• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 하계학술대회 논문집 Vol.8
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• pp.238-239
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• 2007

The important merit of Bi-2212/Ag wire is to apply cable as round wire state. Bi-2212 high Tc superconducting wires were fabricated in order to apply Rutherford cable near the future. Various Ag ratio from 0.22 to 0.42 of Ag tubes for PID (powder-In-Tube) process were used to investigate the workability and to prevent breakage of filaments during drawing. KERI and Nexans Korea manufactured Rutherford cabling machine by ourselves. Rutherford cables with 20 - 30 strands could be fabricated by this machine. The shape of Rutherford cables were satisfied. The critical current of Bi2212/Ag round wire with 847 filaments showed 400 A at 4.2K and self field.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.397-397
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• 2011

In a low aspect ratio (LAR) tokamak reactor with a superconducting toroidal field (TF) coil, the radial build of TF coil and the shield play a key role in determining the size of a reactor. For self-consistent determination of the reactor components and physics parameters, a system analysis code is coupled with one-dimensional radiation transport code. Conceptual design study of a compact superconducting LAR tokamak reactor with aspect ratio less than 2.5 was conducted and the optimum radial build was identified. It is shown that the use of an improved shielding material and high temperature superconducting magnets with high critical current density opens up the possibility of a fusion power plant with compact size and small re-circulating power simultaneously at low aspect ratio, and that by using an inboard neutron reflector instead of breeding blanket, tritium self-sufficiency is possible with outboard blanket only and thus compact sized reactor is viable.

• Structural Engineering and Mechanics
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• 제71권3호
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• pp.271-282
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• 2019

The span record of cable-stayed bridges has exceeded 1,000 m, which makes research on the maximum possible span length of cable-stayed bridges an important topic in the engineering community. In this paper, span limit is discussed from two perspectives: the theoretical span limit determined by the strength-to-density ratio of the cable and girder, and the engineering span limit, which depends not only on the strength-to-density ratio of materials but also on the actual loading conditions. Closed form equations of both theoretical and engineering span limits of cable-stayed bridges determined by the cable and girder are derived and a detailed parametric analysis is conducted to assess the engineering span limit under current technical conditions. The results show that the engineering span limit of cable-stayed bridges is about 2,200 m based on materials used available today. The girder is the critical member restricting further increase in the span length; its compressive stress is the limiting factor. Approaches to increasing the engineering span limit are also presented based on the analysis results.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 춘계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.68-70
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• 2007

The operational characteristics of superconducting fault current limiter (SFCL) using magnetic coupling of coils were investigated. This SFCL consists of a high-Tc superconducting (HTSC) element and two coils with series or parallel connection on the same iron. This SFCL has the merit that the operational current of SFCL can be increased higher than the critical current of the superconducting element by adjusting the inductance ratio between two coils. To confirm its operation, the circuit for the fault simulation was constructed. From the measured voltage and current of the SFCL, it was confirmed that the resistance of HTSC element comprising this SFCL increased more than that of HTSC element's independent operation.

• Journal of Power Electronics
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• 제19권4호
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• pp.846-857
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• 2019

Voltage step-down converters are very popular in distributed power systems, voltage regular modules, electric vehicles, etc. However, a high step-down voltage ratio is required in many applications to prevent the traditional buck converter from operating at extreme duty cycles. In this paper, a series capacitor interleaved buck converter with a soft switching technique is proposed. The DC voltage ratio of the proposed converter is half that of the traditional buck converter and the voltage stress across the one main switch and the diodes is reduced. Moreover, by paralleling the series connected auxiliary switch and the auxiliary inductor with the main inductor, zero voltage transition (ZVT) of the main switches can be obtained without increasing the voltage or current stress of the main power switches. In addition, zero current turned-on and zero current switching (ZCS) of the auxiliary switches can be achieved. Furthermore, owing to the presence of the auxiliary inductor, the turned-off rate of the output diodes can be limited and the reverse-recovery switching losses of the diodes can be reduced. Thus, the efficiency of the proposed converter can be improved. The DC voltage gain ratio, soft switching conditions and a design guideline for the critical parameters are given in this paper. A loss analysis of the proposed converter is shown to demonstrate its advantages over traditional converter topologies. Finally, experimental results obtained from a 100V/10V prototype are presented to verify the analysis of the proposed converter.

• 조명전기설비학회논문지
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• 제21권10호
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• pp.46-51
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• 2007

본 논문에서는 두 코일의 직 병렬결합을 이용한 초전도 사고전류제한기의 사고전류제한 특성을 분석하였다. 구조는 병렬 또는 직렬로 연결된 두 코일과 두 코일 중 하나와 직렬 또는 병렬로 연결되는 초전도 소자로 구성된다. 동작원리는 사고전에는 초전도 소자는 초전도 상태에 있어 병렬 또는 직렬로 연결된 두 코일에 의해 발생되는 자속은 서로 상쇄되어 두 코일에 유기되는 전압이 제로를 유지하게 되지만 사고가 발생할 경우 초전도 소자의 저항이 발생되어 두 코일에서 발생되는 자속은 더 이상 상쇄되지 않게 된다. 따라서 두 코일에 전압이 유기되고 이에 따라 사고전류를 제한하게 된다. 단락실험을 통해 두 코일의 직 병렬결합에 따른 사고전류제한 특성을 분석하였으며 분석을 동해 사고전류제한기의 동작전류를 증가시킬 수 있음을 확인하였다.

• Tuberculosis and Respiratory Diseases
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• 제67권6호
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• pp.506-511
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• 2009

Background: The smoking prevalence in asthma patients are similar to those in the general population. Asthma and active cigarette smoking can interact to create more severe symptoms, an accelerated decline in lung function and impaired therapeutic responses. Accordingly, asthmatics with a history of smoking were examined to define the clinical characteristics and lung function of smoking asthmatics. Methods: The medical records of 142 asthmatics with a known smoking history were reviewed. The patients were divided into three groups according to their smoking history - current smokers, former smokers and non-smokers. The clinical characteristics, lung function, and annual declines of the forced expiratory volume in one second ($FEV_1$) were compared. Results: Fifty-three of the 142 patients (37%) were current smokers, 24 were former smokers (17%) and 65 were non-smokers (45%). The patients with a hospital admission history during the previous year included 16 current smokers (30%), 4 former smokers (17%) and 7 non-smokers (11%) (p=0.02). The mean $FEV_1$ (% predicted) was 76.8${\pm}$19.8%, 71.6${\pm}$21.1% and 87.9${\pm}$18.7% for current smokers, former smokers and non-smokers, respectively (p< 0.001). The $FEV_1$/forced vital capacity (FVC) (ratio, %) values were 63.6${\pm}$12.6%, 59.3${\pm}$14.9% and 72.1${\pm}$11.8% in current smokers, former smokers and non-smokers, respectively (p<0.001). The corresponding mean values for the individual $FEV_1$ slopes were not significant (p=0.33). Conclusion: Asthmatic smokers demonstrated higher hospital admission rates and lower lung function. These findings suggest that the smoking history is an important predictor of a poor clinical outcome in asthma patients.

• 한국초전도ㆍ저온공학회논문지
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• 제10권1호
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• pp.42-47
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• 2008

In this paper, the fault current limiting characteristics for the superconducting fault current limiter(SFCL) using magnetic coupling between two coils were investigated. The SFCL consists of a high-$T_c$ superconducting(HTSC) element and two coils. This SFCL has different characteristics that depend on the connection form, the winding direction and the inductance ratio of two coils. The impedance and the operational current of the SFCL can be adjusted higher or lower than the resistance and the critical current of HTSC element. Therefore, the SFCL can change the amplitude of the limited fault current. To confirm it, the HTSC element was modeled and the fault current limiting characteristics of the SFCL were analysed through computer simulation. It was obtained from the analysis that the connection form and the winding direction of two coils of the SFCL were the important design parameters.

• 한국초전도ㆍ저온공학회논문지
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• 제4권1호
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• pp.99-104
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• 2002

This study deals with the optimal design of a DC reactor type high-Tc superconducting fault current limiter(SFCL). The condition in which the cost function is minimized under given constraints is one of the things to be first considered in developing SFCLS. This condition is a group of the values corresponding to the variables the cost function depends on. In this paper, the length of tape was taken as a dependent variable, the inductance of DC reactor and the turns ratio of magnetic core reactors as independent variables. For the SFCL available at the level of 6.6kV-200A, we examined 4 cases; at the fault times of 80msec, 50msec, 30msec and 10msec. Since thyristors would be utilized instead of diodes, we chose the result at 10msec as the basic data. Considering safety factor 30%, our optimal design was decided to be the inductance 570mH, the critical current over 620A, the turns ratio 0.89 and the fault time within 20msec.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제51권9호
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• pp.522-529
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• 2002

In this paper, computer simulations of the physical Phenomena occurring in the arc region before and after current zero were carried out to evaluate the thermal recovery characteristics of a Laval nozzle. A commercial CFD program "PHOENICS" is used for the simulation and the user-coded subroutines to consider the arcing phenomena were added to this program by the authors. The computed results were verified by the comparison with the test results presented by the research group of GE Co.(General Electric Company). In order to investigate the state of the arc region after current zero, the simulation was carried out with three steps. They are steady state arc simulation, transient arc simulation before current zero, and transient hot-gas flow simulation after current zero. The semi-experimental arc radiation model is adapted to consider the radiation energy transport and Prandtl's mixing length model is employed as the turbulence model. The electric field and the magnetic field were calculated with the same grid structure used for the simulation of the flow field. The post-arc current was calculated to evaluate the thermal recovery characteristics after current zero. Compared with the results obtained by GE Co., it has been found that the critical RRRV(ratio of rise of recovery voltage) will be determined previously by this study.his study.