• 비파괴검사학회지
• /
• 제30권5호
• /
• pp.479-483
• /
• 2010

초저온 액화가스인 LNG의 저장탱크에 사용되는 9% 니켈강은 Inconel 혹은 Hastelloy 계열 용접봉을 사용하여 용접되며, 용접부는 저합금강과 오스테나이트 스테인리스강의 이종금속 용접부와 유사한 특성을 가지고 있다. 용접부에 대한 방사선투과시험 시 용접조건에 따라 밴드형태의 지시가 방사선투과 필름 상에 나타나곤 한다. 따라서 본 연구에서는 이에 대한 해석을 위하여 재료, 방사선투과시험, 초음파탐상시험, 액체침투탐상시험 및 조직시험을 통하여 의사지시 여부를 확인하였으며, 방사선투과시험 해석 및 밴드형태 지시의 발생 원인을 제시하였다.

• 한국초전도ㆍ저온공학회논문지
• /
• 제15권2호
• /
• pp.1-8
• /
• 2013

This paper reviews the development status of magnetic refrigeration system for hydrogen liquefaction. There is no doubt that hydrogen is one of most important energy sources in the near future. In particular, liquid hydrogen can be utilized for infrastructure construction consisting of storage and transportation. Liquid hydrogen is in cryogenic temperatures and therefore high efficient liquefaction method must be studied. Magnetic refrigeration which uses the magneto-caloric effect has potential to realize not only the higher liquefaction efficiency > 50 %, but also to be environmentally friendly and cost effective. Our hydrogen magnetic refrigeration system consists of Carnot cycle for liquefaction stage and AMR (active magnetic regenerator) cycle for precooling stages. For the Carnot cycle, we develop the high efficient system > 80 % liquefaction efficiency by using the heat pipe. For the AMR cycle, we studied two kinds of displacer systems, which transferred the working fluid. We confirmed the AMR effect with the cooling temperature span of 12 K for 1.8 T of the magnetic field and 6 second of the cycle. By using the simulation, we estimate the total efficiency of the hydrogen liquefaction plant for 10 kg/day. A FOM of 0.47 is obtained in the magnetic refrigeration system operation temperature between 20 K and 77 K including LN2 work input.

• 조명전기설비학회논문지
• /
• 제21권4호
• /
• pp.115-121
• /
• 2007

This paper describes experiments of the breakdown characteristics by temperature change of $SF_6$ gas and Imitation Air(I-Air) in model GIS(Gas Insulated Switchgear). From the results of the experiments, the breakdown characteristics classify the vapor stage of $SF_6$ according to Paschen's law, in which the stage of coexistence for gas & liquid of the voltage value increases. This results in large deviation and the breakdown of the voltage(VB) low stage as the interior of the chamber is filled with a mixture of $SF_6$ that is not liquefacted and remaining air that can not be ventilated. The ability of $SF_6$ liquid($LSF_6$) insulation is higher than high-pressurize $SF_6$ gas. The VB of the I-Air decreases as the temperature drops and the VB also drops. It is considered that the results of this paper are fundamental data for the electric insulation design of superconductor and cryogenic equipment that will be studied and developed in the future.

• ALGAE
• /
• 제18권4호
• /
• pp.321-331
• /
• 2003

Cryopreservation of sporothalli of the red alga Porphyra (P. seriata, P. yezoensis, P. tenera, P. pseudolinearis and P. dentata) was performed by the two-step cooling method in liquid nitrogen. The algal samples were suspended in various cryoprotective solutions, and slowly cooled to -40$^{\circ}C$ in 4 hours using a programmed freezer. After the first slow cooling the suspensions with cryoprotectants were immediately immersed in liquid nitrogen. The suspension from the programmed freezer was thawed quickly by agitation of the vial in a water bath at 40°C. When ice in the suspension of cryogenic vial was mostly melted, the vial was transferred to an ice bath for complete melting of the residual ice. The cryoprotectants in the vial were washed off by gradual dilution with seawater. The viability of the cell was assessed with neutral red staining. The viability of Porphyra samples ranged 54.6-70.9% when the mixed suspension of 10% dimethylsulfoxide and 0.5 M sorbitol in 50% seawater used as a cryoprotectant.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1998년도 하계학술대회 논문집 E
• /
• pp.1699-1701
• /
• 1998

This paper was studied on the surface discharge characteristics on the solid insulators in the Liquid Nitrogen($LN_2$) at atmospheric pressure. Liquid Nitrogen has been widely used as a tooling and insulating materials for superconducting and cryogenic cable. Considering the effect of bubbles, we observed tracking Phenomena on the surface of solid insulators and investigated surface breakdown characteristics of several solid insulators.

• 대한전기학회논문지:전기물성ㆍ응용부문C
• /
• 제54권8호
• /
• pp.355-360
• /
• 2005

In this paper the experiments of breakdown characteristics by temperature change of $SF_6$ gas, $SF_6$ liquid ($LSF_6$) and $N_2$ liquid ($LN_2$) in model GIS(Gas Insulated Switchgear) were described. From the experiments results, the breakdown voltage of $SF_6$ increases with the drop of temperature and the increase of the inner pressure in model GIS. The ability of $LSF_6$ insulation is higher than high-pressurized $SF_6$ gas and $LN_2$. The breakdown characteristics of $LSF_6$ were produced by bubble formed evaporation of $LSF_6$ and bubble caused by high electric emission. It is considered in this paper that the results are fundamental data for electric insulation design of superconductor and cryogenic equipments machine교 which will be studied and developed in the future.

• 한국초전도ㆍ저온공학회논문지
• /
• 제7권3호
• /
• pp.39-42
• /
• 2005

In this paper, the thermal characteristics of multilayer insulation (MLI) were experimentally investigated by using boil-off calorimetry method for seeking optimum standards of thermal insulation conditions. It is necessary to design the thermal insulating efficiency for applying to cryogenic instruments such as HTS power cable system. It is well known that the thermal characteristics and heat transfer of MLI are greatly affected by various MLI structures such as the number of layers and layer density, etc. However, it is difficult to know the thermal characteristics of MLI correctly. The heat leak by MLI between room temperature and liquid nitrogen temperature was measured at various conditions using a cylindrical cryostat. The cryostat consists of two guard vessels located at both end sides and a test vessel between them. The guard vessels are also filled with liquid nitrogen to prevent radiation heat leak through the both end side of the cylindrical test vessel to measure the heat leak only through MLI.

• 한국조명전기설비학회:학술대회논문집
• /
• 한국조명전기설비학회 2009년도 춘계학술대회 논문집
• /
• pp.267-269
• /
• 2009

In this paper, insulations characteristics by temperature changes($+10{\sim}-60[^{\circ}C]$) of $SF_6$ 9as in the experimental chamber were studied. From this result, The breakdown characteristics classify the gas & liquid coexisted stage of voltage value increases & much deviation and the $V_B$ low stage as the interior of chamber gets filled with mixture of $SF_6$ that are not liquefacted and remaining air which couldn't be ventilated. In addition the ability of insulation of liquid $SF_6$ was higher than that of the highly pressurized $SF_6$ gas. In this research, we want to provide the base data on designing insulation of high-temperature superconductor and the cryogenic equipments by investigating the insulation characteristics of $SF_6$.

• Journal of Electrical Engineering and Technology
• /
• 제2권2호
• /
• pp.257-262
• /
• 2007

In this paper the experiments of breakdown characteristics by temperature change of $SF_6$ gas($GSF_6$), and $SF_6$ liquid ($LSF_6$) in model GIS (Gas Insulated Switchgear) are described. From the experiment's results, the breakdown characteristics classify the vapor stage of $SF_6$ according to Paschen's law, in which the gas & liquid coexisted stage of voltage value increases, resulting in much deviation and the breakdown of voltage ($V_B$) low stage as the interior of the chamber gets filled with a mixture of $SF_6$ that is not liquefacted and remaining air that cannot be ventilated. The ability of $LSF_6$ insulation is higher than the high-pressurized $SF_6$ gas. The breakdown characteristics of $LSF_6$ were produced by bubble formed evaporation of $LSF_6$ and bubbles caused by high electric emission. It is considered in this paper that the results are fundamental data for electric insulation design of superconductor and cryogenic equipments machinery that will be studied and developed in the future.

• 한국초전도ㆍ저온공학회논문지
• /
• 제12권1호
• /
• pp.61-65
• /
• 2010

To develop the thermal analysis method for the thermal behavior of HTS power cable system, cooled with sub-cooled liquid nitrogen, new thermo dynamic model for HTS cable system is introduced. The introduced thermal model is mainly modified from the thermal circuit following to IEC60287 for underground power cable systems such as XLPE or paper wrapped insulation cables. The thermal circuits for HTS cables are similar to the forced cooled underground cable system but the major thermal parameters and the configuration is apparently different to the normal cable systems so there has been no proposals in this field of analysing method. In this paper, 154kV HTS cable system has been introduced as an aspects of thermal models and a thermal circuit is proposed for the fundamentals on the dynamic rating systems for the HTS cable system. By using the thermal circuit developed in this paper, the optimal controls on the sub-cooling system's capacity become possible and it is expected to make the efficiency of HTS cable higher than conventional static controls.