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Voltage Applicable to $Au/YBa_2Cu3O_7$ Meander Lines
김혜림,임성우,유승덕,박충렬,양성은,김우석,현옥배,Kim, H.R.,Yim, S.W.,Yu, S.D.,Park, C.R.,Yang, S.E.,Kim, W.S.,Hyun, O.B. The Korean Superconductivity Society 2010 Progress in superconductivity Vol.12 No.1
We investigated the voltage applicable to $Au/YBa_2Cu3O_7$ (YBCO) meander lines. The meander line was fabricated by patterning Au/YBCO thin films grown on sapphire substrates by photolithography. It was subjected to simulated AC fault currents, and the resistance was measured and analyzed. The samples were immersed in liquid nitrogen during the experiment for effective cooling. The voltage applicable to the meander lines depended on the fault duration. Dependence was strong at short fault durations, and weak at long durations. When the voltage was plotted as a function of the fault duration on a log-log scale, data fell more or less on straight lines for all meander lines. In other words, the voltage applicable to Au/YBCO meander lines on sapphire substrates was inversely proportional to $t^b$, where t is the fault duration and b ranges from 0.4 to 0.5. The results were analyzed quantitatively with the concept of heat balance. Under adiabatic condition, the voltage is to be inversely proportional to $t^{0.5}$ for all samples. Less value of b for some samples is thought to be due to cooling of the samples by liquid nitrogen.
복합고체절연물의 극저온 절연성능 평가를 위한 임펄스 내전압시험
김우석,유승덕,현옥배,김혜림,임성우,양성은,김희선,Kim, W.S.,Ryu, S.D.,Hyun, O.B.,Kim, H.R.,Yim, S.W.,Yang, S.E.,Kim, H.S. 한국초전도학회 2011 Progress in superconductivity Vol.13 No.1
High voltage insulation in cryogenic environment is one of big issues for development of superconducting power application, such as superconducting fault current limiter, transformer, transmission cable, and so on. We had proposed a composite solid insulator composed of plastics and polymer insulation sheets for a use of high voltage superconducting power applications. It is well known that the G10 FRP keeps its mechanical strength at very low temperature and the PPLP is very good insulator adopted as insulations for superconducting transmission cables. The composition of these two materials will show very good electrical and mechanical properties adequate for the insulation components of superconducting power applications, such as bushing, insulation barrier, and even for a cryostat. Dielectric strengths of prepared samples were measured at the temperature of boiling point of liquid nitrogen at atmospheric pressure, which will be presented in this paper to show a usefulness of this technique.
김우석,박충렬,현옥배,김혜림,임성우,유승덕,양성은,Kim, W.S.,Park, C.R.,Hyun, O.B.,Kim, H.R.,Yim, S.W.,Yu, S.D.,Yang, S.E. 한국초전도학회 2010 Progress in superconductivity Vol.12 No.1
A double line commutation (DLC) type SFCL with first peak limiting function has been proposed for ideal fault current limiting operation. Very fast switching (commutation) without any arc or high voltage problems for any kind of switching device is needed for the first peak current limiting. We've tried to find suitable conditions for a successful switching of a Vacuum Interrupter (VI) with HTS elements as a Peak Current limiting Resistance (PCR).
Bi-2212/Cu-Ni 튜브로 제작한 초전도 한류소자의 단락사고시험 결과
오성용,임성우,유승덕,김혜림,현옥배,Oh, S.Y.,Yim, S.W.,Yu, S.D.,Kim, H.R.,Hyun, O.B. 한국초전도학회 2008 Progress in superconductivity Vol.10 No.1
For the development of superconducting fault current limiters (SFCLs), fault current limiting elements were fabricated out of Bi-2212 bulk tubes and tested. The SFCL elements consisted of tube shaped Bi-2212 bulks and metal shunts for the stabilizers. Firstly, the Bi-2212 bulk tubes were processed based on a design of monofilar coils in order to acquire large resistance and high voltage rating. 300 mm-long Bi-2212 tubes were designed to have the current path of 410 cm in length with 24 turns and 41 mm in diameter. The processed monofilar coil, as designed, had 300 A $I_c$ at 77 K. The fabricated superconducting monofilar coils were affixed to Cu-Ni alloy as that of stabilizers. The Cu-Ni alloys were processed to have the same shape of the superconducting monofilar coils. The Cu-Ni coil had resistivity of 32 ${\mu}{\Omega}$-cm at 77 K and 37 ${\mu}{\Omega}$-cm at 300 K. The metal shunts were attached to the outside of the Bi-2212 monofilar coil by a soldering technique. After the terminals made of copper were attached to both ends of the superconductor-metal shunt composite, the gap between the turns and the surface of the elements was filled with an epoxy and a dense mesh made of FRP in order to enhance the mechanical strength. The completed SFCL elements went through fault tests, and we confirmed that the voltage rating of 143 $V_{rms}$ (E =0.35 $V_{rms}$/cm) could be accomplished.
김혜림,임성우,오성용,현옥배,Kim, H.R.,Yim, S.W.,Oh, S.Y.,Hyun, O.B. 한국초전도학회 2008 Progress in superconductivity Vol.9 No.2
We investigated the size effect on quench development in $Au/YBa_2Cu_3O_7$ (YBCO) thin film meander lines on sapphire substrates. The meander lines were fabricated by patterning YBCO films coated with gold layers. The lines were subjected to simulated AC fault current, and immersed in liquid nitrogen during the experiment. After the initial rapid rise, the resistance increased moderately and then slowly. In 4 inch-diameter meander lines, the period during which the resistance increased moderately was considerably longer than in 2 inch-diameter line. Moderate increase of resistance was originated from quench propagation. The film temperature was about 180 K at the point when the propagation was completed. The rate of resistance increase after the quench completion was not affected by the film size.
Analysis on Recovery in Au/YBCO thin Film Meander Lines
김혜림,임성우,오성용,현옥배,Kim, H.R.,Yim, S.W.,Oh, S.Y.,Hyun, O.B. The Korean Superconductivity Society 2007 Progress in superconductivity Vol.9 No.1
We investigated recovery in $Au/YBa_2Cu_3O_7$ (YBCO) thin film meander lines on sapphire substrates. The meander lines were fabricated by patterning YBCO films coated with gold layers. The lines were subjected to simulated AC fault current and then small current was applied for recovery measurements. The samples were immersed in liquid nitrogen during the experiment. After the fault, the resistance decreased linearly, first slowly and then fast to zero. The initial slow decrease was due to the decrease of the meander line temperature, whereas the fast decrease was originated from the transition from the normal state to the superconducting state. The recovery speed depended on the size of samples, and was faster in the smaller samples during the whole period of recovery. The experimental results were analyzed quantitatively with the concept of heat transfer within the sample and to the surrounding liquid nitrogen. A heat balance equation was solved for the initial phase of recovery, and an expression for the time dependence of resistance was obtained. The result agreed with data well.
Quench Development in Coated Conductors
김혜림,박충렬,임성우,유승덕,오성용,현옥배,Kim, H.R.,Park, C.R.,Yim, S.W.,Yoo, S.D.,Oh, S.Y.,Hyun, O.B. The Korean Superconductivity Society 2009 Progress in superconductivity Vol.10 No.2
We measured and analyzed the quench development in coated conductor(CC) tapes. The CC was grown on hastelloy substrates and has an Ag protection layer. The tapes were subjected to simulated AC fault currents for quench development measurement. They were immersed in liquid nitrogen during the experiment. The quench resistance increased rapidly first, and the increase slowed down afterwards. It increased linearly with applied voltage at lower voltages, and depended less strongly on applied voltage at higher voltages. The resistance was compared with that of Au/YBCO films grown on sapphire substrates, and found to increase more monotonously than the latter. Data were analyzed quantitatively with the concept of heat transfer within the tape and the surrounding liquid nitrogen. A heat balance equation was derived and solved, taking into consideration temperature dependence of thermal parameters of the tapes. Solutions, together with values of thermal parameters taken from the literature, explained the data well. Cooling by liquid nitrogen affected the quench development considerably at lower applied voltages. Dependence on applied voltages could be also understood quantitatively.