• The Transactions of the Korean Institute of Electrical Engineers B
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• v.49 no.1
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• pp.27-31
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• 2000

This paper presents the performance evaluation of an HTS transformer. Numerical calculation by finite element method was used to evaluate the performance. BSCCO-2223 HTS tapes and double pancake winding were adopted in this design. Four double pancake windings were used in total. Among them two windings were connected in series for high voltage winding and two windings are connected in parallel for low voltage winding. Propertied of various type of the winding arrangement were examined. Characteristics of the transformer during the transient which was caused by sudden short were simulated. The current limiting effect, temperature rise and resistance growth of the superconducting winding were shown.

• KIEE International Transactions on Electrophysics and Applications
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• v.11C no.3
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• pp.58-62
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• 2001

Since Metallo-Porphyrin (MP) is very interesting compound due to its unique electronic and redox properties and it is also chemically and thermally stable, MP has been studied for potential memory and switching devices. In this study, thin films of 5,10,15,20-Tetrakis-Octadecyloxymethylphenyl-Porphyrin-Zn(II) were prepared by the Langmuir-Blodgett (LB) method and characterized by using UV/vis absorption spectroscopy and cyclic voltammetry. It was found that the proper transfer surface pressure for film deposition was 25 mN/m and the limiting area per molecule was 135 ${\AA}^2$/molecule. The current-voltage (I-V) characteristics of these films were investigated. Further details on the electrical properties of Porphyrin-Zn(II) derivative films will be discussed.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.3
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• pp.544-551
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• 2011

This paper presents the circuit arrangement and effective control method of regenerative energy storage system for an electric vehicle using super-capacitors as the braking energy storage element. A bi-directional controlled current flow of the DC-DC converters with the capacitor bank is connected in parallel with battery, and is controlled so that the whole of the braking energy is effectively absorbed into the capacitors and released back to the electric motor upon acceleration. The converter needs the series-parallel switching circuit for making the best use of the series capacitors and for limiting the step-up ratio of the boost converter. The proposed methods are verified by computer simulation and experimental set-up. They are usefully applied to the electric vehicles such as green cars, electric motorcycles, bike, etc which are power- supplied by the electric batteries.

• Proceedings of the KIPE Conference
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• 2015.07a
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• pp.487-488
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• 2015

New inverter motor drive systems consume 30%~50% less energy compared to existing motor drive systems. For inverter motor drive systems, the development of a 1200V high side driver is critical. This paper presents an advanced 1200V high side driver with low power consumption and high ruggedness. This solution implements a high voltage level shifter which consumes low power by adding a clamped VGS LDMOS driver to the conventional short pulse generator. Moreover, this paper proposes a highly rugged 1200V LDMOS which improves SOA by limiting the hole current. This paper could be applied to smart power modules used for HVAC (heating, ventilation, and airconditioning) and industrial inverters. Consequently, this paper will provide design engineers with an understanding of how they can make a significant contribution to worldwide energy savings.

• Proceedings of the KIEE Conference
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• 2005.10c
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• pp.244-249
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• 2005

본 논문에서는 전원 불평형시 일반적인 계통연계형 인버터의 유효전력의 리플을 효과적으로 제거하는 동시에 인버터의 운전가능 영역을 제한해 반도체 스위치 소자를 보호하면서 운전하는 방법을 제안한다. 헌재 불평형된 전압의 정보로부터 계통연계 인버터가 반도체 스위치 소자의 전류 정격을 넘지 않고 처대로 출력할 수 있는 유효전력량을 실시간으로 계산하고 계통으로 출력되는 전력이 이 값을 넘지 않도록 제어한다. 시뮬레이션과 실험을 통해 제안된 전력제한 알고리즘의 동작특성을 검증하였다.

• Bulletin of the Korean Chemical Society
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• v.20 no.11
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• pp.1303-1308
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• 1999

Conducting poly(3,4-ethylenedioxythiophene) (PEDT) films with metalloporphyrins incorporated as the counter ions were prepared by electropolymerization of the monomer in the presence of metal-tetra(sulfonatophenyl) porphyrin anions. Cathodic reduction of oxygen on the resulting conducting polymer films was studied. The overpotential for O2 reduction on electrodes with cobalt-porphyrin complex was significantly smaller in acidic solutions than on gold. In basic solutions, the overpotential at low current densities was close to those on platinum and gold. Polymer electrode with Co-complex yielded higher limiting currents than with Fe-complex, although the Co-complex polymer electrode was a poorer electrocatalyst for O2 reduction in the activation range of potential than the Fe counterpart. From the rotating ring-disk electrode experiments, oxygen reduction was shown to proceed through either a 4-electron pathway or a 2-electron pathway. In contrast to the polypyr-role-based electrodes, the PEDT-based metalloporphyrin electrodes were stable with wider potential windows, including the oxygen reduction potential. Their electrocatalytic properties were maintained at temperatures up to 80℃ in KOH solutions.

• Structural Engineering and Mechanics
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• v.71 no.3
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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.

• Bulletin of the Korean Chemical Society
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• v.19 no.2
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• pp.183-188
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• 1998

Incorporation of metalloporphyrins into polypyrrole (PPy) film was achieved either by electropolymerization of pyrrole in the presence of metal-tetra(sulfonatophenyl)porphyrin anion (MTSPP, M=Co, Fe) or by metalizing hydrogenated tetra(4-sulfonatophenyl)porphyrin anion (H2TSPP) doped into PPy through ion-exchange. Electrochemical reduction of oxygen on the PPy doped with metallo porphyrin (PPy-MTSPP) was studied in acidic and basic solutions. Oxygen reduction on PPy-MTSPP electrodes appeared to proceed through a 4-electron pathway as well as a 2-electron path. In acidic solutions, the overpotential for O2 reduction on PPy-CoTSPP electrode was smaller than that on gold by about 0.2 V. In basic solutions the overpotential of the PPy-CoTSPP electrode in the activation range was close to those of Au and Pt. The limiting current was close to that of Au. However, polypyrrole doped with cobalt-tetra(sulfonatophenyl)porphyrin anion (PPy-CoTSPP) or with iron-tetra(sulfonatophenyl)porphyrin anion (PPy-FeTSPP) was found to have limited potential windows at high temperatures (above 50 ℃), and hence the electrode could not be held at the oxygen reduction potentials in basic solutions (pH 13) without degradation of the polymer.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05b
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• pp.166-172
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• 1996

The thermal-hydraulic effects of removing the RCC guide thimble plugs are evaluated for Westinghouse type PWR plants as a part of feasibility study: core outlet loss coefficient, thimble bypass flow, and best estimate flow. It is resulted that the best estimate thimble bypass flow increases about by 2% and the best estimate flow increase approximately by 1.2%. The resulting DNBR penalties can be covered within the current DNBR margin. Accident analyses are also investigated and the dropped rod transient is shown to be limiting and relatively sensitive to bypass flow variation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.1
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• pp.1-8
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• 2010

Natural convection heat transfer rates in a vertical pipe were measured for $Gr_H$ number from 2.1x$10^6$ to 1.2x$10^9$. Using the analogy concept, heat transfer experiments were replaced by mass transfer experiments. A cupric acid - copper sulfate ($H_2SO_4-CuSO_4$) electroplating system was adopted as the mass transfer system and the mass transfer rates were measured. Comparison of the results with the existing laminar and turbulent natural convection heat transfer correlations on a vertical plate showed very good agreements except for the high $Gr_H$ case, where the boundary layer inside the vertical pipe interferes. The agreements showed the usefulness of the analogy experiment method. Using 3 different anode size and 6 different geometrical configurations, the effects of the anode size and position were explored. As expected, the anode size and position do not affect the limiting currents for most cases. These results will be used as the experimental background for the positioning and sizing of the anodes for a more complex experiment.