• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.04a
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• pp.88-95
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• 2002

Recent development in the field of RE-Ba-Cu-O (REBCO, RE: Y or rare earth elements) bulk high-Tc superconductors (HTS) is reviewed in the present paper. After the fatal weak link problem of sintered REBCO superconductors has been overcome by melt processing, this field has been greatly advanced during last ten years. The critical current density $J_c$ at 77 K has been enhanced by introducing effective flux pinning sites into the $REBa_2Cu_3O_y$ (RE123) superconducting matrix. Large melt-textured REBCO bulk crystals have been fabricated with the TSMG(top-seeded melt growth) technique. Mechanical properties of REBCO bulks have been improved by using the Ag additive or epoxy resin. Real bulk applications such as current lead, fault current limiter, flywheel energy storage system, magnetic field source, magnetic separation system, and etc., surely come true near future.

• Proceedings of the KIEE Conference
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• 1997.07c
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• pp.794-796
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• 1997

The superconducting magnetic energy storage (SMES) system is considered to be useful to charge or release an energy in power system because of the high efficiency and quick response. But we need much capital to construct and to operate a SMES. A site and capacity of SMES are important elements for effective operating and planning. In this paper, we proposed a performance function to determine an optimal site and capacity of SMES according to variety condition of power system such as fault point. In addition, to demonstrate the validity of a proposed method, the simulations were carried out on two-machine 5-bus system.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.10a
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• pp.288-290
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• 2003

The transformer is expected to be an essential component of resistive type superconducting fault current limiter (SFCL) for both the increase of voltage ratings in SFCL and the simultaneous quench due to different critical current between HTSC elements. However, for the design to prevent the saturation of iron core and the effective fault current limitation, the analysis for operation of SFCL with consideration for the magnetization characteristics are required. In this paper, the fault current limiting characteristics related with the magnetization ones were investigated through the variation of the ratio of the number of turns in the 1st and the 2nd windings. The proper design condition with variation of the number of turns to make the effective fault current limiting operation could be determined.

• Structural Engineering and Mechanics
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• v.4 no.6
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• pp.613-630
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• 1996

The homogenization method is used to develop a beam element in space for thermo-mechanical analysis of unidirectional composites. Local stress and temperature field in the microscale are described using the function of homogenization. The global (macroscopic) behaviour of the structure is supposed to be that of a beam. Beam-type kinematical hypotheses (including independent shear rotations) are hence applied and superposed on the microdescription. A macroscopic stiffness matrix for such a beam element is then developed which contains the microscale properties of the single cell of periodicity. The presented model enables us to analyse without too much computational effort complicated composite structures such as e.g. toroidal coils of a fusion reactor. We need only a FE mesh sufficiently fine for a correct description of the local geometry of a single cell and a few of the newly developed elements for the description of the global behaviour. An unsmearing procedure gives the stress and temperature field in the different materials of a single cell.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.4
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• pp.700-704
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• 2011

This paper proposes a coordinative protection study results of 22.9kV HTS(High-Temperature Superconducting) cable implemented distribution system. HTS cable can provide about 5 times larger transfer capacability compare to conventional XLPE cable, however, it has different heat characteristic so called quench. This paper presents the simulation results on Ichun substation HTS cable which connects main transformer and 22.9kV bus. Various expected fault cases are considered and discussed to examine whether conventional protection scheme is effective to protect both of existing facilities and HTS cable. With the results of simulation, conventional protection scheme can be used if instantaneous element and time inverse elements could be adjusted with proper time coordination. Internal temperatures of HTS cable conductor in safe region with proper protection without quench. This results are to be demonstrated by the field test and will be implemented in Ichon substation HTS cable protection and control system.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.213-216
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• 1999

BSCCO thin films are fabricated via a co-deposition process by an ion beam sputtering with an ultra-low growth rate, and sticking coefficients of the respective elements are evaluated. The sticking coefficient of Bi element exhibits a characteristics temperature dependence : almost a constant value of 0.49 below 730$^{\circ}C$ and decreases linearly with temperature over 730$^{\circ}C$. This temperature dependence can be elucidated from the evaporation and sublimation rates of bismuth oxide, Bi$_2$O$_3$ from the film surface. It is considered that the liquid phase of the bismuth oxide plays an important role in the Bi(2212) phase formation in the co-deposition process.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.11a
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• pp.59-62
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• 2003

This study investigated the phase transformation of the $REBa_2Cu_3O_{7-x}$ (RE=Nd, Gd, By) superconductor, and CCT (Continuous-Cooling-Transformation) along with the TTT (Time-Temperature-Transformation) diagrams are suggested according to the isothermal and continuous cooling heat-treatments. According to result of fabricated single crystal of RE-123 superconductor through TSMG method based on phase transformation neted among heat treatment process, when the ionic radius elements was decreased, RE-211 phase was well-distributed. According to result that examine about seed of pretreatment effect of TSMG method, magnetic hysteresis improved when preprocess among oxygen atmosphere in same seed. and used after. Effect of miscut expressed good superconducting special quality in case miscut uses big seed.

• Progress in Superconductivity and Cryogenics
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• v.6 no.3
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• pp.50-55
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• 2004

We fabricated and tested a resistive type superconducting fault current limiter (SFCL) of three-phase 6.6 $kV_{rms}/200 A_{rms}$ rating based on YBCO thin films grown on sapphire substrates with a diameter of 4 inches, Short circuit tests were carried out at a accredited test facility for single line-to- ground faults, phase-to-phase faults and three-phase faults, Each phase of the SFCL was composed of 8${\times}$6 elements connected in series and parallel respectively. Each element was designed to have the rated voltage of 600 $V_{rms}$. A NiCr shunt resistor of 23 Ω was connected to each element for simultaneous quenches. Firstly, single phase-to-ground fault tests were carried out. The SFCL successfully developed the impedance in the circuit within 0.12 msec after fault and controlled the fault current of 10 $kA_{rms} below 816 A_{peak}$ at the first half cycle. In addition, in case of phase-to-phase fault and three- phase fault test. simultaneous quenches among the SFCLs of the phases successfully accomplished. In conclusion. the SFCL showed excellent performance of current limitation upon fault and stable operation regardless of the amplitude of fault currents.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.05a
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• pp.46-48
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• 2006

We investigated the analysis of operation mode of three-phase flux-lake type superconducting fault current limiter(SFCL). The structure of the integrated three-phase flux-lock type SFCL consisted of three-phase flux-lock reactor wound on an iron core with the same turn between coil 1 and coil 2 in each phase. When the SFCL is operated under the normal condition, the flux generated in the iron core is zero because the flux generated between two coils of each single phase is canceled out. Therefore, the SFCL's impedance is zero and the SFCL has negligible influence on the power system, However, if a fault occurs in any single-phase among three phases, the flux generated in the iron core is not zero any more. The flux makes elements of all phase-quench irrespective of the fault type, which reduces the current of fault phase as well as the current of sound phase.

• Progress in Superconductivity and Cryogenics
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• v.11 no.2
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• pp.7-10
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• 2009

Effects of $BaCO_3$ purity on the superconducting properties of top seeded melt growth (TSMG) processed $Y_{1+x}Ba_2Cu_3O_{7-y}$ (Y1+x, x=0.1 and 0.2) superconductors were investigated. $YBa_2Cu_3O_{7-y}$ (Y123) powder prepared using $BaCO_3$ with 99.75% purity and commercially available Y123 powder of 99.9% were used for the fabrication of single Y123 grain superconductors. $T_c$ values of the Y1+x samples prepared using low purity Y123 powder were slightly lower than those of the samples prepared using a high purity powder. In addition to the lower $T_c$, an anomalous peak effect in the intermediate magnetic fields was observed in Y1+x samples prepared using the low purity $BaCO_3$ powder. The slight decrease in $T_c$ and the anomalous peak effect are ascribed to the possible incorporation of a Y123 phase with impurity elements such as strontium and calcium included in the $BaCO_3$powder of 99.7%. The result suggests that the low purity $BaCO_3$ powder of a low price can be used as a raw power for the fabrication of single grain YBCO bulk superconductors.