• Journal of Welding and Joining
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• 제10권4호
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• pp.250-258
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• 1992

In order to clarify the mechanical behavior of welding crack and to evaluate the mechanical characteristics of welded parts in thick plate, it is very important to accurately predict the welding deformation and residual stress including transient state before welding. In this paper, the theory of a three-dimensional elasto-plastic problem for the analysis of mechanical phenomenon of welding joint on the plate is developed into an efficient and accurate method based on the finite element method, and then several examples are considered by using the proposed model. The results of numerical analyses are discussed in the viewpoint of the mechanical characteristics of the distribution of three-dimensional welding residual stresses, plastic strains and their production mechanism on the thick plate.

• 산업기술연구
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• 제24권A호
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• pp.75-81
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• 2004

The metal halide lamps are now widely used in the application and commercial lighting due to their attracting properties such as good color rendering and high efficiency. But, they have the serious problem of acoustic resonance for high frequency operation and they need the high voltage to ignite. So, they have not been applied to indoors. Over the past few years, a considerable number of studies have been conducted on the electronic ballast together with hot restarting and resonance phenomenon. But, very few attempts have been made with the adaptive ignition method according to the lamp state. In this paper, electronic ballast is proposed for metal halide lamps with an igniter for adaptive ignition. The proposed electronic ballast can generate different ignition voltages according to the arc tube state.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• 제4B권1호
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• pp.24-28
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• 2004

Metal halide lamps have been made suitable for use in outdoor illumination systems over many years. They are also widely used in application and commercial lighting due to their attracting properties such as good quality color, rendering and high efficiency. Over the past few years, a considerable number of studies have been conducted on the electronic ballast with hot restarting and resonance phenomenon. However, very few attempts have been made at the adaptive ignition method according to lamp state. This paper proposes an electronic ballast for metal halide lamps with an igniter for adaptive ignition. The proposed electronic ballast can generate different ignition voltages according to the arc tube state. The experimental results showed that the proposed ballast circuit using adaptive igniter is suitable for 70W HQI lamps.

• 천문학회지
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• 제13권1호
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• pp.1-8
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• 1980

Simultaneous observations of high resolution spectra of CaII H, K, ${\lambda}8542\;and\;{\lambda}8498$ have been made over a sunspot umbra (SPO 5007) by means of Sacramento Peak Observatory's HIRKHAD program with the Echelle spectrograph at the Vacuum Tower Telescope. The observed spectra scanned by SPO's fast microphotometer have been reduced for later theoretical interpretations. The reduced profiles, sampled over a region which is thought to be coolest over the spot, are presented in units of absolute intensity. The core intensity ratios of $I(K_3)/I(H_3);and\;I({\lambda}8498)/I({\lambda}8542)$ arc found to be 1.3 and 1.14, respectively.

• 대한전기학회논문지:전력기술부문A
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• 제55권11호
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• pp.468-475
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• 2006

This paper reviews the energy characteristics of oil filled cables in transient state such as grounding fault and lightning surge. Artificial grounding fault test was firstly performed in 2003 for the analysis of arc voltage and breakdown energy according to the fault current. In this paper, energy of OF cable is variously analysed at joint box based on the actual test. Then more various conditions such as installation types, section lengths and CCPU(Cable Covering Protection Unit) connection types are applied for the simulation using EMTP when the single line to ground fault and direct lightning stroke are occurred on actual underground power cable systems and combined power cable systems, respectively. Finally, the energy by the length of crossbonded lead and grounding lead as well as fault lasting time is also calculated using EMTP simulation.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2012년도 전력전자학술대회 논문집
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• pp.230-231
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• 2012

This paper describes a gate driver that operates numerous semiconductor switch in the solide-state pulsed power modulator. the proposed gate driver is designed to receive both the isolated drive-power and the on/off pulse signals through the transformer. Moreover, the IGBT-switch can be quickly turned off by adding protection circuit. Therefore it protects the IGBT-switch from the arc condition that frequently occurs in high-voltage pulse application. To comprehend operating characteristic of each IGBT-switch in pulse output condition, the device consisting of a high efficiency soft-switching capacitor charger and two series stacking IGBT-switch is developed. Finally, the relability of the proposed gate driver and the device for its test are proved through PSpice simulation and experiments.

• 한국항공우주학회지
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• 제47권2호
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• pp.90-97
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• 2019

스파크제트 액츄에이터는 플라즈마 합성 제트 액츄에이터(plasma synthetic jet actuator, PSJA)라고도 불리는 능동 유동 제어 장치로, 초음속 유동의 제어 가능성이 있어 많은 연구가 진행 중이다. 이 액츄에이터는 아크 플라즈마를 이용해 캐비티(cavity) 내부에 에너지를 주입하여 온도와 압력을 상승시킨다. 온도와 압력이 상승한 캐비티에서 오리피스(orifice)를 통해 압력파와 제트가 분출되어 외부 유동에 교란을 준다. 플라즈마의 영향으로 캐비티 유동은 고온, 고압의 평형 유동이 되기 때문에 스파크제트 액츄에이터의 유동 해석을 위해선 공기의 평형 상태를 고려해야 한다. 본 연구에서는 평형 유동의 특성을 고려하여 스파크제트 액츄에이터 유동 해석을 위한 수치해석 프로그램을 개발했다. 개발된 프로그램의 검증으로 문헌에서 얻을 수 있는 실험 결과와 시간에 따른 제트의 위치를 비교했다. 또한 상온, 상압의 무풍에서 액츄에이터의 추력 특성을 분석했다.

• 한국분말재료학회지
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• 제15권5호
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• pp.352-358
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• 2008

The present study focused on the synthesis of a bismuth-antimony-tellurium-based thermoelectric nanopowders using plasma arc discharge process. The chemical composition, phase structure, particle size of the synthesized powders under various synthesis conditions were analyzed using XRF, XRD and SEM. The powders as synthesized were sintered by the plasma activated sintering. The thermoelectric properties of sintered body were analyzed by measuring Seebeck coefficient, specific electric resistivity and thermal conductivity. The chemical composition of the synthesized Bi-Sb-Te-based powders approached that of the raw material with an increasing DC current of the are plasma. The synthesized Bi-Sb-Te-based powder consist of a mixed phase structure of the $Bi_{0.5}Sb_{1.5}Te_{3}$, $Bi_{2}Te_{3}$ and $Sb_{2}Te_{3}$ phases. This powder has homogeneous mixing state of two different particles in an average particle size; about 100nm and about 500nm. The figure of merit of the sintered body of the synthesized 18.75 wt.%Bi-24.68 wt.%Sb-56.57 wt.%Te nanopowder showed higher value than one of the sintered body of the mechanically milled 12.64 wt.%Bi-29.47 wt.%Sb-57.89 wt.%Te powder.

• 한국분말재료학회지
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• 제22권3호
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• pp.181-186
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• 2015

In this study, the effect of the friction stir welding (FSW) was compared with that of the gas tungsten arc welding (GTAW) on the microstructure and microhardness of Cu-Ni alloy weldment. The weldment of 10 mm thickness was fabricated by FSW and GTAW, respectively. Both weldments were compared with each other by optical microstructure, microhardness test and grain size measurement. Results of this study suggest that the microhardness decreased from the base metal (BM) to the heat affected zone (HAZ) and increased at fusion zone (FZ) of GTAW and stir zone (SZ) of FSW. the minimum Hv value of both weldment was obtained at HAZ, respectively, which represents the softening zone, whereas Hv value of FSW weldment was little higher than that of GTAW weldment. These phenomena can be explained by the grain size difference between HAZs of each weldment. Grain size was increased at the HAZ during FSW and GTAW. Because FSW is a solid-state joining process obtaining the lower heat-input generated by rotating shoulder than heat generated in the arc of GTAW.

• 전력전자학회논문지
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• 제8권1호
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• pp.24-29
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• 2003

현재 120kV/70A 고압 스위치가 KSTAR의 NBI 시스템에 사용되기 위하여 대전의 원자력 연구소에 설치되어 있다. NBI 시스템은 아크 발생시 이온 소스를 보호하기 위하여 전압의 빠른 차단 및 빔 전류의 유시를 위하여 전압의 빠른 턴온이 요구된다. 따라서 고압 스위치와 아크 검출회로는 NBI 시스템에서 중요한 부분을 차지하고 있다. 고압의 반도체 스위치는 NBI 시스템 뿐만 아니라 산업전반에서 요구되고 있다. NBI 시스템에 적용된 120kV/70A 고압 스위치는 100개의 MOSFET 소자를 직렬연결하였으며 본 논문에서 제안한 바이어스 전원이 없는 간단한 구동회고를 사용하였다. 실험식에서의 시험 및 현장에서 100kW의 모의 저항부하와 NBI 이온 소스에 적용한 실험결과를 제시하였다. 본 논문은 120kV/70A 고압 MOSFET 스위치와 간단한 게이트 구동회로의 설계를 제시하였으며, 제작 및 시험기간 동안의 문제점 및 해결방안에 대해서도 제시하였다.