• Progress in Superconductivity and Cryogenics
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• v.4 no.2
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• pp.5-10
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• 2002

Deposition condition of NiO that is one of Possible buffer layers for YBCO coated conductors was studied. NiO was deposited on textured Ni substrates by a MOCVD (metal-organic chemical vapor deposition) method. The degree of texture, and the surface roughness were analyzed by X-ray Pole figure, atomic force microscope and scanning electron microscope. The (111) and (200) textures were competitively developed , depending on an oxygen partial Pressure(PO2) and deposition temperature (Tp). The (200) textured NiO layer was deposited at Tp=450~47$0^{\circ}C$ and PO2= 1.67 Torr Out-of-Plane ($\omega$-scan) and in-plane ($\Phi$-scan) textures of the (200) NiO films were as good as 10.34$^{\circ}$ and 10.00$^{\circ}$ respectively The AFM surface roughness of NiO was in the range of 3~4.5 nm at PO2=0.91~3.34 Torr and at Tp=47$0^{\circ}C$ , and in the range of 3~13 nm at TP=450~53$0^{\circ}C$ and at PO2=1.67 Torr.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.52 no.7
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• pp.327-334
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• 2003

We have investigated the quench behavior of the series connection of resistive type superconducting fault current limiter (SFCL) components based on YBCO films. Equal shunt resistors $R_s$ across individual SFCL components successfully produced simultaneous Quenches for 5 components in series, resulting in equal application of voltage to all components. If the two components having the highest and the lowest critical currents ($I_c$) quench safely, others quench altogether The highest shunt resistance is to guarantee the safe quenches of all components, leading to the equal voltage applications within the first half cycle after a fault in the short circuit test. The highest $R_s$ was found to be 28 ［$\Omega$］ for the components in the given quench environment. Considering the safe quenches and protection coordination, the optimal $R_s$ was suggested to be approximately a half of the highest $R_s$,, allowing wide selection of $R_s$ and $I_c$'s. This design provides a practical wav of connecting small SFCL components in series for high voltage application.

• Proceedings of the KIEE Conference
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• 2000.07b
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• pp.663-665
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• 2000

We fabricated resistive superconducting fault current limiters (SFCL) based on YBCO thin films grown on 2-inch diameter saphire substrates Two SFCLs with nearly identical properties were connected in series to investigate the simultaneous quench. There was a slight difference in the rate of voltage increase between two SFCL units when they were operated independently. This difference. however, resulted in significantly unbalanced power dissipation between the units. This imbalance was removed by connecting a shunt resistor to an SFCL in parallel. The appropriate values of the shunt resistances were $80{\Omega}$ at $75 V_{rms}$. $100{\Omega}$ at $100 V_{rms}$ and $110{\Omega}$ at $120 V_{rms}$, respectively. Increased power input at high voltages also reduced the initial imbalance in power dissipation. but with increase in film temperature to higher than 200 K.

• Progress in Superconductivity and Cryogenics
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• v.21 no.4
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• pp.48-52
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• 2019

Recently, many studies have been reported on the magnetoresistance and Hall effect of REBCO thin films and bulk. The voltage interferes quench detection of high-temperature superconducting magnet and generates leakage current in no insulation high-temperature superconducting coil. Therefore, in this paper, experiments on magnetoresistance and Hall effect of commercial YBCO and GdBCO tapes have been carried out. As a result, anomalous voltages expected for the magnetoresistance and Hall effect of REBCO tapes were observed and analyzed. In addition, the voltage characteristics of REBCO have been identified, and the Hall coefficient are calculated for use in high magnetic field magnet applications.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05c
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• pp.19-22
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• 2003

For use in constructing highly sensitive thermal detectors, the present authors have been studying the preparation of Superconducting Flux Flow Sensor(SFFS). In this research, SFFS with five channel ($5{\mu}m$/1channel) has been fabricated based on the flux flow using high temperature superconducting thin films by the ICP etching technique. We have designed a bolometer based on the temperature dependence of the kinetic inductance of a superconducting flux flow thin film. In this paper examines the fabrications and flux flow resistance and thermometer responses of the highly sensitive sensor constructed of a thin YBCO film. It is also suggested that they will be applicable to a new type of flux flow sensor.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2003.11a
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• pp.279-281
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• 2003

We analysed the operating properties of resistive type superconducting fault current limiters (SFCLs) based on YBCO thin films with a single line-to-ground fault. When a single line-to-ground fault occurred, the short circuit current of a fault phase increased up to about 6 times of transport currents immediately after the fault instant and was effectively limited to the designed current level within 2 ms by the resistance development of the SFCL. The fault currents of the sound phases almost did not change because of their direct grounding system. The unsymmetrical rates of a fault phase were distributed from 6.4 to 1.4. It was found that the unsymmetrical rates of currents were noticeably improved within one cycle after the fault instant. We calculated the zero phase currents for a single line-to-ground fault using the symmetrical component analysis. The positive sequence resistance was reduced remarkably right after the fault but eventually approached the balanced positive resistance component prior to the system fault. This means that the system reaches almost the three-phase symmetrical state in about 60 ㎳ after the fault. The ground currents were almost 3 times of the zero phase mts since most of the fault currents flowed through the grounding line.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07a
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• pp.559-562
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• 2004

The $high-T_c$ Superconducting(HTS) antenna which consists of "H" type resonator has the benefits for the miniaturization of antenna in comparison with the microstrip antenna of the similar dimension. To fabricate the "H" type antenna HTS $YBa_2Cu_3O_{7-x}$(YBCO) thin films were deposited on MgO substrates using rf-magnetron sputtering. Standard etching processes were performed for the patterning of the "H" type antenna. For comparison between normal conducting antennas and superconducting antennas, the gold antennas with the same dimension were also fabricated. An aperture coupling was used for impedance matching between $50\Omega$ feed line and HTS radiating patch. The diverse experimental results were reported in terms of the resonant frequency, the return loss and the characteristics impedance. The "H" type superconducting antenna showed the performance of 1.36 in SWR, 24 % in efficiency, and 14.6 dB in the return loss superior to the normal conducting counterpart.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.296-297
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• 2005

We have investigated the quench performance of shunt reactors in the parallel connection of resistive type superconducting fault current limiter (SFCL) components based on YBCO films. To increase voltage rating, components are connected in series and to increase current level, they are connected in parallel. This method has cauesd the unbalanced quench between each components. To improve the problem, we have compared the quench properties between the current limiting components without and with shunt reactors connected in parallel. To improve the quench performance, across individual SFCL components connected the shunt reactor in parallel. The components with shunt reactors successfully produced simultaneous quench, resulting from the bypass of the fault current in the direction of the shunt reactor.

• Proceedings of the KIEE Conference
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• 2004.07c
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• pp.1745-1747
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• 2004

In order to anticipate gradual increase of fault current in electric power systems, current limiting technology and current limiting device has been investigated for a long time. But the commercial use of current limiting device was delayed due to the lack of effective method to insert impedance to the elective power systems without loss and surplus defects. However, novel current limiting device, which use superconducting materials, was considered as a dream technology to be applied in a distribution and transmission lines. LG Industrial systems and KERPI started to investigate resistive type superconducting fault current limiters in order to develop 154kV fault current limiters and this year, we succeed to test 3 phase 6.6kV/200A fault current limiters. Based on these achievements, 24kV superconducting fault current limiters will be realized withing 3 years which could be tested in a real fields. In this paper, the developments of fault current limiting module which use YBCO thin films, cryogenic systems, the structure and construction of 3 phase fault current limiters and finally the test results of 6.6kV superconducting fault current limiters will be introduced.

• Progress in Superconductivity and Cryogenics
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• v.16 no.2
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• pp.1-6
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• 2014

The five-year national project in Japan for R&D of coated conductors and applications, named as the Materials and Power Applications of Coated Conductors (M-PACC) project, was finished at the end of FY2013. The project consists of four sub-themes as cable, transformer, SMES and coated conductors. In the theme of coated conductors, the fabrication process had been developed to satisfy the requirements from the applications such as in-field $I_c$ performance, low AC loss in the long tapes etc. Through the project, the remarkable progress was achieved as follows; a high in-field minimum $I_c$ value over 54A/cm-width under 3T at 77K was realized in a 200m long EuBCO tape with artificial pinning centers of $BaHfO_3$ by the pulsed laser deposition (PLD) technique on the IBAD template. On the other hand, the AC loss reduction was confirmed in the tapes fabricated by both PLD and the metal organic deposition (MOD) techniques by scribing 100m tapes into 10-filamments. Additionally, the mechanism of the delamination phenomenon was systematically investigated and the strength was improved by eliminating the origins of the weak points in the films. Through the development, all targeted goals were accomplished and the several results were appreciated as a world champion data.