid operation performance and test results are also presented. This kind of device is applicable for both transmission and distribution networks and can satisfy a wide range of fault current limiting impedance requirements.

Among the wide range of High-Temperature Superconducting (HTS) materials presently known Bismuth Strontium Calcium Copper Oxide (BSCCO) is a very suitable candidate for power applications either at low temperature (e.g. <30K) at any field or at high temperature (e.g. 77K) in self-field conditions. This is due to several advantages of BSCCO from an electrical, thermal, mechanical and economic point of view. In particular, BSCCO has been proven to be particularly suitable for hybrid current leads and HTS cables. However, BSCCO-based Superconducting Fault Current Limiter (SFCL) applications have been an important issue within the Ricerca sul Sistema Energetico (RSE) S.p.A. R&D portfolio in the last decade. The SFCL project, funded in the framework of a R&D national project, started focusing on a preliminary single-phase device, which was submitted to dielectric and short-circuit current testing. The first success paved the way for the finalization of the remaining two phases and the final result was a three-phase resistive-type 9 kV/3.4 MVA SFCL device, based on first generation (1G) BSCCO tapes that was installed in the S. Dionigi substation, belonging to the Italian utility A2A Reti Elettriche S.p.A. (A2A), in the Milan MV distribution grid. The in-field activity lasted for more than two years, demonstrating the SFCL capability to cope with the grid in every-day operating conditions. Moreover, at the end of the experimentation, the SFCL device was able to perform a true limitation during a three-phase fault, thereby becoming one of the first SFCL devices in the world (the first in Italy) installed in a real grid and to have limited a real short-circuit current.

This chapter will give an overview on the German AmpaCity project, which started in September 2011. The objective of the project is developing, manufacturing and installing a 10 kV, 40MVA HTS system consisting of a fault current limiter and of a 1 km cable in the city of Essen. It is the first time that a one kilometer HTS cable system is installed together with an HTS fault current limiter in a real grid application. In addition, it is the longest installed HTS cable system worldwide. Within the project the development phase was finished in March 2013 with successfully completing the type test of the cable system. Subsequently, all system components were manufactured for the installation on site in Essen. The installation took less than three months finishing at the end of November 2013. Afterwards, the commissioning test of the system was performed in December and the system was finally commissioned beginning of 2014.

High Temperature Superconducting (HTS) cables can transmit large amounts of electricity in a compact size with minimal losses. Therefore, they are expected to save the construction cost of underground lines in urban areas and decrease transmission losses. Several HTS cables have recently been demonstrated in networks around the world, and full-scale commercialization is expected in the near future. In Japan, the development of compact HTS cables suitable for urban deployment has been underway since the early 1990s. In 2007, a national project was started to verify their operational performance and long-term reliability in the grid. An HTS cable 240 m long was installed at the Asahi substation of the Tokyo Electric Power Company (TEPCO) in Yokohama; then a joint, terminations and cooling system was constructed in 2011. After successful performance tests, the cable was connected to the grid for the first time in Japan, and started to deliver electricity to 70,000 households in October 2012. This trouble-free in-grid service continued for over a year. We can conclude that the HTS cable system performs well and has the stability required for long-term in-grid operations.

The Russian program for R&D of AC power cables has been started in 2005. During the program, the several 5m prototypes and witness samples of Bi-2223 based cables have been tested, as along with the 30m experimental three phase cable. Eventually 200m full size AC power cable with ratings 20 kV 1.5/2kA and 50/70MVA has been developed and successfully tested. The review of cable designs and test results is presented.

The internet data center (iDC) is becoming one of the most important and widespread infrastructures in modern life, but it consumes electrical power plentifully. The reduction of its electric power consumption is an urgent subject. A Direct current (DC) power systems are now being applied. The DC high temperature superconducting (HTS) power cable is well-suited for such systems and is a suitable application in applied superconductivity. Subjects of the superconducting power cable system are discussed, especially about the cable design and the heat leakage of the current lead. Several ideas are proposed and discussed for the future iDC using HTS power cable and renewable energy (RE) system.

Superconducting cables have evident benefits when transmitting large power flows through electrical networks in comparison with traditional ones. However, the use of DC superconducting cable lines together with converters brings additional advantages like reduction of losses in cables and suitable lowering of refrigerating plant capacity, as well as the realization of the function of short-circuit currents limitation by means of the appropriate setting of converter equipment. The presence of the current limitation function makes it possible to use such lines for the connection of megalopolises' power network sectors at the medium-voltage side without increasing the short-circuit currents.

With the quick development of renewable energy, it is expected that the electric power from renewable energy would be the dominant one for the future power grid. Due to the specialty of the renewable energy, the HVDC power transmission would be very useful for the transmission of electric power from renewable energy. DC power cable made of High T_c Superconductor (HTS) would be a possible alternative for the construction of HVDC power transmission system. In this chapter, we report the development and demonstration of a 360 m/10 kA HTS DC power cable and the test results.

The development of a superconducting cable for railways has commenced, assuming that a DC transmission cable will be used for electric trains. The cable has been fabricated based on the results of current testing of a superconducting wire, and various evaluation tests have been performed to determine the characteristics of the cable. A superconducting transmission cable having zero electrical resistance and suitable for railway use is expected to enhance regeneration efficiency, reduce power losses, achieve load leveling and integration of sub-stations, and reduce rail potential.

High-temperature superconducting (HTS) cables are expected to resolve technical problems with power grids because they put large-capacity, low-loss power transmission into a compact package. One problem is replacing old 275-kV oil filled (OF) cables with cross-linked polyethylene insulated vinyl sheath cables (XLPE cables). This is difficult because XLPE cable has a lower transmission capacity than OF cable. In addition, the high concentration of public infrastructure underground makes it extremely difficult to build new ones. However, if 66-kV HTS cables can be installed inside existing underground conduits and can achieve a power capacity equivalent to conventional 275-kV cables, construction costs could be significantly reduced. Moreover, if XLPE cables are used for a 1,000 MVA-class transmission line, then three circuits of nine 275-kV single-core cables would be required, which would incur a transmission loss of 90 W/m/cct. Three circuits of three 66-kV Three-in-One HTS cables, however, with an AC loss of 1 W/m/ph@3 kA, heat invasion of 2 W/m, and cooling system efficiency of 0.1, would reduce transmission loss to less than three-fifths that of XLPE cables.

Recent rapid demand increase and supply decrease for helium has raised the price in these years. Superconducting magnetic resonance imaging (MRI) magnets, which consume 20% of global production of helium as the cryogen, are therefore expected to be helium-free and high-temperature superconducting (HTS) materials are potent candidates to realize this. Because of the reason, we developed a cryogen-free 3T-MRI scanner for human brain research using Bi-2223 tapes. For scanning a subject in sitting position, a vertical bore was adopted. The magnet was designed for operating temperature of 20 K and for driven mode. Both target homogeneity and stability of the magnetic field in field of view (FOV) region were within 1 ppm. Not only the magnet but also the other important hard/softwares were produced by us. After the assembly, adjustments and imaging experiments with the scanner were carried out at 1.5 T successfully. Although ramp-up to 3 T succeeded three times, successive abnormal events happened for longer than ten minutes during the third ramp-down time, and finally the magnet got fatal damages. Here, we introduce the system and discuss on problems and potentials of HTS-MRI magnets.

The use of a Bi-2223 magnet provides a high current density above 23 T, enabling a nuclear magnetic resonance (NMR) magnet to exceed a magnetic field of 23.5 T (1 GHz). The development and perspectives of super high field (LTS)/Bi-2223 NMR spectrometers that can operate at fields as high as 1.2 GHz NMR are described.

Over the last decade significant progress has been made in the commercialization of HTS magnets, paralleling the improvements in wire performance and quality. In this chapter, we review the development at HTS-110 of magnets for synchrotron and neutron beamlines which leverage the benefits of high current density relative to copper and a relatively high operating temperature compared to the low-temperature superconductors. New products extending this development into the demanding realm of magnetic resonance are also discussed.

Conduction-cooled magnets are useful and easy to operate. Their advantages and their configuration and application are explained. The technique required to protect the magnet is also described.

We are developing a Bi-2223 HTS dipole magnet for beam line switching for use in the cyclotron facility of RCNP, Osaka University. Exit beam lines are periodically switched by increasing and decreasing of the magnetic field between 0 T and 1.6 T with a switching time of 10 sec. A Bi-2223 coil assembly was designed with the electromagnetic force support and the suppression of temperature rise by AC loss and eddy current loss. In this chapter, we introduce this magnet as a practical example of conduction-cooled Bi-2223-HTS magnet for accelerator application.

Compact and light weight direct-drive machines in large rating are desired as ship propulsion motors, and as generators for off-shore wind farm applications. A key goal for such machines is to be shipped to the site as fully assembled units. In order to achieve this goal, it is essential to construct both rotor and stator windings also using high-temperature superconducting (HTS) materials. Two commercially available HTS conductors are Bi-2223 (Bi₂Sr₂Ca₂Cu₃O) HTS with a critical temperature of about 110 K, and Magnesium Diboride (MgB₂) with a critical temperature of about 40 K. The MgB₂, available in small diameter wires, is suitable for manufacturing stator coils operating in high AC magnetic field environment. This chapter presents a concept design for a 40 MW, 120-RPM ship propulsion motor employing Bi-2223 for field winding and MgB₂ for stator winding. Ambient temperature magnetic iron is employed on the rotor and the stator. The field winding consists of race track shaped Bi-2223 coils operating at 35 K. The stator winding, made up of MgB₂ race track coils, operates at 20 K. Available off-the-shelf cryo-coolers are used for cooling all coils. The concept 40 MW motor is expected to be about 3 m in diameter, 2.3 m in axial length, and weigh around 80,000 kg. The design approach discussed here could also be used for designing large rating generators for wind farm applications.

IHI corporation succeeded the trial manufacture of the world's first 12.5 kW motor with superconducting armature windings cooled by liquid nitrogen (LN₂) in January 2005. With the aim of the practical application of larger-scale motors, various technical problems peculiar to the axial-gap motors with superconducting armatures have been solved, for example, cryostats, AC losses, and so forth. Then, we completed load tests on the motors with the rated power of 400kW, which are at present the world's largest in LN₂-cooled superconducting motors. The features of those motors and technical breakthroughs are described in this chapter. Problems for their practical applications are also discussed.

The KHI team has developed radial gap high-temperature superconducting (HTS) motors of three sizes, 1 MW-class, 3 MW, and 20 MW, to be used for electric propulsion systems for ships. The volumetric torque density of the assembled 3 MW HTS motor was recorded at 40 kNm/m³ in the load test; the world's highest in the class.

Rotating principle and fundamental performance of high temperature superconducting induction/synchronous motor employing Bi-2223 tapes are reviewed. Development status of 20kW class prototype motors is also introduced, and then the future perspective of the motors to the next generation automobile is discussed.

In recent years, electrification of automobiles is in progress. Following the advent of passenger electric vehicles, large size commercial vehicles with electric drive are also being developed. One of the problems in the development of large electric vehicles is the heavy weight which leads to short driving distances. Energy saving by the use of high-efficiency motors will be a solution. The authors have developed a prototype electric vehicle equipped with a high-temperature superconducting (HTS) motor and a refrigerator. The test results showed that the motor has torque of 136 Nm and an output of 30 kW, and the prototype vehicle obtains the maximum speed of 80 km/h.