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AlGaN-based deep ultraviolet light-emitting diodes on nanopatterned AlN/sapphire substrates
Donghyun LEE,Jong Won LEE,Jeonghwan JANG,In-Su SHIN,Lu JIN,Jungsub KIM,Jinsub LEE,Hye-Seok NOH,Yong-Il KIM,Youngsoo PARK,Gun-Do LEE,Yongjo PARK,Jong Kyu KIM,Euijoon YOON 한국진공학회 2016 한국진공학회 학술발표회초록집 Vol.2016 No.8
Lee, Woo Seung,Nam, Seokho,Kim, Jinsub,Lee, Jeyull,Ko, Tae Kuk IEEE 2015 IEEE transactions on applied superconductivity Vol.25 No.3
<P>Most superconducting devices are designed for a fixed operating temperature range, however, temperature varia- tions are inevitable in some situations. For example, the temperature of a resistive-type superconducting fault current limiter becomes higher during fault cycle operation. Therefore, knowledge of the temperature dependence of the current-to-voltage characteristic is necessary for accurate simulation or design processes. This paper explores the temperature dependence of the n-index, which describes sharpness of superconductivity to normal transition, using a second-generation high-temperature superconducting tape sample under a liquid nitrogen surrounded environment. The voltage across the sample according to given current and temperature is measured by establishing a measurement system with a protection system. The average of the data from multiple measurements is calculated and compared with three different n-index models. Constant, inversely proportional, and modified inversely proportional models are analyzed. The modified inversely proportional model showed the least error when compared to the measurement data.</P>
Effects of AC Disturbance on Cowinding HTS Coils According to the Inserted Materials
Jinsub Kim,Young Jin Hwang,Woo Seung Lee,Tae Sung Lee,Jeyull Lee,Tae Kuk Ko Institute of Electrical and Electronics Engineers 2015 IEEE transactions on applied superconductivity Vol.25 No.3
<P>Alternating field causes energy loss due to induced back electromotive force (EMF) to high-temperature superconducting (HTS) coils in the superconducting electric machines. Therefore, a method of reducing the effects of the alternating fields on the HTS coils in superconducting machines according to the winding insulation conditions has been investigated. In addition, the HTS coils cowound with turn-to-turn inserted materials to control the time constant has been proposed. The charge-discharge delay can be determined with the time constant, also the time constant is related to the radial directional resistance of the no-insulation coil. The variation of the radial resistance would affect the reduction effect of ac disturbance on the no-insulation coil. Therefore, trade-off between the reduction effect of the alternating disturbance and charge-discharge delay could be considered. In this paper, we evaluated the effects of alternating magnetic fields on the HTS coils according to the varying radial resistance caused by cowinding method with metal tapes in liquid nitrogen. Four types of the HTS coils are: 1) no-insulation coil, 2) cowound coil with copper tape, 3) cowound coil with stainless steel tape and 4) insulation coil which have different radial resistance respectively. The experimental result shows that the co-winding method can be applicable in the superconducting electric machines.</P>
Jeyull Lee,Junseong Kim,Jinsub Kim,Young Gun Park,Woo Seung Lee,Jiho Lee,Yoon Do Chung,Kyung-yong Yoon,Ho Min Kim,Yong Soo Yoon,Tae Kuk Ko Institute of Electrical and Electronics Engineers 2016 IEEE transactions on applied superconductivity Vol.26 No.4
<P>In this paper, characteristics of a thermally and magnetically triggered switch for a high-Tc superconducting (HTS) power converting system are experimentally analyzed. For verifying the efficiency of the suggested switch, current charging and discharging tests using heater-triggered switch with or without an external magnetic field are performed. Charging tests are performed with two charging sequences, i.e., CS1 and CS2. Each sequence is experimented with two kinds of heater currents to maintain different temperatures. Saturation current and saturation time are detected to calculate the pumping rate. Two discharging sequences, i.e., DS1 and DS2, are used for discharging tests with heater current to maintain 120 K. From the results, normalized load energies are calculated and compared.</P>