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Study on Reliability Improvement of Voltage Transformers by Increasing Voltage Factor
Tae‑Sik Kong,Hee‑Dong Kim,Hung‑Sok Park,Soo‑Hoh Lee,Soon‑Yong Kim,Pil‑Bum Joung,Jin‑Yeub Park 대한전기학회 2020 Journal of Electrical Engineering & Technology Vol.15 No.3
Voltage transformers (VTs) must be highly reliable as they are essential components of the electric power industry. VT failures can cause a signifcant impact for important facilities such as nuclear power plants. In fact, VTs which passed the international standard, were damaged and sometimes resulted in the shutdown of the nuclear power plants. In order to improve the reliability, VTs with various iron core was studied. The electromagnetic feld simulation, a saturation characteristics test, and an overvoltage breakdown test were conducted. The result shows that the magnetic fux density signifcantly afects the reliability of VTs. To increase the reliability of VTs, it is required to reduce the magnetic fux density by increasing the knee-point and voltage factor. Owing to limited installation space, increasing the size of the iron core is difcult. Instead, VT by decreasing the thickness of the conductor and increasing the number of turns, it was possible to reduce the magnetic fux density without the size change. Therefore, improved VTs were obtained by decreasing the thickness of the conductor and increasing the number of turns, and the improved reliability was verifed through a comparison test with existing VTs. The fabricated VTs shows a signifcantly higher saturation voltage and breakdown time than existing VTs. Thus, by proposed VTs can contribute the stable operation of the nuclear power plant and improve the manufacturer’s quality.
국내 아스팔트 포장의 소성변형으로 인한 유지보수 비용 및 방지대책에 관한 연구
고석범,김수삼,박태순 중앙대학교 생산공학연구소 1999 생산공학연구소 논문집 Vol.8 No.2
본 연구는 아스팔트 포장의 현장조사 자료를 근거로 기존 포장을 유지보수하기 위하여 사용한 과거 10년간의 예산사용액을 타토목구조물과 비교 검토하였으며, 소성 변형으로 인한 문제점, 소성변형에 영향을 미치는 인자를 분석하였다. 특히, 우리나라 소성변형 발생원인 및 특성, 소성변형 발생 장소 및 유형을 조사 분석하여 소성변형 방지방안에 대해 검토하였다. 본 연구는 아스팔트 포장의 소성변형으로 인하여 매년 증가하고 있는 유지보수 비용을 절감하는데 연구의 목적이 있다. The study was compare and review the budget of other civil structure with that which has been used to maintain and repair the old pavement for ten years on the field investigation data of asphalt pavement as well as to analyze the problems occurred by the plastic deformation and the factors affecting plastic deformation. In especial, the method to prevent plastic deformation was reviewed by analyzing the causes and characteristics, place, type which plastic deformation has occurred in Korea. The purpose of this study is to decrease the cost of maintenance thtat had been increased due to the plastic deformation of asphalt pavement.
隔板을 가진 水平環狀空間에서 自然對流에 관한 實驗的 硏究
鄭泰鉉,金善政,李範澈,權純錫 동아대학교 공과대학 부설 한국자원개발연구소 1988 硏究報告 Vol.12 No.2
Natural convection from a horizontal annulus with spacers has been studied on the effects of Rayleigh numbers and position of spacers by experimental method. In case of vertical spacers, the maximum local Nusselt number appears at θ=150° in a conducting tube and θ=30° in a cylinder. The local spacer Nusselt numbers show positive values on the lower spacer, but negative values on the upper spacer. In case of horizontal spacers, the flow over the spacer is more active than that of under the spacer as the Rayleigh number increase. The maximum local Nusselt number appears at θ=180° In a tube and at θ=0° in a cylinder. The local spacer Nusselt number show positive values on the upward surface of spacer, but negative values on the downward surface of spacer. The mean tube Nusselt numbers and mean cylinder Nusselt numbers with vertical spacer are increased 11% And 2.7%, respectively by those of horizontal spacer.
대전·충남지역 고등학교 1학년생의 풍진 항체보유율과 백신접종 후의 항체형성률
오성균,김수영,여경오,김윤태,최명한,이석구,조영채,이동배,이태용 충남대학교 의과대학 지역사회의학연구소 1998 충남의대잡지 Vol.25 No.2
For the purpose of investigating the positive rate of rubella antibody and sero-conversion rate after rubella vaccination, 863 high school students of the two regions were studied from April 21st, 1996 to September 20th, 1996. The main results were as follows; 1. Positive rate of IgG in male was higher than in female, and the rate of IgM was also higher in male than in female. 2. Positive rate of IgG by blood type was similar, but positive rate of IgM was higher in AB type than the others. 3. Positive rate of IgG by vaccination was similar to all groups, but positive rate of IgM was higher in which was not vaccinated group. 4. Positive rate of IgG and IgM, having vaccination card, was less than which was not having vaccination card. 5. Those who were vaccinated acquired IgG(+) regardless of an existence of IgG antibody, and 28.3% of IgG(-), IgM(+) male who was not vaccinated became IgM(+), IgG(+) after 3months later. As a result positive rate of male was higher than female. The author conclude that vaccination is necessary to prevent from rubella for them.
A Study on the Hedging Effectiveness of Exotic Currency Options : KIKO, Pivot, and Snowball
Sok Tae Kim 한국무역연구원 2010 The International Academy of Global Business and T Vol.6 No.2
The objective of this study is to examine the hedging effectiveness of the exotic currency options, especially circulated as in Korea prior to and during the global financial crisis of 2006~2008. In the view that the primary goal of hedging is to reduce the volatility of the portfolio with hedging instruments and hedged instruments combined, hedging effectiveness should be screened on three matching principles: first, there should be a match of duration between the hedging and hedged. Second, there should be a match between the money amount of the hedged instrument and the hedging instrument. Third, the material characters of the hedging and hedged should be matched throughout the hedging period. The three exotic currency options, which were introduced and damaged significantly many small and medium sized Korean firms, a lack of the three hedging principles in the three matching principles is noted. Thus, it can be concluded that those exotic currency options should not have been used as hedging instruments for non-financial exporting firms at all.
Greater Integration of Global Financial Markets and Rising Risks
Sok-Tae Kim 한국무역연구원 2011 貿易 硏究 Vol.7 No.2
The objective of this study is to examine the characteristics of risks with integration of global markets more intensified and to offer measures to mitigate those risks in a more effective way. In effect, global financial markets have been tied-up so closely that financial crisis in one region can be spilled over to other regions in quite a diverse and prompt manner, making it more difficult to prevent a regional shock from becoming a devastating global crisis. Those risks frequently change their forms, easily crossing borders affecting other seemingly unrelated regions. Thus, to prevent or to mitigate those risks in a proactive way, instead of conventional measures which are independently and segmentally operated, more systematic multi-layer measures should be adopted from the global level, regional and local level perspective, including IMF reform, global based regulations on hot money flows and OTC derivatives.