HTS Wire Research Articles

Characteristic comparison of different resonators to extend transfer distance in superconducting wireless power transfer for electric vehicle using high temperature superconducting resonance coil

AbstractThis paper presents the feasibility of technical fusion between wireless power transfer (WPT) based on resonance coupling system and superconducting technology to improve the transfer efficiency and spread the electromagnetic field widely in spite of small size coils. Until now, the various copper wires have generally been adopted in WPT system. From this reason, the transfer efficiency is limited since the copper wire keeps low Q intrinsically. On the other hand, as superconducting wires keep larger current density and higher Q value, the superconducting resonance coil can be expected as a reasonable option to deliver large transfer power as well as improve the transfer ratio since it exchanges energy at a much higher rate and keeps stronger magnetic fields out. In this study, we examined the transmission ratio using HTS and cooper wires in the antenna (Tx) or/and receiver (Rx) within input power of 500 W under various performances; copper Tx to copper Rx, HTS Tx to copper Rx, copper Tx to HTS Rx...

Winding and Testing of YBCO Coils Using Different HTS Wires

YBCO coils with epoxy resin impregnation tend to experience degraded performance, which is due to the mismatch of the thermal contraction coefficients among former, epoxy, and HTS conductors which will generate thermal stresses that induce delamination of the superconducting layer. Several coils have been fabricated and tested, using the YBCO wires from SuperPower Inc. (SP), and Shanghai Superconductor Technology Corporation (SSTC). No degradation of the coil performance was detected for small SP coils, even with epoxy resin impregnation. However, for SP coils and SSCT coils using more than 100 m of YBCO wires, they all exhibited degraded performance after the epoxy resin impregnation. A possible solution to this problem is proposed and a 400 m SSCT coil has been successfully fabricated and tested.

Design, fabrication and testing of a dipole magnet made with 2G HTS wire

An HTS dipole magnet with a 1 T (at 77 K) central magnetic field in a 40 × 80 mm2 aperture has been designed, fabricated and tested. The magnet coils were wound with SuperOx 2G HTS wire. The paper describes the magnet design, properties of the magnet materials, and results of calculations and measurements. The central field in the dipole reached 1.12 T at 77 K and 1.66 T at 65 K. In a liquid helium bath the maximum input current of 847 A was limited by the capacity of the power supply, and in that case the central field was 3.03 T. The measurement data were in good agreement with the calculation results.

Test Results of Gas-Cooled Prototype Magnet for In-Flight Fragment Separator

The first quadrupole magnet at the in-flight fragment (IF) separator of heavy ion accelerator should withstand intense radiative heat load of neutron beam. Most of the HTS magnets are cooled by liquid cryogen or conduction cooling methods. However, the quadrupole magnet is exposed to the intense radiation heat load, and the quadrupole magnet can be cooled by the circulation of cold gaseous helium. The gaseous helium cooling system is composed of a liquid nitrogen precooler, a recuperator, a compressor at room temperature, and a single-stage GM cooler. Nichrome wire inside bobbin simulates the radiative heat load by neutron beam. The prototype magnet consists of two single pancake coils and has the half length of the full-scale HTS quadrupole magnet. HTS wire is wound on an aluminum bobbin without insulation layer. This paper describes the thermal stability test results of the prototype HTS magnet using additional heater to simulate the large radiation heat load. The operating current is transported while applying the additional heating on the bobbin surface, and the thermal characteristic is investigated. The experimental data will be used to design the thermal structure of the HTS magnets used in the first quadrupole magnet at the IF separator.

Effects of Stabilizer Thickness of 2G HTS Wire on the Design of a 1.5-MW-Class HTS Synchronous Machine

In general, a metallic stabilization layer is overcoated on the outermost layer of a second-generation high-temperature superconducting (2G HTS) wire to stably transfer current against thermal and magnetic disturbances. Stabilizer thickness $T_{{s}}$ is one of the key issues in an HTS synchronous machine (HTSSM) application because it strongly affects the electrical output performance of the machine and the stable operation and reliable protection of the HTS field coil. In this paper, a design and characteristic analysis for manufacturing a 1.5-MW-class HTSSM was performed using a 2-D analytical design code and a 3-D finite-element method. Various $T_{{s}}$ values were considered in the HTS field-coil design to investigate their effects on the stability and protection of the HTS coil and the back-electromotive force of the machine. The design parameters are also discussed to determine suitable $T_{{s}}$ for the 2G HTS wire.

Performance and analysis of wireless power charging system from room temperature to HTS magnet via strong resonance coupling method

The technology of supplying the electric power by wireless power transfer (WPT) is expected for the next generation power feeding system since it can supply the power to portable devices without any connectors through large air gap. As such a technology based on strongly coupled electromagnetic resonators is possible to deliver the large power and recharge them seamlessly; it has been considered as a noble option to wireless power charging system in the various power applications. Recently, various HTS wires have now been manufactured for demonstrations of transmission cables, motors, MAGLEV, and other electrical power components. However, since the HTS magnets have a lower index n value intrinsically, they are required to be charged from external power system through leads or internal power system. The portable area is limited as well as the cryogen system is bulkier. Thus, we proposed a novel design of wireless power charging system for superconducting HTS magnet (WPC4SM) based on resonance coupling method. As the novel system makes possible a wireless power charging using copper resonance coupled coils, it enables to portable charging conveniently in the superconducting applications. This paper presented the conceptual design and operating characteristics of WPC4SM using different shapes' copper resonance coil. The proposed system consists of four components; RF generator of 370 kHz, copper resonance coupling coils, impedance matching (IM) subsystem and HTS magnet including rectifier system.

Solution deposition of ultrasmooth alumina on long-length metallic substrate for 2G superconducting tapes

Chemical solution deposition of smooth amorphous Al2O3 thin films has been successfully used for planarization of long-length metallic substrates for 2G HTS superconducting wires production. A series of metal-organic precursors based on Al(iPrO)3, Al(acac)3, acetic acid, monoethanolamine (MEA) and diethylenetriamine (DETA) was developed. Correlations between the precursor composition and the features of its two-step thermal-induced transformation to amorphous Al2O3 were studied by 1H NMR, IR spectroscopy and thermal analysis. Utilizing the solutions of {Al(iPrO)3+2.5MEA+6HAcet} in iPrOH and {Al(acac)3+nDETA} in HAcet (n=1−3) as precursors for dip-coating, we obtained the long-length Hastelloy C276 substrate covered by uniform amorphous 50–550nm thick alumina films with surface roughness of about 0.5–1.5nm. A 20m long sample of 2G HTS wire with a commercial level of superconducting critical current of up to 300A was prepared based on Hastelloy substrate tape planarized with Al2O3.

Customised 2G HTS wire for applications

Reproducibility of superconducting properties and suitability for specific applications by means of customised finish are two important attributes required from commercial 2G HTS wire. This paper reviews the consistent performance of SuperOx production 2G HTS wire and describes two novel customisation options: surround polyimide varnish insulation and composite bulk materials assembled with 2G HTS wires soldered together.

Analysis on the Degradation Characteristics of 2G High-Tc Superconducting Wires in Accordance with Electrical Breakdown Voltage

Recently, extensive studies have been carried out on developing a high voltage superconducting apparatus as a substitute for the conventional one. superconducting wires used for a high voltage superconducting apparatus can be damaged under high voltage condition due to electrical breakdown and the damaged superconducting wires may result in the degradation of the critical current (Ic) and index number. Therefore, a study on the degradation characteristics of superconducting wires in accordance with the electrical breakdown should be performed. In this paper, the degradation characteristics of second generation high temperature superconducting (2G HTS) wires with respect to electrical breakdown tests are studied. The applied electrical breakdown voltages to 2G HTS wire are AC and lightning impulse (Imp) ; 50, 60 and 70 kV. The electrical breakdown test is successively repeated five times. The Ic and index number of 2G HTS wires were measured. The relationship between electrical characteristics such as the Ic and index number and the electrical breakdown was analyzed.

사고전류 인가 시 초전도선재의 상전도-초전도 접합부가 통전전류와 ?치저항에 미치는 영향

The second-generation HTS wire its YBCO coated conductor is widely used in the superconducting power apparatus. The YBCO coated conductor uses the normal-superconducting junction to increase the transport capacity of superconducting power apparatus when it is applied. The normal-superconducting junction can be a cause of reducing the stability of the superconducting power apparatus when a fault current is applied. Thus, in this study we have conducted the effect analysing normal-superconducting junction for the fault current using transport current and quench resistance. From the experimental results when a fault current is applied, the effect on the normal-superconducting junction is reduced the larger the amplitude of the fault current and is helpful to maintain the thermal stability of the HTS wire.

Low-Temperature Scaling of the Critical Current in 1 G HTS Wires

We present highly detailed temperature, magnetic field and field angle dependent measurements of the critical current of a state-of-the-art commercial first-generation Bi-2223 high temperature superconductor wire (Sumitomo new type H high current density DI-BSCCO). By scaling the applied field values at different angles using the Blatter electron mass anisotropy expression, we demonstrate that the measurements at each temperature from 20 to 85 K collapse onto a common curve with respect to the scaled magnetic field. However, the scaling parameter is found to range from 7 at 80 K to 13 at 25 K, far below the values reported in the literature for the electron mass anisotropy of this material, and far closer to the values reported for similar analyses of data obtained from the much less anisotropic superconductor YBCO. This suggests that a mechanism of similar magnitude underlies and determines the results obtained for both materials in spite of their greatly differing electronic mass anisotropies. By normalizing the results to the self-field critical current and the irreversibility field, we are able to obtain a single universal curve describing the performance of the superconductor across the full range of operating conditions. In contrast to pinning-engineered YBCO coated conductors, we find that the low-temperature behavior of BSCCO wires can be well correlated with its high-temperature behavior. Knowledge of this straightforward behavior of this commercial superconductor across the full parameter space of temperature, field and field angle will be invaluable to engineers working with this material to construct machines or devices.

Study on Influence of Repeated Hoop Stresses on HTS Wires in Coils

HTS wires in coils are subjected to hoop stresses due to electro magnetic forces and thermal contractions. Influence of repeated and non-repeated hoop stresses is investigated by making an experimental apparatus to apply hoop stresses mechanically to dry (non impregnated) and epoxy-impregnated HTS test coils. In the experiment it was found that a critical current of a dry coil was more degraded by the hoop stresses than that of an epoxy-impregnated coil. In the paper, distribution of hoop stresses to layers in HTS coils are investigated and based on the experimental results, differences of critical current degradations of dry and impregnated coils are studied.

Design Consideration and Efficiency Comparison of Wireless Power Transfer With HTS and Cooled Copper Antennas for Electric Vehicle

The wireless power transfer (WPT) technology based on strongly resonance coupled method realizes large power charg- ing without any wires through the air. Recently, the WPT systems have started to be applied to the wireless charging for electri- cal vehicles (EVs) because of their advantages compared with the wired counterparts, such as convenience, safety, and fearless transmission of power. However, it has obstacles to commercialize such as delivery distance and efficiency. To solve the problems, we proposed the technical fusion using a high-temperature super- conducting (HTS) antenna in the WPT system, which is called superconducting WPT for electric vehicle (SUWPT4EV) system. Since the superconducting wire has the merits of a larger current density and higher Q value than a normal conducting wire, the HTS antenna enables to deliver a mass amount of electric energy in spite of a small-scale antenna. To apply copper-stabilizer HTS (GdBCO) coil for EV charging system practically, the transfer efficiency characteristics for the HTS wires should be investi- gated. In this study, we examined transfer characteristics with copper-stabilizer HTS antenna at 77 K and copper antenna at 77 K, respectively. The transfer distance is at 30 cm, and RF power of 370 kHz below 500 W is adopted. Moreover, in order to improve the transfer efficiency, the design considerations for the SUWPT system were described. Index Terms—Cooled copper antenna coil, electric vehicle, electromagnetic resonance coupling, high-temperature supercon- ducting (HTS) antenna coil, superconducting contactless power transfer.

An Experimental Investigation of Critical Current and Current Distribution Behavior of Parallel Placed HTS Tapes

The AC superconducting power transmission cable projects are being carried out around the world, while the DC superconducting cable is also proven to be very competitive for power transmission in electrical grid due to the negligible AC losses. The critical current and current distributions are two important factors to improve the performance of DC HTS cable for large transmission capacity. In this paper, we proposed an experimental method to investigate the behavior of critical current affected by various gap distances between the individual HTS tape and transverse tape width. The results show that the critical current of the HTS tape in the cable field can be increased by about 10% if the gap distance is less than 1 mm. Finite element method (FEM) is used to calculate the magnetic field distribution to verify the experimental results. A short HTS cable has been constructed to investigate the influence of contact resistance on the current distribution among the HTS tapes. The results show that the contact resistances have significant influence on the current sharing of each HTS wire in the cable structure.

Future Upgrade of the Superconducting High Field Facility HOMER II to 25 T

In 2006, the superconducting high field facility HOMER II of the Karlsruhe Institute of Technology was commissioned. It provides a magnetic field of 20 T in a large bore of 185-mm diameter, using a coil system with sections made of NbTi and (NbX)3Sn wires. With regard to the increasing availability of high-quality second-generation high temperature superconductors (2G-HTS) in longer lengths, in 2014, the project for an intended upgrade of HOMER II to a total field of 25 T has been started. The objective is to build up a 5-T insert made of REBCO HTS to be operated routinely in the background of 20 T produced by the basic magnet configuration of HOMER II. In this paper, we report on the schedule of the project, the preliminary design of the HTS-insert, and the requirements for the HTS wire. Furthermore, the results of the preparatory operation of small solenoid HTS coils in the 20-T background field are presented.

Magnetic structural effect (MSE) in epitaxial films of cerium oxide and lanthanum zirconate

Increasing the critical current density in the second generation high-temperature superconducting wires (2G HTS) is the major challenge for researchers and manufacturers of 2G HTS wires all over the world. We proposed a new approach to increase the number of percolation paths for supercurrent, i.e. increasing the number of low angle grain boundaries (<5°) in the epitaxial superconducting YBCO layer by magnetic structural processing (MSP) of buffer layers. New experimental results have been presented on the application of MSP for improving the structure and increasing the texture sharpness of buffer in electrical conducting element of 2G HTS wire. The influence of MCO on the structural and textural properties has been investigated in a buffer consisting of epitaxial films of cerium oxide CeO2 and lanthanum zirconate La2Zr2O7 in the CeO2/4La2Zr2O7 architecture. The influence of the magnetic processing of the epitaxial La2Zr2O7 buffer film on the shape of grains has been found. An atomic force microscopical study has shown that after magnetic processing the shape of grains improved significantly. A multilayer CeO2/4La2Zr2O7 buffer each layer of which was processed in a magnetic field has a high degree of orientation: only one diffraction peak with (200) indexes is observed in the X-ray spectrum. The X-ray settings of the (200) diffraction peak indicate a well developed epitaxial structure of CeO2 and La2Zr2O7 layers. The texture of the buffer is by more than 2° sharper than that of the Ni–5at% W substrate.

MAGNETIC STRUCTURAL EFFECT (MSE) IN EPITAXIAL FILMS OF CERIUM OXIDE AND LANTHANUM ZIRCONATE

An increase of the critical current density in the second generation high−temperature superconducting wires (2G HTS) is the major challenge for researchers and manufacturers of 2G HTS wires all over the world. We proposed a new approach to increasing the number of percolation paths for superconducting current, i.e. increasing the number of low angle grain boundaries (<5°) in the epitaxial superconducting YBCO layer by magnetic structural processing (MSP) of buffer layers. New experimental results have been presented on the application of MSP for improving the structure and increase the texture sharpness of buffer in electrical conducting element of 2G HTS wire. The influence of MCO on the structural and textural properties has been investigated in a buffer consisting of epitaxial films of cerium oxide СеО2 and lanthanum zirconate La2Zr2O7 in the СеО2/4La2Zr2O7 architecture. The influence of the magnetic processing of the epitaxial La2Zr2O7 buffer film on the shape of grains has been found. A study under an atomic force microscope has shown that after magnetic processing the shape of grains improved significantly. A multilayer CeO2/4La2Zr2O7 buffer each layer of which was processed in a magnetic field, has a high degree of orientation: only one diffraction peak with (200) indexes is observed in the X -ray spectrum. X -ray settings of diffraction peak (200) indicate a well developed epitaxial structure of CeO2 and La2Zr2O7 layers. The texture of the buffer is by more than two degrees sharper than that of the Ni−5 at.% W substrate.

Calibration of a HTS Based LOX 400 mm Level Sensor

The measurement of the cryogen level in a cryostage of space crafts is crucial. At the same time the weight of the sensor should be small as it affects the payload fraction of the space craft. An attempt to develop a HTS based level sensor of 400mm for Liquid Oxygen (LOX) measurement was made. In the initial phase of testing, loss of superconductivity of HTS wire in LOX inside a cryostat was noticed. Thus, a new four wall cryostat was designed to have a stable LOX level to provide thermal stability to the HTS based LOX sensor. The calibration of the developed sensor was carried out against capacitance level sensor which was pre calibrated using diode array to verify its linearity and performance for different current excitation levels. The calibrations were carried out without heater wires. The automatic data logging was accomplished using a program developed in LabVIEW 11.0.

Vision Inspection Methods for Uniformity Enhancement in Long-Length 2G HTS Wire Production

With much effort devoted by many research groups, the performance of 2nd generation (2G) superconducting wires, also called coated conductors (CC), was drastically improved, leading to many meaningful and impressive demonstrations of electric power devices. Now that the performances such as critical current, in-field characteristics, and mechanical strengths became sufficient to the application, the attention has moved to how we can produce long 2G wires with high uniformity. Many in-line inspection tools are tested and introduced to address these challenges. In this paper, we describe two methods that we adopted for in-line monitoring and feedback control of layer deposition. One is for texture control of ion beam assisted deposition (IBAD) of an MgO layer through reflection high-energy electron diffraction (RHEED) pattern monitoring and analysis. The other is for composition control of a superconducting layer through surface color observation and control of metal source evaporation rates. By applying the above two methods, we achieved in-plane texture of about 4.8 ° in the MgO layer, as measured by FWHM of phi-scan of (220) peak, and the critical current of 750 A/12 mm width in the GdBCO layer along the length of more than 650 m, with excellent uniformity.

Study on stabilization and quench protection of coils wound of HTS coated conductors considering quench origins – Proposal of criteria for stabilization and quench protection

It has been considered that HTS coils are hard to be quenched because of high quench energy due to high critical temperature and high specific heat of HTS wires. Therefore, attention to quench protection was not much paid. However, HTS coils still have possibility to be quenched during operation by mainly the following two origins, (a) presence of non-recoverable local defects in the conductors and (b) temperature rise of long part of the conductor. Actually, severe quench accidents, such as burning coils, are occurring in various places as scales of HTS increased. Purposes of this paper are to study on behaviors of normal zone and hot spot temperature of wires during quench detect/energy dump sequence and to find criteria for the stability and quench protection. In the paper, criteria are proposed for stability and quench protection of HTS coils. A criterion for the stability is that a coil can be operated stably without a quench against defects in coil windings and that for quench protection is that a coil can be safely protected from damages caused by a quench due to temperature rise of long part of coil wires. The criteria are used as design rules for HTS coils.