• Progress in Superconductivity and Cryogenics
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• v.22 no.2
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• pp.38-43
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• 2020

This paper presents comparative research on characteristics of air-cored and iron-cored high-temperature superconductor (HTS) field winding synchronous motors. The 100 kW air-cored model is designed analytically by Spatial Harmonic Method, and based on this model, the iron-cored model having the same output power is designed for comparison. Due to the substantial difference of permeability property between air and iron-core, there is a difference of magnetic field magnitude and angle with respect to the HTS tape c-axis, resulting in a different critical current of the field winding considering the anisotropic property of HTS tape. For a detailed comparison between two models, the following key motor characteristics are calculated through the Finite Element Method (FEM) simulation: 1) critical current; 2) HTS wire length; and 3) torque characteristics. From the simulation results, it can be confirmed that the critical current value of the iron-cored model increases by 33 %. Also, in the case of the superconducting wire consumption, those of the iron-cored and air-cored models are 95.3 m and 815.6 m, respectively. So the wire usage can be reduced to about 88 % by using iron core. However, in terms of torque characteristics, the torque ripple of the iron-cored model is about twice as large as that of the air-cored model, which may be a disadvantage on vibration and acoustic noise.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.1
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• pp.52-56
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• 2011

The ongoing Superconducting Fault Current Limiter(SFCL) development mainly has focused on the application of commercializaton and power system through combining with normal-conducting device, moving away from current-limiting method, which is solely dependant on the existing superconductor. Compared to the structural development above, on the other hand, the research on applying superconducting current-limiting element to SFCL, the heart of SFCL, still has a lot left to do, apart form traditional resistive type SFCL. In this study, we looked into the current limiting characteristic of SFCL using core and coil. YBCO coated conductor with stainless steel stabilizer layer was verified by the excellent of current-limiting element of the resistive type SFCL that has a high Jc and index as well as being superior in mechanical property. Also, we study temperature characteristics and resistance characteristics, max voltage, response time and current-limiting ability that can be an indicator as current-limiting element while applying to superconducting current-limiting element caused by variation of winding direction, winding ratio of SFCL using core and coil.

• Journal of the Korean Ceramic Society
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• v.35 no.2
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• pp.137-144
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• 1998

High-temperature superconducting joints between 61 filaments of Bi-2223 tapes were fabricated by chem-ical corrosion and repeated thermomechanical process. The silver sheath of the superconducting tape was chemically removed using chemical etchant(NH4OH:H2O2=1:1) from one side of each tape without altering the form of lap joint. The joined region was formed by uniaxial pressing and a series of thermomechanical process and then subjected to properties measurement and microstructural analysis. The critical current(Ic) variation and I-V characteristics along the joint were mesured with several configuration of proble points. Ic value of the transition region of the joint inthe multifilament tape which limit the total current carring capacity of the superconducting tape was higher than that of monofilament tape. But the transition ex-ponent n-value of the multi-filament tape was lower than that of monofilament wire due to the interaction of the individual superconducting core of the multi-filament. The critical current through the joint area was improved by respeated press and reaction annealing treatment.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.1120-1121
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• 2015

대용량 SMES(Superconducting Magnetic Energy Storage)를 제작하기 위해서는 높은 자장특성을 가고 있는 2세대 HTS(High-Temperature Superconductor) 선재를 사용하는 것이 효율적이다. SMES의 에너지밀도를 높이기 위해서는 선재에 많은 전류를 흘려야 하는데, 수직자기장이 커지면 임계전류가 작아지는 2세대 HTS 선재의 특성상 토로이드형태의 SMES가 유리하다. SMES를 설계하기 전에 선재의 사용량을 줄이고 체적을 줄이기 위해서 정확한 설계와 평가가 필요하다. 유한요소법을 사용한 상용프로그램을 이용하여 쉽게 해석할 수 있으나 토로이드 형태의 SMES는 대칭성의 문제로 3차원 해석을 해야만 한다. 그러나 2차원 해석에 비해 여러 가지 제약조건이 따르며 해석 시간이 많이 소요된다. 본 논문에서는 이러한 문제점을 해결하기 위해 분석적이고 통계적으로 고온 초전도 코일에서 작용하는 최대 수직자장을 결정하는데 이해하기 쉽고 효율적으로 계산하는 방법을 제시했다. 본 논문에서는 싱글펜케이크코일의 크기에 따른 최대 자장값을 계산하였고 싱글펜케이크코일이 토로이드형태로 배치된 토로이드 모델에서 주변코일이 싱글펜케이크코일의 미드포인트에 미치는 자장값을 계산하여 두 계산값을 합하는 방식으로 최대 자기장을 계산하였다. 이 방법은 현저한 시간단축과 효율적인 설계를 할 수 있는 새로운 계산 방법으로 기존 FEM을 사용해 걸리는 시간에 비해 1/1000정도의 시간단축을 할 수 있었다.

• Progress in Superconductivity and Cryogenics
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• v.19 no.3
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• pp.44-48
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• 2017

Current lead is a device that connects the power supply and superconducting magnets. High temperature superconductor (HTS) has lower thermal conductivity and higher current density than normal metal. For these reasons, the heat load can be reduced by replacing the normal metal of the current lead with the HTS. Conventional HTS current lead has same cross-sectional area in the axial direction. However, this is over-designed at the cold-end (4.2 K) in terms of current. The heat load can be reduced by reducing this part because the heat load is proportional to the cross-sectional area. Therefore, in this paper, heat load was calculated from the heat diffusion equation of HTS current leads with uniform and non-uniform cross-sectional areas. The cross-sectional area of the warm-end (65K) is designed considering burnout time when cooling system failure occurs. In cold-end, Joule heat and heat load due to current conduction occurs at the same time, so the cross-sectional area where the sum of the two heat is minimum is obtained. As a result of simulation, current leads for KSTAR TF coils with uniform and non-uniform cross-sectional areas were designed, and it was confirmed that the non-uniform cross-sectional areas could further reduce the heat load.

• Korean Journal of Crystallography
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• v.7 no.2
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• pp.147-155
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• 1996

Floating Zone Image furnace with halogen lamps as heat source has been made and applied to the growth of high-Tc superconductor Bi2Sr2CaCu2O8. The manufactured crystal growth equipment is composed of holder unit for setting the halogen lamps at the focal point of the elliptical mirror, image furnace with maximum temperature of 1800℃ with 1kW halogen lamps, cooling unit, feeding unit for supplying source material to the molten zone, pulling unit for crystal growth, and the control unit in the range of 2mm/hr -40 mm/hr vertical movement and 15rpm - 12rpm rotation. Bi2Sr2CaCu2O8 fibers have been grown with 300W halogen lamps and characterized with XRD, SEM and EDS. The growth condition was air atmosphere, growth speed 3∼4mm/hr, rotation speed of upper and lower part 20∼25 rpm. The fiber was composed of 20∼25 rpm matrix phase and secondary phases such as (Sr,Ca)CuO2 and (Sr,Ca)2CuO3.

• Journal of the Korean Ceramic Society
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• v.43 no.11 s.294
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• pp.715-723
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• 2006

Perovskite oxide materials are very important for the electronics industry, because they exhibit promising properties. With an interest in the obvious applications, significant effort has been invested in the growth of highly crystalline epitaxial perovskite oxide thin films in our laboratory. And the desired structure of films was formed to achieve excellent properties. $Y_1Ba_2Cu_3O_{7-x}$ (YBCO) superconducting thin films were simultaneously deposited on both sides of 3 inch wafer by inverted cylindrical sputtering. Values of microwave surface resistance R$_2$ (75 K, 145 GHz, 0 T) smaller than 100 m$\Omega$ were reached over the whole area of YBCO thin films by pre-seeded a self-template layer. For implementation of voltage tunable high-quality varactor, A tri-layer structured SrTiO$_3$ (STO) thin films with different tetragonal distortion degree was prepared in order to simultaneously achieve a large relative capacitance change and a small dielectric loss. Highly a-axis textured $Ba_{0.65}Sr_{0.35}TiO_3$ (BST65/35) thin films was grown on Pt/Ti/SiO$_2$/Si substrate for monolithic bolometers by introducing $Ba_{0.65}Sr_{0.35}RuO_3$ (BSR65/35) thin films as buffer layer. With the buffer layer, the leakage current density of BST65/35 thin films were greatly reduced, and the pyroelectric coefficient of $7.6\times10_{-7}$ C $cm^{-2}$ $K^{-1}$ was achieved at 6 V/$\mu$m bias and room temperature.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.9B
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• pp.1668-1675
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• 1999

In this thesis, a narrowband bandpass filter using HTS is proposed for the multiplexer of the satellite communication subsystems. The proposed structure using HTS provides the narrower band and the lower insertion loss characteristics than the conventional parallel-coupled-line bandpass filter. The filter structure using hairpin-line only cause the spurious modes due to the surface waves. But these modes can be lessened by using the hybrid hairpin-line/parallel-coupled-line proposed in this thesis. The narrowband bandpass filters using HTS at the operation frequency of 14.25 GHz are fabricated to have the narrow bandwidth less 1% and the insertion loss less 3dB in comparison with the normal metal microstrip filter with the same three poles. The experimental results show that the filter using HTS has the characteristics of the narrower bandwidth and less insertion loss and can be fabricated with more compact size in comparison with the bandpass filter using normal metal.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.243-244
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• 2006

As an preliminary study for the quench protection of high temperature superconducting (HTS) cable using superconducting fault current limiter (SFCL), experimental research was carried out. The test circuit was composed of Bi-2223/Ag HTS tape and a SFCL made of YBCO thin films. In the normal state, the applied current of 56 A, which was critical current of HTS tape, could be flown through the circuit without resistive loss. Increasing the currents, the quench development of both materials was investigated from the voltage signal acquired from the resistance of the quenched superconductor. Up to around 10 times of the critical current was applied to the HTS tape and the current limiting characteristics of SFCL were investigated. In addition, for the finding out the optimal operating condition of SFCL such as the numbers of elements, a shunt resistor was applied to the SFCL and quench characteristics were analyzed as well.

• Progress in Superconductivity and Cryogenics
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• v.21 no.1
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• pp.31-35
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• 2019

The lumped-parameter circuit model for a no- insulation (NI) high temperature superconductor (HTS) magnet has been well understood after many experimental and analytic studies over a decade. It successfully explains the non-linear charging behaviors of NI magnets. Yet, recently, multiple groups reported that the post-quench electromechanical behaviors of an NI HTS magnet may not be well explained by the lumped circuit model. The characteristic resistance of an NI magnet is one of the key parameters to characterize the so-called "NI behaviors" of an NI magnet and recently a few groups reported a potential that the characteristic resistance of an NI magnet may substantially vary during a quench. This paper deals with this issue, the increment of contact resistance of the no-insulation (NI) REBCO magnet during a quench and its impact on the post-quench behaviors. A 7 T 78 mm NI REBCO magnet that was previously built by the MIT Francis Bitter Magnet Laboratory was chosen for our simulation to investigate the increment of contact resistance to better duplicate the post-quench coil voltages in the simulation. The simulation results showed that using the contact resistance value measured in the liquid nitrogen test, the magnitude of the current through the coil must be much greater than the critical current. This indicates that the value of the contact resistance should increase sharply after the quench occurs, depending on the lumped circuit model.