• 한국유체기계학회 논문집
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• 제6권3호
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• pp.58-63
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• 2003

The performance of turbo pump drops rapidly and it gets into break-down when the void fraction reaches above the threshold value because the impeller flow passage is choked up with air bubbles. Phenomenological understanding of break-down and pumping recovery mechanisms under air-water two-phase flow conditions are therefore important for pump designers and essential assignment for researchers. In this paper, we investigated the characteristics of break-down and pumping recovery due to entrained air occurring inside a screw-type centrifugal pump which has a wide flow passage mainly through the findings of suction and discharge pressures, rotational speed, flow rate measurements and visualization.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.770-773
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• 2003

To measure discharge breakdown acoustic signal, Fabry-Perot interferometer fiber optic sensor is used. Fiber optic sensor array can measure the partial discharge acoustic signal caused by defect of power facilities such as power cables, transformers and gas insulation. Fabry-Perot interferometer is selected as an fiber optic sensor array. It is shown that Fabry-Perot fiber optic sensor array detected discharge breakdown acoustic signal, effectively.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2011년도 제42회 하계학술대회
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• pp.21-22
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• 2011

In this paper, considerations on correlation between partial discharge and breakdown using void-simulated defect, investigating the characteristics of void discharges. For the purpose, the relationship between PDIV(Partial Discharge Inception Voltage) and BDV(BreakDown Voltage) was analyzed. As a result, it is noticed that the higher PDIV, the higer BDV.

• 한국세라믹학회지
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• 제24권4호
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• pp.392-396
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• 1987

Pure barium titanate was sintered at $1340^{\circ}C$ for 2, 4, 8, 16 hr to control their grain size. The measurements of breakdown strength and partial discharge characteristics were performed under rising AC voltage(60Hz). With increase of sintering time, the average grain size was increased and breakdown strength was slightly decreased. Partial discharge in pores was observed under high voltage, and a model of dielectric break down in barium titanate ceramics is proposed.

• 전기의세계
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• 제19권6호
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• pp.18-25
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• 1970

The object of this project is to manifest the mechanism of deterioration phenomena for dielectrics causing corona discharge and applies it for determine the standard corona detection technique. As the results, we observed that corona discharges may occur more strongly around cylindrical shape electrode in air than hemisphere shape electrode in vacuum, so that it depends on effects such as shape of the electrode, moisture, surface coditions, etc. According to observed the deterioration of dielectrics takes place in following stages. At first the attacked surface by an electron avalanche is uniformly eroded; then pits are formed; after that sharp channels are formed which lead to break-down as a treeing. The test are accelerated with higher frequencies by the cylindrical bar shape electrode in the pulse stright detection method more sensitive than Lissajous patterns. Lissajous patterns detection method is simple but usually insensitive and has disadvantage that the magnitude of the individual discharge is not measured.

• Nuclear Engineering and Technology
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• 제54권1호
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• pp.152-161
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• 2022

We analyzed mitigation strategies for steam generator tube rupture (SGTR) accidents using MARS code under both full-power and low-power and shutdown (LPSD) conditions. In general, there are two approaches to mitigating SGTR accidents: supplementing the reactor coolant inventory using safety injection systems and depressurizing the reactor coolant system (RCS) by cooling it down using the intact steam generator. These mitigation strategies were compared from the viewpoint of break flow from the ruptured steam generator tube, the core integrity, and the possibility of the main steam safety valves opening, which is associated with the potential release of radiation. The "cooldown strategy" is recommended for break flow control, whereas the "RCS make-up strategy" is better for RCS inventory control. Under full power, neither mitigation strategy made a significant difference except for on the break flow while, in LPSD modes, the RCS cooldown strategy resulted in lower break and discharge flows, and thus less radiation release. As a result, using the cooldown strategy for an SGTR under LPSD conditions is recommended. These results can be used as a fundamental guide for mitigation strategies for SGTR accidents according to the operational mode.

• 한국수자원학회논문집
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• 제49권2호
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• pp.121-132
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• 2016

본 연구에서는 DAMBRK 모형을 2002년 태풍 루사로 인해 붕괴된 남대천 유역의 장현저수지와 동막저수지에 적용하여 붕괴상황을 재현하였다. 두 저수지는 병렬로 위치하고 있으며, 이 두 저수지의 붕괴 모의를 위해 Relaxation 기법을 DAMBRK 모형에 추가하였다. 그리고 ASDSO (2005)에서 제안한 흙댐 붕괴지속시간과 첨두붕괴유량 산정을 위한 Froehlich 등의 경험공식을 활용한 저수지의 붕괴지속시간 추정 방법을 제안하였다. 제안 방법으로 선정된 붕괴지속시간으로 장현저수지 단일붕괴와 장현 및 동막저수지 연속붕괴에 대해 적용하여 붕괴유출 수문곡선을 계산하였다. 계산된 붕괴유량이 하류로 전파하면서 예상되는 홍수량 및 홍수위를 주요 하도지점에서 계산하고, 유량이 감쇠되는 특성을 해석하였다. 그리고 계산 홍수위와 현장 조사된 홍수위와의 비교를 통해 적용 모형의 매개변수 및 정확성을 검증하였다.

• 전기의세계
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• 제14권2호
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• pp.8-13
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• 1965

It is expected that the impurities contained in a solid state insulation material will affect a considerable influence on its break-down voltage, dielectric loss, and insulation resistance. In this thesis, as a preliminary experimental research for the investigation described above, the effect of metalic barrier between the electrodes on the creepin flash over discharge voltage along the surface of a solid insulation material has been investigated, and got some interesting results. It was found that generaly the flash over voltage rises when a metalic barrier is located between the electrodes. The results of this investigation will be taken into account as an important components on the insulation design to prevent the creeping flash over discharge in insulators, bushings, and so on.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.318-323
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• 2005

This paper introduces the mechanism of the ESD (Electrostatic discharge) in the HDD spindle system using FDBs (Fluid Dynamic Bearings). When a HDD (Hard Disk Drive) spindle system is rotating, triboelectric charging occurs in the FDBs through the friction of the lubricant between the rotating shaft and stationary sleeve. And this electrostatic charge is accumulated in the rotating part of the HDD spindle system because it is insulated from the ground by the lubricant. This research shows experimentally that the behavior of electric charge and discharge in the FDB spindle system is the same as that of a capacitor. It also measures the electrostatic charge and discharge of the FDB spindle system due to the chanse of humidity, supporting load and motor speed. This research shows that the control of ESD is required in the HDD spindle system using FDBs, because the electrostatic charge accumulated in the FDB spindle system may cause the breakdown damage of the GMR head and data loss consequently.

• 한국소음진동공학회논문집
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• 제16권1호
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• pp.75-80
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• 2006

This paper introduces the mechanism of the ESD(electrostatic discharge) in the HDD spindle system using FDBs(fluid dynamic bearings). When a HDD(hard disk drive) spindle system is rotating, triboelectric charging occurs in the FDBs through the friction between the lubricant and the rotating shaft or between the lubricant and stationary sleeve. And this electrostatic charge is accumulated in the rotating parts of the HDD spindle system because they are insulated from the ground by the lubricant. This research shows experimentally that the behavior of electric charge and discharge in the FDB spindle system is the same as that of a capacitor. It also measures the electrostatic voltage difference between the rotating and stationary parts in the FDB spindle system due to the change of humidity, supporting load and motor speed. This research shows that the control of ESD is required in the HDD spindle system using FDBs, because the electrostatic charge accumulated in the FDB spindle system may cause the breakdown damage of the GMR head and data loss consequently.