• Progress in Superconductivity and Cryogenics
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• v.11 no.3
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• pp.10-14
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• 2009

Since a stabilizer of YBCO coated conductor (CC) plays a very important role of bypassing over-current and transferring heat generated in the moment of fault, it is one of big issues to determine the material of the stabilizer and its dimension for the high performance of the HTS power application system. Especially, in the case of a superconducting fault current limiter (SFCL), which requires it to react immediately to the occurrence of fault, characteristics of stabilizer are decisive in limiting fault current and recovering superconducting properties during and after quenching. In this paper, the quench / recovery characteristics of YBCO CCs with various thickness of stabilizer were analyzed. The quench/recovery test carried out at 20 $V_{rms}$, 5 cycles (60 Hz) and results showed that as the thickness of the stabilizer decreased, both the final approach temperature and the recovery time decreased.

• Progress in Superconductivity and Cryogenics
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• v.13 no.4
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• pp.1-4
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• 2011

From the viewpoint of high field application, the mechanical and critical current properties of recently developed $REBa_2Cu_3O_y$ (RE123, RE: rare-earth) coated conductors are summarized. In addition, effective flux pinning mechanisms in RE123 are also introduced. As one of the examples for high field application, the upgrading of the 18 T cryogen-free superconducting magnet is shown. The large anisotropy of $J_c$ is a problem at low temperature and high magnetic field. The nanorod is considered as the useful methods to improve the anisotropy of $J_c$, although its efficiency becomes small at low temperature.

• Progress in Superconductivity and Cryogenics
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• v.8 no.4
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• pp.15-18
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• 2006

REBCO coated conductors (RE: rare earth elements) have recently drawn great attention since they are known to possess stronger flux pinning centers in high magnetic fields compared with YBCO coated conductors. In this study, $GdBa_2Cu_3O_{7-d}(GdBCO)$ was selected to investigate the influence of the distance between target and substrate and substrate temperature on the superconducting properties of GdBCO films on the $SrTiO_3(100)$ substrate. Samples were fabricated by pulsed laser deposition (PLD) with a Nd:YAG laser (355nm). Under a given oxygen pressure of 800mTorr, we changed the distance between target and substrate from 5.5cm to 7.0cm and the substrate temperature from $750^{\circ}C\;to\;850^{\circ}C$. The crystallinity and texture of GdBCO films were analyzed by X-ray diffraction (XRD), and the surface morphology was observed by the scanning electron microscopy (SEM). Tc and Jc values were measured by the four point probe method. High quality GdBCO films with Tc of 89.7K and Jc over $1MA/cm^2$ at 77 K in self field were successfully fabricated by optimizing processing parameters. The detailed processing conditions, microstructure and superconducting properties will be presented for a discussion.

• Progress in Superconductivity and Cryogenics
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• v.12 no.1
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• pp.17-21
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• 2010

In the case of designing superconducting power apparatuses using the second generation high temperature superconducting wire, it is necessary to have a tape-splicing technique to achieve low splice resistance between coated conductor (CC) tapes. In this paper, an experimental splice method between YBCO CC tapes is proposed for a coil application. Splices were performed with a 37Pb-63Sn solder. YBCO samples were fabricated with various pressures and cooling rates. Joint resistances of the spliced samples of jointed YBCO CC tapes were measured and evaluated from V-I curves. In addition, optical micrographs were obtained to analyze the cross sectional microstructure of jointed samples.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.2
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• pp.282-288
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• 2007

Magnetization loss of high temperature superconductoring BSCCO tape and YBCO coated conductor(YBCOCC) is most important issue in the development of superconducting power devices. In this paper, the measured results of magnetization losses under various angles of external magnetic field in BSCCO tape stacked conductors and YBCO CC stacked conductors are presented and compared with each other. Also, we present the compared results of magnetization losses measured at arbitrary reaction magnetic fields and analyzed with perpendicular magnetic field components of those. The results show that magnetization losses of YBCO CC single and stacked conductors agree well with the analyzed value by it's perpendicular magnetic field component, but BSCCO single and stacked conductors are not.

• Progress in Superconductivity and Cryogenics
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• v.9 no.4
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• pp.1-6
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• 2007

We describe methods for depositing high temperature superconducting films on textured metal tapes by reactive co-evaporation (RCE). We discuss how RCE can be used to deposit on moving tape in a continuous fashion in a Garching-style process. Results are presented on films deposited by RCE at Los Alamos on IBAD-MgO textured tapes. The performance achieved, attaining over 500A/cm-width in self-field at 75.5 K, is competitive with the best results obtained by other processes for coated conductors. Tape production throughput is critical for the economics of the process and high deposition rates achieved in RCE are attractive for this. We present a detailed cost analysis model for HTS deposition using an RCE Garching process. The results indicate that HTS deposition can cost $<$5/kA{\cdot}m$ in a scaled up manufacturing environment.

• Progress in Superconductivity and Cryogenics
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• v.16 no.4
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• pp.7-16
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• 2014

Rare-earth barium copper oxide (REBCO) coated conductor (CC) tapes have already been commercialized but still possess some issues in terms of manufacturing cost, anisotropic in-field performance, $I_c$ response to mechanical loads such as delamination, homogeneity of current transport property, and production length. Development on improving its performance properties to meet the needs in practical device applications is underway and simplification of the tape's architecture and manufacturing process are also being considered to enhance the performance-cost ratio. As compared to low temperature superconductors (LTS), high temperature superconductor (HTS) REBCO CC tapes provide a much wider range of operating temperature and a higher critical current density at 4.2 K making it more attractive in magnet and coil applications. The superior properties of the REBCO CC tapes under magnetic field have led to the development of superconducting magnets capable of producing field way above 23.5 T. In order to achieve its optimum performance, the electromechanical properties under different deformation modes and magnetic field should be evaluated for practical device design. This paper gives an overview of the effects of mechanical stress/strain on $I_c$ in HTS CC tapes due to uniaxial tension, bending deformation, transverse load, and including the electrical performance of a CC tape joint which were performed by our group at ANU in the last decade.

• Progress in Superconductivity and Cryogenics
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• v.18 no.2
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• pp.1-4
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• 2016

To observe the superconducting current and structural properties of high critical temperature ($T_c$) superconductors (HTS), we suggest the following imaging methods: Room temperature imaging (RTI) through thermal heating, low-temperature bolometric microscopy (LTBM) and Raman scattering imaging. RTI and LTBM images visualize thermal-electric voltages as different thermal gradients at room temperature (RT) and superconducting current dissipation at near-$T_c$, respectively. Using RTI, we can obtain structural information about the surface uniformity and positions of impurities. LTBM images show the flux flow in two dimensions as a function of the local critical currents. Raman imaging is transformed from Raman survey spectra in particular areas, and the Raman vibration modes can be combined. Raman imaging can quantify the vibration modes of the areas. Therefore, we demonstrate the spatial transport properties of superconducting materials by combining the results. In addition, this enables visualization of the effect of current flow on the distribution of impurities in a uniform superconducting crystalline material. These imaging methods facilitate direct examination of the local properties of superconducting materials and wires.

• Progress in Superconductivity and Cryogenics
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• v.13 no.2
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• pp.5-8
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• 2011

This paper shows results of a design work of a program that is to develop a large power single phase high temperature superconducting (HTS) transformer. The program forms a part of a national project in Korea. A target of the design work is an HTS power transformer with rated voltages of 154 kV/22.9 kV and material for windings is supposed to be coated conductor. The design results presents in this paper will include: 1)HTS winding structures for high voltage in liquid nitrogen, 2)design result of continuously transposed coated conductor (CTCC), 3)conceptual design of high voltage bushings, 4)cooling system. A feasibility study will succeed to this design work for construction of a prototype HTS power transformer with capacity/voltage of 33 MVA/154 kV.

• Progress in Superconductivity and Cryogenics
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• v.25 no.4
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• pp.50-53
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• 2023

In this study, the photolithography process was chosen to reduce the aspect ratio of the cross-section of a high-temperature superconducting (HTS) tape by dividing the superconducting layer of the tape. Reducing the aspect ratio decreases the magnetization losses in the second-generation HTS tapes generated by AC magnetic fields. The HTS tape used in the experiment has a thin silver (Ag) layer of about 2 ㎛ on top of the REBCO superconducting layer and no additional stabilizer layer. A dry film resist (DFR) was laminated on top of the HTS tape by a lamination method for the segmentation. Exposure to a 395 nm UV lamp on a patterned mask cures the DFR. Dipping with a 1% Na₂CO₃ solution was followed to develop the uncured film side and to obtain the required pattern. The silver and superconducting layers of the REBCO films were cleaned with an acid solution after the etching. Finally, the segmented HTS tape was completed by stripping the DFR film with acetone.