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Jaeun Yoo,Sang Moo Lee,Ye Hyun Jung,Jaeyoung Lee,Dzung Nguyen Xuan,Dojun Youm,Hosup Kim,Hongsoo Ha,SangSoo Oh IEEE 2008 IEEE transactions on applied superconductivity Vol.18 No.2
<P>We developed a method for the estimation of AC loss in superconducting tapes. First we measured the field profiles, H(x, H<SUB>a</SUB>), near the surface of a coated conductor (CC) using the scanning Hall probe method. Here, the x axis was parallel to the in-plane transverse direction of the CC tape and H<SUB>a</SUB> is the external field applied in normal direction with respect to the tape surface. Then from H(x, H<SUB>a</SUB>), we calculated the current profiles, J(x, H<SUB>a</SUB>), by the inversion method. From J(x,H<SUB>a</SUB>) and the corresponding flux densities, we calculated the hysteretic energy losses per cycle, Q<SUB>M</SUB> ldr H<SUB>a</SUB> was decreased from H<SUB>peak</SUB> to -H<SUB>peak</SUB> stepwise, and the temperatures were 77 K and 72 K. We estimated Q<SUB>M</SUB> for various values of H<SUB>peak</SUB>. We calculated the dimensionless characteristic function, g, which are defined by Q<SUB>M</SUB>/(mu<SUB>0</SUB>I<SUB>c</SUB> <SUP>2</SUP>). Here I<SUB>c</SUB> is the critical current. Our g is similar to the Brandt's theoretical g although the current profile, J(x, H<SUB>a</SUB>), is somewhat different.</P>
Yoo, Jaeun,Lee, SangMoo,Jung, YeHyun,Kwak, Kisung,Rhee, Joonkyu,Youm, Dojun,Kim, Hosup,Ha, Hongsoo,Oh, SangSoo,Oh, Sangjun IOP Publishing Ltd 2009 Superconductor science & technology Vol.22 No.4
<P>The hysteresis loss in a Sm<SUB>1</SUB>Ba<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7−δ</SUB> coated conductor was estimated from magnetic field profiles measured by the scanning Hall probe method. Current, <I>I</I><SUB>a</SUB>, and magnetic field, <I>B</I><SUB>a</SUB>, were applied simultaneously; <I>B</I><SUB>a</SUB> was applied in the normal direction with respect to the tape surface. <I>B</I><SUB>a</SUB> and <I>I</I><SUB>a</SUB> were varied from <I>B</I><SUB>peak</SUB> to −<I>B</I><SUB>peak</SUB> and from <I>I</I><SUB>peak</SUB> to −<I>I</I><SUB>peak</SUB>, respectively, with the ratio α = <I>I</I><SUB>a</SUB>/<I>B</I><SUB>a</SUB> fixed during the variation. Three values of α were taken for the three load lines. The values of <I>B</I><SUB>peak</SUB>/<I>I</I><SUB>peak</SUB> were varied from 0 mT/0 A to 10.7 mT/116 A, 99.1 mT/50 A, and 298.2 mT/46.1 A, respectively, for the three load lines. From the measured values of magnetic field profiles, the current profiles were calculated by the iterative inversion method. From the current profiles, the flux density profiles and the hysteresis loss, <I>Q</I>, were then calculated for various values of <I>I</I><SUB>peak</SUB>(= α<I>B</I><SUB>peak</SUB>) in each load line. The results were compared with theoretical calculations based on Brandt’s model. When <I>B</I><SUB>peak</SUB> was about 300 mT, the estimated values of <I>Q</I> were several times smaller than the theoretical values of <I>Q</I> with the self-field <I>I</I><SUB>c0</SUB>. The low value of <I>Q</I> in this case is due to the field dependent <I>I</I><SUB>c</SUB> and the saturation effect of the current profiles, which results in significant reduction of the induced magnetic moment, <I>M</I>. </P>
Yoo, Jaeun,Han, Young-Hee,Kim, Hey-Rim,Park, Byung-Jun,Yang, Seong-Eun,Kim, Heesun,Yu, Seung-Duck,Park, Kijun The Korea Institute of Applied Superconductivity a 2014 한국초전도저온공학회논문지 Vol.16 No.2
In this study we investigated ac transport current losses in the face to face stack for the anti-parallel current flow, and compared the electromagnetic properties with those of the single SC tape as well as those of the same stack for the parallel current path. The gap between the SC tapes in the stack varied in order to verify the electromagnetic influence of the neighbors when current flows in opposite direction, and the model was implemented in the finite element method program by the commercial software, COMSOL Multiphysics 4.2a. Conclusively speaking, the loss was remarkably decreased for the anti-parallel current case, which is attributed the magnetic flux compensation between the SC layers due to the opposite direction of the current flows. As the gap between SC tapes was increased, the loss mitigation became less effective. Besides, the current density distribution is very flat cross the sample width for the narrower gap case, which is believed to be benefit for the power electric system. These results are all in good agreement with those predicted theoretically for an infinite bifilar stack.
Scanning Hall probe measurements of field distributions of a coated conductor under applied fields
Yoo, Jaeun,Jung, Yonghwan,Lee, Jaeyoung,Lim, Sunme,Lee, SangMoo,Jung, YeHyun,Youm, Dojun,Kim, Hosup,Ha, HongSoo,Oh, Sangsoo IOP Publishing Ltd 2006 Superconductor science & technology Vol.19 No.12
<P>We measured the field profiles near the surface of a coated conductor (CC) under various applied fields by using the scanning Hall probe method. The field, applied in the normal direction, was increased from zero to 171.5 Oe and then decreased to −58.8 Oe. We could not analyse our data completely by the direct use of Brandt’s calculation but by a modification with unusual field dependences of the introduced parameters. Since Brandt’s original calculation was based on homogeneous films, it was not suitable for CCs with coarse granular structures. The modified calculations with appropriate parameters are related to the coarse granular structures. Those parameters, <I>D</I>, <I>J</I><SUB>c</SUB>, and <I>R</I>, represent the three characteristics of the flux penetration network: the average distance of flux penetrations, the density of critical sheet currents, and the range of meandering of the flux penetration front, respectively. The external field dependences of these parameters were different from those of the classical critical state model. </P>
Design of Post Metal Shields Through Electric Field Distribution Analysis for a 154-kV SFCL
Yoo, Jaeun,Shin, Woo-Ju,Han, Young-Hee,Lee, BangWook,Kim, Hey-Rim,Yang, Seong Eun,Kim, Heesun,Yu, Seung-Duck,Park, Kijun Institute of Electrical and Electronics Engineers 2015 IEEE transactions on applied superconductivity Vol.25 No.3
<P>Korea Electric Power Corporation has developed a 154-kV superconducting fault current limiter (SFCL). This report is a part of the design process of the SFCL, particularly for fixation of posts supporting the superconducting element on the cryostat wall side. For supporting the superconducting element, the use of a post insulator is inevitable; however, the post insulator and cryostat with liquid nitrogen <inline-formula> <TEX-math notation='LaTeX'><TEX>$(\mbox{L}\mbox{-}\mbox{N}_{2} ) $</TEX></tex-math></inline-formula> during operation of the SFCL form three junction points where electric field is intensified. In this study, we aim to design the metal shield in order to relax the electric field intensity at triple points (TPs through numerical analysis of electric field distribution. For the electric field distribution analysis, a commercial software based on the finite-element method was employed. Each design for the metal shield was checked whether it makes the electric field intensity at the TP sufficiently lower than dielectric strength in <inline-formula> <TEX-math notation='LaTeX'><TEX>$\mbox{L}\mbox{-}\mbox{N}_{2} $</TEX></tex-math></inline-formula> for 750-kV input and whether there is any electrically weak point on the metal. The designs of the metal shields were improved through four critical steps where thermal contraction, manufacture tolerance, and insulation distance in <inline-formula> <TEX-math notation='LaTeX'><TEX>$\mbox{L}\mbox{-}\mbox{N}_{2} $</TEX></tex-math></inline-formula> were considered. It was experimentally verified that there was no electric breakdown in <inline-formula> <TEX-math notation='LaTeX'><TEX>$\mbox{L}\mbox{-}\mbox{N}_{2} $</TEX></tex-math></inline-formula> between the metal shield and the fiber-reinforced plastic post insulator for the lightning impulse test and the ac breakdown voltage test according to the IEC 60137 standard.</P>
액티블리: 메타버스 기반 소셜 웰니스 어플리케이션의 효과성 검증
김자은(Jaeun Kim),김지은(Jieun Kim),최현지(Hyounji Choi),장진규(Jinkyu Jang),신재찬(Jae Chan Shin),조아라(Ara Cho),유영재(Youngjae Yoo) 한국HCI학회 2023 한국HCI학회 학술대회 Vol.2023 No.2
코로나 19 는 사람들의 신체 건강과 소셜 활동에 부정적 영향을 주고 있다. 소셜 웰니스로 설명되는 이러한 건강에 관한 문제를 해소하기 위해 디지털 헬스케어 서비스에 대한 사람들의 관심이 높아지고 있다. 본 연구에서는 메타버스 기술을 활용해 게임 요소를 적용한 동기 부여 환경을 제공함으로서 소셜 웰니스를 증진시킬 수 있는 모바일 어플리케이션 ‘액티블리’를 개발하고, 그 효과에 대해 알아보고자 한다. 이를 위해, 준실험 방식의 실험 설계를 바탕으로 필드 스터디를 진행하고 정량적, 정성적 데이터를 수집해 검증하였다. 액티블리 어플리케이션을 2 주간 사용하도록 한 후 신체 활동량, 수면 시간, 사회적 연결감을 매일 측정했다. 실험 참여자 모집시 측정된 참여자의 직전 일주일간의 데이터와 어플리케이션 사용 후 데이터를 수집해 그 두 개의 그룹 간 평균비교를 진행하였다. 연구 결과, 액티블리 어플리케이션 사용으로 소셜 웰니스 지표 중 신체 활동량과 사회적 연결감이 증가하는 것으로 나타났다. 또한, 사용자의 지속 사용을 유도하기 위해 사용성 측면의 개선과 동기부여 측면의 추가 기능 디자인이 필요함을 확인하였다.