• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 1993년도 추계학술발표회논문집
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• pp.58-62
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• 1993

This paper shows the discharge characteristics of liquid nitrogen under plane to plane electrode, needle to plance electrode, inserting teflon insulator in plane to plane electrode at atmospheric pressure. The main experimental device of this paper is cryostat. The important results obtained from this study are sa follows. Breakdown voltage of LN2 under N-P electrode is higher than that of under P-P electrode at atmospheric pressure. Breakdown duration time is longer with increase of electode gap under the P-P, N-P electrodes. The formation of bubbles by evaporation is observed in spite of non-applying source at atmospheric pressure and the creation of corona confirmed. Breakdown voltage and breakdown duration time are in proportion to increase of diameter in case of inserting teflon insulator. Partial discharge characteristics of thickness 0.5[mm] is that 채굼 voltage of teflon insulator rose with increase of diameter in each [pps].

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2003년도 학술대회 논문집
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• pp.291-294
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• 2003

In our newly proposed cryogenic systems for HTS transformer, liquid nitrogen is subcooled by copper sheets extended from coldhead of cryocooler. Since the shape of copper sheets has been given by the shape of HTS windings and electrical restriction, the thickness of copper sheets is the main parameter to determine operating temperature in HTS windings. Temperature distributions between windings and coldhead are investigated by heat transfer analysis, from which the thickness of copper sheets to maintain every part of windings below 66 K is calculated. The effects of the amount of AC loss on the temperature distributions in cooling system are also presented.

• 한국전기전자재료학회논문지
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• 제16권1호
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• pp.70-76
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• 2003

For the development of superconducting power apparatus, it is necessary to establish the dielectric technology in coolant like L$N_2$. Therefore in this paper we conducted experiment of surface flashover that could occur in the windings of HTS transformer which will be developed in the pancake coil type. First, we distinguished two types of surface flashover by electrode alignment, such as parallel and vertical, and then compared with each characteristics of surface flashover. The flashover voltage was more affected by thickness of spacer than by surface length when the thickness of spacer is over 1 mm. And the surface flashover with metallic particle attached on the spacer was tested, it was affected by the particle position. The more close to the electrodes, the worse the characteristics. Also the experiment was conducted when the electrode was immersed in liquid nitrogen(L$N_2$) partially. The surface flashover characteristics of spacer was, when immersed partially in 50%, rapidly decreased.

• 한국전기전자재료학회논문지
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• 제16권12S호
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• pp.1299-1304
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• 2003

Fault current limiters (FCL) are extensively needed to suppress fault currents, especially for trunk power systems heavily connected to high voltage/large current transmission lines. Due to its ideal electrical behavior, high-temperature superconductor fault current limiter (HTSFCL) becomes one of the most important developing trends of limiters in power system. This paper describes the result of an investigation of the dielectric characteristics of turn-to-turn insulation for pancake and solenoid type reactor coil in liquid nitrogen. The influence of thickness in a variety length, on AC, DC and impulse surface flashover has been investigated. Also, the relationships between the number of turn and breakdown characteristics were clarified. The information gathered in this test series should be helpful in the design of liquid nitrogen filled DC reactor type HTSFCL.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 제5회 영호남 학술대회 논문집
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• pp.3-6
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• 2003

The electrical and mechanical properties of dielectric paper and cable at cryogenic temperature have been investigated to optimum insulating design of high-Tc superconducting(HTS) cable. From the results, Tensile strength of PPLP in liquid nitrogen was high more than that of air, but tensile strain could know that decrease sharply. According as tensile strength increases, the breakdown stress of PPLP in liquid nitrogen was decreased because PPLP was degradated. According as bending radius multiple is decrese, breakdown voltage decreased sharply. And bending radius multiple is thought that more than about 25 is suitable.

• 한국대기환경학회지
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• 제6권2호
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• pp.147-154
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• 1990

A sensitive method for the determination of total selenium in aerosol particles is described. The method involves dissolution of aerosol particles by $HNO_3-HClO_4$ mixed acids, pre-reduction of Se (VI) to Se (IV) by boiling hydrochloric acid, and hydride generation followed by atomic absorption detection. Dissolved Se (IV) in 4M hydrochloric acid is reacted with $NaBH_4$ to form $H_2Se$, which is subsequently collected in an U-tube cooled in liquid nitrogen. Upon the completion of $H_2Se$ generation, the collected $H_2Se$ is rapidly vaporized into a quartz cuvette burner by removing the U-tube from liquid nitrogen, atomized, and then detected by an atomic absorption spectrophotometer. The absolute sensitivity of the method is 0.49 ng/0.0044 Abs. The accuracy of the method evaluated by analyzing standard reference materials for urban aerosol is better than 10%. Analytical results for urban and rural aerosol particles are reported.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 춘계학술대회 논문집 초전도 자성체 연구회
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• pp.61-64
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• 2003

The degradation of the dielectric properties of insulating papers that were used under loaded conditions at cryogenic temperature was paid attention. Electrical and tensile stress properties of dielectric paper at cryogenic temperature have been investigated to optimum insulating design of high-Tc superconducting(HTS) cable. Tensile strength of PPLP in liquid nitrogen was high more than that of air, but tensile strain could know that decrease sharply. According as tensile strength increases, the breakdown stress of PPLP in liquid nitrogen was decreased.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제35회 추계학술대회논문집
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• pp.597-600
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• 2010

극저온 액체 질소 제트 유동의 아임계 및 초임계 특성을 파악하기 위한 실험을 수행하였다. 단일 제트 분사기를 고압 챔버 내에 장착하여 제트의 주위기체압력, 분사기 형상 및 유동 조건의 영향을 조사하였다. 실험 결과로부터 아임계 조건과 초임계 조건에서의 제트의 특성 변화를 관찰하였으며, 주위기체압력이 대기압일 경우 유동 내에 섭동이 발생함을 파악하였다. 분사기 형상에 따른 유동 변화 또한 파악하였다.

• 대한안전경영과학회지
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• 제4권2호
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• pp.223-235
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• 2002

This paper presents some indirect physical evidences indicating that reduced friction occurs in an economical cryogenic machining process, in which LN2 is applied selectively in well-controlled jets to the localized cutting zone. These evidences include cutting force components, tool wear rate and chip morphology. LN2 reduced the tool wear rate to a great extent and elongated the tool life up to four times compared to emulsion cooling. The friction reduction was further reflected in larger shear angle and less secondary deformation in the chip microstructures. This study also found that the effectiveness of LN2 lubrication depends on the approach how LN2 is applied.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.709-712
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• 2017

극저온 액체 질소가 초임계 상태에서 분사될 때 역광기법(backlight method)을 이용하여 사진을 얻었다. 이 때, 유체의 온도를 함께 측정하였고, 이를 바탕으로 가짜 감압비등이라는 새로운 분열기구를 제안하고자 하였으나, 역광기법은 정성적인 분무의 외관은 보여주지만 분사되는 유체의 큰 밀도로 인하여 밀도 변화를 보여줄 수 없었다.