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Characteristics of joint resistance with different kinds of HTS tapes for heater trigger switch
Jeyull Lee,Young Gun Park,Woo Seung Lee,Hyun Chul Jo,Yong Soo Yoon,Tae Kuk Ko 한국초전도저온공학회 2014 초전도와 저온공학 Vol.16 No.1
Recently, many researches on the system of superconducting power supply and superconducting magnetic energy storage (SMES) using high temperature superconducting (HTS) tapes has been progressed. Those kinds of superconducting devices use the heater trigger switches that have a control delay problem at moments of heating up and cooling down. One way to reduce the time delay is using a different HTS tape at trigger part. For example, HTS tape having lower critical temperature can reduce time delay of heating up and heating down stage for heater trigger operation. This paper deals with resistances joint with different kinds of HTS tapes which have different properties to verify usefulness of the suggested method. Three kinds of commercial HTS tapes with different specifications are selected as samples and two kinds of solders are used for comparison. Joint is performed with temperature and pressure controllable joint machine and the joint characteristics are analyzed under the repeatable conditions.
Lee, Jeyull,Kim, Junseong,Baek, Geonwoo,Choi, Yojong,Choi, Yoon Hyuck,Zhang, Zhan,Chung, Yoon Do,Kang, Hyoungku,Lee, Haigun,Lee, Sangjin,Ko, Tae Kuk IEEE 2018 IEEE transactions on applied superconductivity Vol.28 No.3
<P>High-temperature superconductors (HTSs) have a much larger thermal margin than low-temperature superconductors, owing to their high critical temperatures. This characteristic allows HTS magnets to tolerate extremely high heat loads that may arise from radiation. Therefore, research on the development of HTS quadrupole magnets is progressing widely. Quadrupole magnets are commonly used for focusing the transported beams of particles in accelerators. In order to focus the beam, the quadrupole magnet uses an iron yoke with a hyperbolic contour. However, the iron yoke induces nonlinear magnetic characteristics because of saturation. Therefore, an air-core HTS quadrupole magnet is proposed to improve the magnetic characteristics. In this paper, we design air-core and iron-core HTS quadrupole magnet models using a harmonic matching method. The field gradient and effective length of both magnets are 12.1 T/m and 550 mm, respectively. In order to verify the performances of the proposed air-core quadrupole magnet, the magnetic field gradient, field uniformity, and effective length are analyzed for operating currents ranging from 50 to 400 A.</P>
Characteristics of joint resistance with different kinds of HTS tapes for heater trigger switch
Lee, Jeyull,Park, Young Gun,Lee, Woo Seung,Jo, Hyun Chul,Yoon, Yong Soo,Ko, Tae Kuk 한국초전도저온공학회 2014 한국초전도저온공학회논문지 Vol.16 No.1
Recently, many researches on the system of superconducting power supply and superconducting magnetic energy storage (SMES) using high temperature superconducting (HTS) tapes has been progressed. Those kinds of superconducting devices use the heater trigger switches that have a control delay problem at moments of heating up and cooling down. One way to reduce the time delay is using a different HTS tape at trigger part. For example, HTS tape having lower critical temperature can reduce time delay of heating up and heating down stage for heater trigger operation. This paper deals with resistances joint with different kinds of HTS tapes which have different properties to verify usefulness of the suggested method. Three kinds of commercial HTS tapes with different specifications are selected as samples and two kinds of solders are used for comparison. Joint is performed with temperature and pressure controllable joint machine and the joint characteristics are analyzed under the repeatable conditions.
Jeyull Lee,Young Gun Park,Hyun Chul Jo,Ho Min Kim,Yoon Do Chung,Yong Chu,Tae Kuk Ko,Yong Soo Yoon IEEE 2016 IEEE transactions on applied superconductivity Vol.26 No.3
<P>This paper presents experimental results of the designed high-Tc superconducting (HTS) power converting system with multiple GdBCO magnets. The system is tested by various sequential controls of four heater-triggered switches and an electromagnet, which consists of two energy storage magnets (ESMs). The experiments are mainly composed of two modes. The first one is a simultaneously operating mode (Mode1), and another is an alternative operating mode (Mode2). Each two sequences are performed at Mode1 (CS1 and CS2) and Mode2 (CS3 and CS4) for charging the ESMs, respectively. In those experiments, the average pumping rate of each sequence is calculated at about 17.55, 41.26, 10.25, and 25.83 mA/s, respectively. In the discharging test, two sequences are tested. Load energy is calculated from load voltage and current due to the difference between precharged energy to verify which operating mode is more effective. Load energy of each sequence reached about 47.97 and 38.83 J after 2000 s, respectively.</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>
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>
Lee, Jeyull,Jeon, Haeryong,Han, Seunghak,Kim, Ji Hyung,Hyeon, Chang Ju,Kim, Ho Min,Ko, Tae Kuk,Park, Dong Keun,Yoon, Yong Soo Institute of Electrical and Electronics Engineers 2018 IEEE transactions on applied superconductivity Vol.28 No.3
<P>In this paper, the charging characteristics of high-Tc superconducting (HTS) field coils are analyzed experimentally to verify the efficiency of using HTS contactless rotary excitation devices (CREDs). The HTS CRED is composed of eight HTS rotor strands, which are connected in series with HTS load coils, and eight neodymium permanent magnets (N50). The magnetic field of N50 is approximately 0.14 T when the air gap between the HTS rotor strand and N50 is 8 mm. In order to verify the proper charging method, two types of experiments are performed. In the first experiment, the HTS loads are connected in series and are charged by eight HTS rotor strands of the HTS CRED. In the second, the HTS loads are located along the same axis, and each coil is charged by four HTS rotor strands of the HTS CRED. In these experiments, the currents flowing through the HTS loads are measured for rotor speeds ranging from 50 to 300 r/min.</P>
안드로이드 플랫폼 기반 명함 인식 어플리케이션을 위한 명함 영역 검출 기법
이제율 ( Jeyul Lee ),이규원 ( Kyuwon Lee ) 한국정보처리학회 2014 한국정보처리학회 학술대회논문집 Vol.21 No.1
본 논문에서는 다양한 형태의 어플리케이션 중 스마트폰에 탑재된 카메라를 이용하여 명함을 인식할 때 발생하는 문제점을 해결하기 위한 기법을 제시하고자 한다. 스마트폰의 카메라를 이용하여 이미지를 얻을 경우 카메라의 각도에 따라 객체의 모양이 변형된다. 명함인식에서 이러한 이미지 왜곡문제는 인식률에 많은 영향을 미친다. 본 논문에서는 카메라의 각도에 따른 이미지의 왜곡 문제를 해결하기 위해 캐니 에지를 이용하여 객체를 검출하고, 검출된 객체의 간단한 정보를 이용하여 명함 영역을 검출하고, 영역 내에 명함을 검출하는 기법을 제안한다.
Seokho Nam,Woo Seung Lee,Jeyull Lee,Haeryoung Jeon,Seunghak Han,Yojong Choi,Jiho Lee,Tae Kuk Ko Institute of Electrical and Electronics Engineers 2017 IEEE transactions on applied superconductivity Vol.27 No.4
<P>A current lead is a connecting device between the superconducting magnet and the power supply. A large amount of heat transfer ocurrs through the current lead because the cold-end in a superconducting system is thermally linked with the warm-end part. Therefore, high-Tc superconductor (HTS) is used in the current lead for a tokamak system. However, it is hard to consider the dependance of HTS's critical current with respect to temperature because the conventional HTS current leads consist of the HTS tapes with the same width and thickness, and their critical currents can differ from their temperature. For this reason, cold-end of the HTS section in current lead is designed excessively than necessary specifications. This generates the additional heat transfer between cold-end and warm-end within the HTS current lead. In this paper, a study on the HTS current leads with asymmetric structure is conducted to reduce the heat transfer by reducing the cross-sectional area of the HTS current lead. Asymmetric current leads are fabricated considering the design parameters about heat transfer within the HTS current lead. Current transporting tests on the conventional, symmetrical, and asymmetrical HTS current leads are performed to confirm the feasibility of the suggested design. And then, heat load of the asymmetric current lead is compared with the symmetric current lead. From this study, it is found that heat load of the current lead is reduced by using the asymmetric HTS current lead.</P>