• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2002년도 High Temperature Superconductivity Vol.XII
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• pp.9-9
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• 2002

• Progress in Superconductivity
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• 제5권2호
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• pp.136-140
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• 2004

We fabricated and tested a resistive superconducting fault current limiters (SFCL) operated at 3.8 ㎸ based on YBCO thin films. The SFCL was composed of 7 components connected in series. Each component was designed to be capable of current limiting at 600 V, and has a SiC shunt resistor ( $R_{s}$) of 40 Ω in Parallel. Short circuit tests were carried out fur 0 and 90 degree faults lasting fur 5 cycles. The test results showed that the 7 components were quenched simultaneously under the safe quenches and evenly shared the applied voltage. The SFCL successfully suppressed the fault currents below 94 $A_{peak}$ within the quarter cycle after fault.t.t.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 B
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• pp.1219-1221
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• 2005

We improved quench properties of a superconducting fault current limiter(SFCL) components based on YBCO thin films. This consists of three components with nearly identical properties and one with slightly difference properties. The units were connected in series and first of parallel to increase the current and voltage ratings. It have caused significantly imbalanced power distribution. The imbalance remarkably improved by connecting a shunt reactor to the SFCL component in parallel.

• 한국결정학회지
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• 제14권2호
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• pp.51-55
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• 2003

YBa₂CU₃O/sub 7-8/(YBCO) coated conductor의 완충층 구조를 개선하기 위하여 2축배향된 Ni-3 wt%W 합금 기판위에 단일 완충층으로 SrTiO₃(STO) 박막을 증착하였다. YBCO와 STO 박막은 펄스레이저 증착법으로 성장시켰다. STO 박막의 표면은 증착온도에 따라 다른 미세조직을 보여 주었고, XRD 분석에서는 STO와 YBCO 박막이 금속기판의 배향성을 가지면서 성장되었음을 알 수 있었다. 액체질소 온도에서 1.2 MA/㎠의 임계전류밀도와 86 K의 임계온도를 가지는 짧은 길이의 coated conductor를 STO 단일완충층을 이용하여 제조하였다.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
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• pp.87-90
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• 1999

We have studied the annealing effects of 570 (SrTiO$_3$) single crystal substrate and the I-V properties of step-edge junctions after Ar ion milling. YBa$_2Cu_3O_7$ (YBCO) thin films are fabricated on the substrates by using pulsed laser deposition (PLD) and photolithography. The surface of Ar ion milled substrate was characterized with atomic force microscope (AFM) and scanning electron microscope (SEM) images. After the substrate was damaged by milling, the critical current density of YBCO thin films deposited on the substrate was lowered. The annealing of the damaged substrate at about 1000 $^{\circ}C$ recovered the critical current density to that before the milling. Futhermore the annealing helped junction formation due to high quality film and increased the yield rate for the fabrication of high quality step-edge junction.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 A
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• pp.336-338
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• 2002

We improved quench properties of a superconducting fault current limiter (SFCL) based on YBCO thin films by their serial and parallel combinations. The SFCL consisted of 6 switching elements fabricated of 4 inch-diameter YBCO thin films. Simple serial connection resulted in imbalanced power dissipation between switching elements even at the quench current difference of 0.6A. On the other hand, $2{\times}2\;and\;3{\times}2$ stack combinations produced simultaneous quenches. The $3{\times}2$ stack combination showed better simultaneous quench behavior than the $2{\times}2$ stacks. This is suggested to be because the currents between switching elements in parallel connection of the $3{\times}2$ stacks were more effectively redistributed than the $2{\times}2$ stacks.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2000년도 High Temperature Superconductivity Vol.X
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• pp.146-150
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• 2000

Two methods have been investigated to fabricate good quality step-edge Josephson junctions on STO, MgO, and LAO single crystal substrates. One is the annealing of substrates at 1050$^{\circ}$C in 1 atmospheric oxygen after Ar-ion milling. The other is the cleaning of step-edge by using Ar ion milling. The step-edge is characterized with atomic force microscope (AFM) images. And YBCO thin films are deposited by using pulsed laser. The I-V properties of step-edge junctions are characterized. The yield rate of step-edge junction is increased by new fabrication methods.

• 전기학회논문지
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• 제56권12호
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• pp.2078-2083
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• 2007

We have analyzed operating characteristics of transformer-type superconducting fault current limiter (SFCL) according to the serial or parallel connections of secondary coils with $YBa_2Cu_3O_7$ (YBCO) thin films. The turn ratio between the primary and secondary coils was 63:21. Transformer-type SFCL using a transformer with secondary winding of serial or parallel coils could reduce the unbalanced quench caused by differences of the critical current density between YBCO thin films. We found that transformer-type SFCL having serial or parallel connections induced simultaneous quench between the superconducting units. The limiting current in the transformer-type SFCL with a parallel connection was lowered to 30 % compared to the SFCL with a serial connection. In the meantime, when the currents generated in the superconducting units were similar, the voltage value in the parallel connection was 60 % as low as that in the serial connection. However, the voltage generated in the primary winding was some higher. In conclusion, we found that transformer-type SFCL with parallel connection of secondary coils was more effective in fault current limiting characteristics and in the reduction of the consumption power for superconducting units compared to those of the transformer-type SFCL with serial connection of secondary coils.

• E2M - 전기 전자와 첨단 소재
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• 제8권1호
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• pp.6-12
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• 1995

High Tc superconducting YBa$_{2}$Cu$_{3}$$O_{7-x}$ thin films were prepared on various substrates by off-axis rf magnetron sputtering method to examine the substrate effects on the film structure and its R-T characteristics. The SEM analysis showed that the surface morphology of the grown YBa$_{2}$Cu$_{3}$O.sub 7-x/, film has different characteristic structure with different substrate used. The film on (100) SrTiO$_{3}$ substrate has critical current density of 3*10$^{5}$ A/cm$^{2}$ at 77K under zero magnetic field. The X-ray diffraction measurements revealed that the films on (100) SrTiO$_{3}$ substrate have mixed a-axis and c-axis normal to the substrate surface and the films on (100) MgO and ZrO$_{2}$/sapphire substrates have c-axis normal orientation to the substrate surface. However, YBa$_{2}$Cu$_{3}$$O_{7-x}$ films on (100) sapphire substrates showed no preferential orientation.ion.

• Progress in Superconductivity
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• 제11권1호
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• pp.47-51
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• 2009

For many large-scale applications of high-temperature superconducting materials, large critical current density ($J_c$) in high applied magnetic fields are required. A number of methods have been reported to introduce artificial pinning centers in $YBa_2Cu_3O_{7-{\delta}}$ films for enhancement of their $J_c$. We studied the microstructures and characteristic of $YBa_2Cu_3O_{7-{\delta}}$ films fabricated on $SrTiO_3$ (100) substrates with ZnO nanorods as pinning centers. Au catalyst nanoparticles were synthesized on STO substrates with self assembled monolayer to control the number of ZnO nanorods. The density of Au nanoparticles is approximately $240{\sim}260{\mu}m^{-2}$ with diameters of $41{\sim}49nm$. ZnO nanorods were grown on STO by hot-walled PLD with Au nanoparticles. Typical size of ZnO nanorod was around 179 nm in diameter and $2{\sim}6{\mu}m$ in length respectively. YBCO films deposited directly on STO substrates show the c-axis orientation, while YBCO films with ZnO nanorods exhibit any mixed phases without any typical crystal orientation.