• 한국초전도학회:학술대회논문집
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• v.10
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• pp.241-247
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• 2000

77 K와 self-field에서 22 A 의 Ic 를 갖는 길이 120 m, 19-심 Bi-2223상 선재를 제조하여, 두 개의 double pancake 코일로 구성된 proto-type 고온초전도 자석을 설계, 제작하여 이 자석에서의 4.2 K와 77 K에서의 I-V 특성과 운전 특성을 평가한 결과, 이 자석은 77 K 등온조건에서는 9.5 A 의 Ic를, 77 K 헬륨가스 속에서는 8.3 A 의 Ic를 나타내었고, 4.2 K 등온조건에서는 93.7 A 의 Ic와 102 A 의 Iq를, 4.2K헬륨가스 속에서는 88.4A의 Ic 와 92.0 A 의 Iq를 나타내어, 이 자석은 4.2 K 와 77 K 의 등온조건에서 각각 0.58 T 와 0.06 T 의 자장을 발생하였는데, 이는 해석적 방법으로 계산한 결과와 잘 일치하였다. 그리고 이 자석이 전도냉각되어 4.2 K 에서 운전될 때의 안정성 특성평가로서, Ic 보다 약간 큰 전류인 89 A 를 인가한 결과, 전류인가 후 82.6초 후에 quench가 발생하였는데, 이 quench는 네 번째 pancake의 전류도입선부 연결부에서와 약간 늦지만 첫 번째 pancake의 전류도입선부 연결부에서 거의 동시에 개시되어 전체로 파급된 것으로 사료되었는데, Ic 가 낮은 첫번째 pancake에서 더 높은 전압 강하가 나타났다. 또한 장착된 heater를 통하여 77 K 에서 8.9 A 의 전류로 운전되고 있는 코일에 146 joule 의 열을 가했을 때 quench 가 일어났는데, 이때 quench 는 방위각 방향의 Bi-2223/Ag 선재를 따라서 보다 Kapton 절연층을 관통하는 선재의 반경방향으로 훨씬 빨리 전파하였다.

• Progress in Superconductivity and Cryogenics
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• v.17 no.1
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• pp.10-13
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• 2015

High-temperature superconducting coated conductors (HTS-CCs) are good candidates for resistive superconducting fault current limiter (RSFCL) applications. However, the high current density they can carry and their low thermal diffusivity expose them to the risk of thermal instability. In order to find the best compromise between stability and cost, it is important to study the heat transfer between HTS-CCs and the liquid nitrogen ($LN_2$) bath. This paper presents an experimental method to monitor in real-time the temperature of a quenched HTS-CC during a current pulse. The current and the associated voltage are measured, giving a precise knowledge of the amount of energy dissipated in the tape. These values are compared with an adiabatic numerical thermal model which takes into account heat capacity temperature dependence of the stabilizer and substrate. The result is a precise estimation of the heat transfer to the liquid nitrogen bath at each time step. Measurements were taken on a bare tape and have been repeated using increasing $Kapton^{(R)}$ insulation layers. The different heat exchange regimes can be clearly identified. This experimental method enables us to characterize the recooling process after a quench. Finally, suggestions are done to reduce the temperature increase of the tape, at a rated current and given limitation time, using different thermal insulation thicknesses.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.631-631
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• 2013

Battery has major drawbacks including its size and life expectancy, and environmental problem. As an alternative, energy harvesting is emerging as a potential solution to replace battery along with more energy-efficient IT devices. The idea of harnessing energy from our living environment is sustainable, semi-permanent, and eco-friendly. Also, unlike battery, energy harvester does not require much space to store energy. Therefore, energy harvesting can provide a better source of power for small, portable, and wireless devices. Among various ways of harvesting energy from our surroundings, triboelectricity is chosen due to its potential to be miniaturized, and efficient. Triboelectric effect occurs as two different materials with different polarity of charge separation come into contact through friction, and then become separated so that electric potential difference is achieved. In this research, such characteristic of triboelectricity is used as a way to convert ambient mechanical energy into electric energy.Series of recent researches have shown promising results that the triboelectric energy harvester can be simple and cost effective. However, sufficient electricity level required to operate mobile devices has not yet been achieved.In this research, our group focuses on the design and optimization of triboelectric energy harvesting device to enhance its output. By using maskless lithography to pattern Kapton film and silicon substrate, which is used as a mold for PDMS thin layer, and sputtering metal electrodes on each side, we fabricate and demonstrate different designs of triboelectric energy harvester that utilizes the contact electrification between a polymer thin film and a metal thin foil. In order to achieve optimized result, the output voltage and current are measured under diverse conditions, which include different surface structure and pattern, material, and the gap between layers.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.204-205
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• 2006

In the response to the demand for electrical energy, much effort aimed to develop and commercialize high temperature superconducting (HTS) power equipments has been made around the world. In Korea, companies and universities are developing a power distribution and transmission class HTS transformer that is one of the 21st century superconducting frontier projects. The composite winding of transmission class HTS transformer is concentrically arranged H1-L-H2 from center. H1 is continuous disk type, L is layer type and H3 is continuous disk type. For the development of transmission HTS transformer with composite winding, the cryogenic insulation technology should be established. We have been analyzed insulation composition and investigated electrical characteristics such as breakdown of $LN_2$, barrier, kapton films, surface flashover on FRP in $LN_2$. We are going to compare with measured each value and apply the value to most suitable insulating design of the HTS transformer.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.623-626
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• 2005

Toward the practical applications, on operation of conduction-cooled HTS SMES at temperatures well below 77 K should be investigated, in order to take advantage of a greater critical current density of HTS and considerably reduce the size and weight of the system. Recently, research and development concerning application of the conduction-cooled HTS SMES that is easily movement are actively progressing in Korea. Electrical insulation under cryogenic temperature is a key and an important element in the application of this apparatus. Using multi wrapped copper by polyimide film for HIS SMES, the breakdown characteristics of models for turn-to-turn, that is surface contact model, were investigated under ac and impulse voltage at 77 K. A material that is Polyimide film (Kapton) 0.025 mm thickness is used for multi wrapping of the electrode. Statistical analysis of the results using Weibull distribution to examine the wrapping number effects on breakdown voltage under ac and impulse voltage in $LN_2$ was carried.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.170-170
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• 2000

Synthetic polymers such as polyimide, polycarbonate, and poly(methyl methacrylate) are long chain molecules which consist of carbon, hydrogen, and heteroatom linked together chemically. Recently, polymer surface can be modified by using a high energy ion beam process. High energy ions are introduced into polymer structure with high velocity and provide a high degree of chemical bonding between molecular chains. In high energy beam process the modified polymers have the highly crosslinked three-dimensionally connected rigid network structure and they showed significant improvements in electrical conductivity, in hardness and in resistance to wear and chemicals. Polyimide films (Kapton, types HN) with thickness of 50~100${\mu}{\textrm}{m}$ were used for investigations. They were treated with two different surface modification techniques: Plasma Source Ion Implantation (PSII) and conventional Ion Implantation. Polyimide films were implanted with different ion species such as Ar+, N+, C+, He+, and O+ with dose from 1 x 1015 to 1 x 1017 ions/cm2. Ion energy was varied from 10keV to 60keV for PSII experiment. Polyimide samples were also implanted with 1 MeV hydrogen, oxygen, nitrogen ions with a dose of 1x1015ions/cm2. This work provides the possibility for inducing conductivity in polyimide films by ion beam bombardment in the keloelectronvolt to megaelectronvolt energy range. The electrical properties of implanted polyimide were determined by four-point probe measurement. Depending on ion energy, doses, and ion type, the surface resistivity of the film is reduced by several orders of magnitude. Ion bombarded layers were characterized by Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS), XPS, and SEM.

• Korean Journal of Materials Research
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• v.17 no.10
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• pp.509-515
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• 2007

In order to fabricate adhesiveless 2-layer flexible copper clad laminate (FCCL) used for COF (chip on film) with high peel strength, polyimide (PI; Kapton-EN, $38\;{\mu}m$) surface was modified by reactive $O_2^+$ and $N_2O^+$ ion beam irradiation. 300 mm-long linear electron-Hall drift ion source was used for ion irradiation with ion current density (J) higher than $0.5\;mA/cm^2$ and energy lower than 200 eV. By vacuum web coating process, PI surface was modified by linear ion source and then 10-20 nm thick Ni-Cr and 200 nm thick Cu film were in-situ sputtered as a tie layer and seed layer, respectively. Above this sputtered layer, another $8-9{\mu}m$ thick Cu layer was grown by electroplating and subsequently acid and base resistance and thermal stability were tested for examining the change of peel strength. Peel strength for the FCCLs treated by both $O_2^+$ and $N_2O^+$ ion irradiation showed similar magnitudes and increased as the thickness of tie layer increased. FCCL with Cu (200 nm)/Ni-Cr (20 nm)/PI structure irradiated with $N_2O^+$ at $1{\times}10^{16}/cm^2$ ion fluence was proved to have a strong peel strength of 0.73 kgf/cm for as-received and 0.34 kgf/cm after thermal test.