• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 하계학술대회 논문집 Vol.7
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• pp.257-258
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• 2006

The $I_c$ degradation behaviors of externally-reinforced Bi-2223 superconducting tapes under pressurized liquid nitrogen were investigated. Tapes with different thickness of reinforcement layers were compared and the results showed that when the bending strain was calculated at the outer surface, the tape with the thicker reinforcement showed a better bending strain tolerance of $I_c$, but when the bending strain was calculated at the outermost filament, the $I_c$ degradation behavior became identical for all tapes. $I_{c0}$ decreased with the increase of applied pressure. After depressurization to atmospheric pressure from 1 MPa, the $I_c$ was completely recovered to its initial values. Ballooning occurred after a thermal cycle.

• 한국초전도ㆍ저온공학회논문지
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• 제23권4호
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• pp.35-38
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• 2021

Conventional direct current (DC) rotating machines are usually used for crane and press machine using high torque in metal and steel industries, because of a constant output power along variable rotating speed. A general DC motor with permanent field magnets could not increase a magnetic flux density at a gap between armature coils and field magnets. However, a superconducting DC motor has field magnets composed with high temperature superconducting (HTS) coils and it could increase the magnetic flux density at the gap to over 10 times than those of a general DC motor by control the excitation current into HTS coils. The superconducting DC motor could be operated with extremely high torque and constant output power at a low rotational speed. In this paper, a 500 W superconducting DC rotating machine was conceptually designed with a LN₂ (Liquid Nitrogen) cooling method and the operation characteristics results of HTS field magnets were presented. The two no-insulation HTS magnets for a 500 W superconducting DC rotating machine were fabricated. The excitation current for the HTS magnets could be controlled from 0 to 40 A. This test results will be available to design large-sized HTS magnets for a number of hundred kW class superconducting DC rotating machine under LN₂ cooling system.

• 한국가축번식학회지
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• 제12권2호
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• pp.77-83
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• 1988

This study was done with mouse embryo to assess effects of freezing media containing sucrose, freezing metods(1-F, 0.3$^{\circ}C$/min;2-F, 3-5$^{\circ}C$/min;3-F, 15$^{\circ}C$min;4-F, LN2 vapour) and cell freezers on the embryo survival determined using the FDA test. The results are summarized as follows. 1. The FDA score obtained with 1, 2, 3 and 4-F was 3.8, 3.6, 3.2 and 3.2, respectively. There was a significant difference(P<0.05) between 1-F, 3-F and 2-F, 4-F. 2. The score at the morular stage(3.8) higher(P<0.005) than the blastocyst stage of embryos(3.2). 3. No difference (P>0.05) was found between the score obtained with a automatic embryo freezer(4.0) and a liquid nitrogen container(3.7).

• 한국터널지하공간학회 논문집
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• 제16권5호
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• pp.431-443
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• 2014

본 연구는 고수압 해저터널의 차수를 위한 동결공법 적용성 평가를 위해 국내 적용사례가 없는 동결공법의 해외 시공사례를 조사하였으며, 지반 동결공법에서 보편적으로 사용하는 냉매인 브라인(brine)과 액체질소($LN_2$)에 대한 분석을 수행하였다. 고수압 조건의 해수는 순수한 물에 비하여 어는 점이 더 낮기 때문에 지상에서보다 동결시간이 더 길 수 있고 해저터널과 같이 폐쇄된 공간에서의 적용 시 냉매는 안정성을 확보할 수 있어야 하고 공기 단축이 가능해야 한다. 브라인은 재사용이 가능하고 독성이 적어 인체에 미치는 영향이 적으나, 동결에 상대적으로 장시간 필요하고 동결장비가 복잡한 특징을 가지고 있으며, 액체질소는 냉매의 재사용이 불가하며 기화 시 공기 중 질소농도 증가로 질식의 위험성이 있으나, 상대적으로 동결시간이 짧으며, 동결장비가 간단한 특징을 가지고 있는 것으로 파악되었다. 또한 향후 추가적인 연구가 필요한 해저터널 연결구 및 막장면 주변 지반에 대한 동결공법의 주요 설계요소를 도출하였다.

• 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.

• 한국수소및신에너지학회논문집
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• 제34권5호
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• pp.526-534
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• 2023

To evaluate the risk of leakage when using liquid hydrogen, a leakage test was conducted using liquid nitrogen in an outdoor environment rather than a laboratory environment. To assume a real-scale continuous leak, liquid nitrogen was allowed to leak for 5 minutes through a pipe with a diameter of 25.4 mm at a design spill rate of 60 L/min. The measurement system consisted of devices for climate conditions, LN2 spread and vapor clouds. The main experimental results are the liquid pool radius and the concentration of vapor cloud, and the radius of the liquid pool was compared with the numerical analysis results.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
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• pp.7-11
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• 1999

The recent progress in new cooling techniques of the high Tc superconductor(HTS) systems is reported and discussed with some practical examples. At the beginning stage of the HTS development in research laboratories, liquid nitrogen(LN$_2$) is the standard medium for an effective cooling. The success of HTS in many different application areas, however, has required a variety of need in the cooling temperature and the cooling capacity with specific design restrictions. While the utilization of alternative liquid cryogens such as liquid neon (LNe) or liquid hydrogen (LH$_2$) has been tired in some of them, even solid cryogens such as solid nitrogen (SN$_2$) or solid hydrogen (SH$_2$) may be another option in special applications. The gaseous helium cooled by a cryogenic refrigerator has also been a good candidate in many cases. One of the best cooling methods for the HTS is the direct conduction-cooling by a closed-cycle refrigerator with no cryogen at all. The refrigeration may be based on Joul-Thomson, Brayton, Stirling, Gifford-McMahon, or pulse tube cycles. The pros and cons of the newly proposed cooling methods are described and some significant design issues are presented.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제48권9호
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• pp.648-655
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• 1999

In this study, a relationship between DC discharge and the radiated electromagnetic waves is investigated by measuring electromagnetic waves using a biconical antenna and a spectrum analyzer. The characteristics of frequency spectrum ofthe radiated electromagnetic waves was measured at the atmospheric pressure in Liquid Nitrogen $(LN_2)$ during partial discharges in nonuniform and uniform electric field depend on positive DC power. From this experiment results, it was confirmed that when partial discharge was produced in Liquid Nitrogen and Air, the signal of partial discharge was detected by this experiment and the analysis method. It is considered thatthese results obtained from this investigation may be used as fundamental data for diagnosis and prediction of insulation on the equipments ultra-high voltage, superconducting and cryogenic applications.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 C
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• pp.1975-1977
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• 2000

In this study, a relationship between AC discharge progress and the radiated electromagnetic waves were investigated by measuring electromagnetic waves using a biconical antenna and a spectrum analyzer. The characteristics of frequency spectrum of the radiated electromagnetic waves was measured at the atmospheric pressure in liquid nitrogen($LN_2$) during partial discharges progress in nonuniform electric field depend on AC power supply. From this results, it was confirmed that when partial discharge was produced in liquid nitrogen, the signal of partial discharge was detected by frequency spectrum of the radiated electromagnetic waves. It is considered that these results obtained from this investigation may be used as fundamental data for diagnosis and prediction of insulation on superconducting and cryogenic power equipments.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 추계학술대회 논문집 학회본부 C
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• pp.956-958
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• 1998

In this study, a relationship between partial discharge and the radiated electromagnetic waves is investigated by measuring electromagnetic waves using a biconical antenna and a spectrum analyzer. The patterns of frequency spectrum of radiated electromagnetic waves measured at the atmospheric pressure in Liquid Nitrogen($LN_2$) during the partial discharges in nonuniform electric field depend on positive DC power. From these points of view. it is considered that these results obtained from this investigation may be used as fundamental data for diagnosis and prediction of insulation on the equipments of superconducting and cryogenic applications.