• Proceedings of the KIEE Conference
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• 1994.07a
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• pp.189-191
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• 1994

YBCO bulks for levitation have fabricated using MPMG method. The superconducting properties and repulsive/attractive force against permanent magnet were investigated for the specimens annealed at various periods after MPMG. A linear induction motor type levitation - traveling vehicle using the pinning force of MPMG processed YBCO bulk has fabricated. The floating or hanging small vehicle mounted with two YBCO pellets was confirmed to travel stabley on the Nd-Fe-B permanent magnet track. The traveling speed of the vehicle was confirmed to depend on AC frequency linearly. At 200 Hz, the travel ins speed was found to be 110 cm/sec.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.1
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• pp.20-25
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• 2011

This paper analyzed the application of Superconducting Fault Current Limiter (SFCL) on 22.9 [kV] bus tie in a power distribution system. Commonly, the parallel operations of power main transformers offer a lot of merits. However, when a fault occurs in the parallel operation of power main transformer, the fault currents might exceed the interruption capacity of existing protective devices. To resolve this problem, thus, the SFCL has been studied as the fascinating device. In case that, Particularly, the SFCL could be installed to parallel operation of various power main transformers in power distribution system of the Korea Electric Power Corporation (KEPCO) on 22.9 [kV] bus tie, the effect of the resistance of SFCL could reduce the increased fault currents and meet the interruption capacity of existing protective devices by them. Therefore, we analyzed the effect of application and proposed the proper impedance of the R-type SFCL on 22.9 [kV] bus tie in a power distribution system using PSCAD/EMTDC.

• Proceedings of the KIEE Conference
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• 1999.07a
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• pp.277-280
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• 1999

We fabricated a resistive superconducting fault current limiter of two stripe meander type based on a YBCO film, and performed current limitation experiments. In order to disperse the heat generated at hot spots in the YBCO film the film was coated with a gold shunt layer. At $0^{\circ}$ fault angle the minimum quench current was $9.6 A_{peak}$(meander line cross section: $5{\times}10^{-6}cm^2$) and the fast quench time was 0.63 msec. The resistance of the limiter continued to increase for three cycles due to heat generation in the gold layer and was stabilized afterwards. At $45^{\circ}$ and $90^{\circ}$ the fast quench time were 0.56 msec and 0.26 msec, respectively. The quench time is believed to be reduced because faults occurred when the current was increasing or was at the peak value. With the limiter we could effectively limit the fault current about 1/5 times right after the fault and about 1/8.5 times three cycles after.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.52 no.1
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• pp.23-26
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• 2003

This paper presents conceptual design and 3-D electromagnetic analysis of IMVA transformer with BSCCO-2223 High Tc Superconducting (HTS) tapes. The rated voltages of each sides of the transformer are 22.9 kV and 6.6 kV, and double pancake windings were adopted. High voltage and Low voltage sides were composed of several double pancake windings. Four HTS tapes were wound in parallel for the windings of low voltage side and were transposed in order to distribute the currents equally in each conductor The transformer core was designed as a shell type core made of laminated silicon steel plates and the core is separated with the windings by a cryostat with Fiberglass Reinforced Plastics(FRP). A sub-cooling system using L$N_2$ were designed to maintain the coolant temperature 65K. Finally perpendicular components of magnetic field applied to tapes were calculated 0.247 in the rated operation using 3-D analysis. A real 1MVA HTS transformer will be manufactured in near future based on the design parameters presented in this paper.

• Proceedings of the KIEE Conference
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• summer
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• pp.812-814
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• 2004

AC loss is one of the important parameters in (High Temperature Superconducting)HTS AC devices. Among the HTS AC power devices, the transformer is the essential part in the electrical power system. But unfortunately, the transformer is the worst HTS device concerning AC loss because of very large magnetization loss due to high magnetic field applied to the HTS wire. We calculated the magnetization losses in HTS pancake windings for transformer according to the operating temperature. Two kinds of arrangement of HTS pancake windings were adopted for calculation of AC losses of a shell type transformer, and the analysis results were presented and discussed.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.50 no.2
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• pp.65-72
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• 2001

This paper presents the design and test results of a 10kVA single phase HTS transformer which is operating at 77K. Double pancake windings with BSCCO -2223 HTS tape and GFRP cryostat with room temperature bore are used in the transformer. Four double pan cake windings were used in pancake windings are connected in parallel to conduct the secondary current of 45.4A. the rated voltages of each winding are 440/220V. Numerical calculation using Finite Element Method was used to evaluated the performance of each arrangement. Considering the magnetizing reactance, leakage reactance, electrical insulation and the circulating current in low voltage winding which had two windings in parallel, HLLH arrangement was finally chosen. Estimation of the AC loss, magnetizing loss and self field loss, in the design stage, where effects of perpendicular field and parallel field are considered. Room temperature bore type cryostat has been constructed and its heat loss was measured.

• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1719-1720
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• 2006

High temperature superconducting(HTS) power cable is expected to be used for power transmission lines supplying electric power for densely populated cities in the near future. Commercializing of HTS power cable is coming. Simulation is required for safety before install of HTS power cable, 3 fabrication model used at the power system simulation. In this paper, we shows a single line-to ground fault analysis in the grid system which has a loom length HTS power cable. The authors developed a single line-to-ground fault current calculation method which is considering the shield layer of HTS power cable. In the calculation, the T type equivalent circuit is used to derive the mutual inductance of the HTS power cable.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.2004-2005
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• 2007

고온 초전도체를 이용한 자속구속형 사고전류제한기는 1차권선과 2차권선을 감는 방향이나 감은 횟수의 비율에 따라서 부하전류용량과 전류제한용량이 다르다. 부하전류용량은 사고 발생 시 최초의 전류 제한 레벨과 밀접하게 관련이 되는데 자속구속형 사고전류제한기에서 최초의 전류 제한 레벨은 인덕턴스에 의해서 결정되기 때문이다. 전류제한용량은 사고전류제한기의 임피던스와 관계된다. 이 논문에서 자속구속형 사고전류제한기의 변압기 특성을 변화시키면서 부하전류용량과 전류제한용량의 변화를 살펴보았다.

• Bulletin of the Korean Chemical Society
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• v.11 no.6
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• pp.564-567
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• 1990

A lithiated compound $Li_{0.1}Pr^{3+}Ba_2Cu_3O_y$ has been successfully prepared by electrochemical method, which is achieved with a two electrode cell of the type: Metal(Li)/($Li^+\;,\;ClO_4^-$) + propylene carbonate/$PrBa_2Cu_3O_y$. All Pr ions in the lithiated compound are stabilized with a trivalent state as the other rare earths (Ⅲ) substituted in the 90K superconductor lattice ($Y_{1-x}Ln_x^-Ba_2Cu_3O_{7-{\delta}}$). Powder X-ray diffraction analysis shows that both compounds, $PrBa_2Cu_3O_y$ and $Li_{0.1}PrBa_2Cu_3O_y$ are isostructural with the 90 K superconductor, ($YBa_2Cu_3O_{7-{\delta}}$), nevertheless both of them are non-metallic and also non-superconducting down to 10 K. Magnetic susceptibility ${\chi}$ vs. temperature data indicate that Curie contribution from the magnetic ions (Pr and Cu) is weakened on the one hand, but on the other hand temperature-independent part of susceptibility ${\chi}_o$ increases depending upon the rate of lithium intercalation in $PrBa_2Cu_3O_y$ lattice.

• Progress in Superconductivity and Cryogenics
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• v.24 no.2
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• pp.1-6
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• 2022

This paper reviews the literature that has been published since 1980s related to cryogenic refrigeration systems for quantum computing. The reason why such a temperature level of 10-20 mK is necessary for quantum computing is that the superconducting qubit is sensitive to even very small thermal disturbances. The entanglement of the qubits may not be sustained due to thermal fluctuations and mechanical vibrations beyond their thresholds. This phenomenon is referred to as decoherence, and it causes an computation error in operation. For the stable operation of the quantum computer, a low-vibration cryogenic refrigeration system is imperative as an enabling technology. Conventional dilution refrigerators (DR), so called 'wet' DR, are precooled by liquid helium, but a more convenient and economical precooling method can be achieved by using a mechanical refrigerator instead of liquid cryogen. These 'dry' DRs typically equip pulse-tube refrigerators (PTR) for precooling the DRs around 4 K because of its particular advantage of low vibration characteristic. In this review paper, we have focused on the development status of 4 K PTRs and further potential development issues will be also discussed. A quiet 4 K refrigerator not only serves as an indispensable precooler of DR but also immediately enhances the characteristics of low noise amplifiers (LNA) or other cryo-electronics of various type quantum computers.