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탄소나노튜브 가스센서의 SF<sub>6</sub> 분해생성물 검출 및 확산현상에 관한 연구
이종철,정세훈,백승현,Lee, J.C.,Jung, S.H.,Baik, S.H. 한국진공학회 2009 Applied Science and Convergence Technology Vol.18 No.1
가스절연개폐장치 (Gas-insulated switchgear, GIS)의 내부에는 절연에 관한 이상 여부를 감시하고 판단할 수 있는 시스템이 요구된다. 부분방전에 의해 발생되는 $SF_6$ 분해생성물에 관한 단일벽 탄소나노튜브 (Single-walled carbon nanotube, SWNT)가 지닌 우수한 검출기능 때문에 SWNT를 이용한 가스센서 개발이 활발히 진행되고 있다. 하지만 아직까지 부분방전에 의해 발생된 분해생성물의 확산현상에 관한 해석적 연구는 미흡한 실정이다. 본 논문에서는 실험 데이터 및 상용 CFD (Computational Fluid Dynamics) 프로그램을 이용하여 SWNT 가스센서에 포획되는 분해생성물의 코로나 방전에 의한 발생 과정과 챔버 내부에서의 확산과정을 모델링하여 부분방전 발생 시 챔버 내부의 온도, 압력, 그리고 분해생성물의 농도 등을 수치계산하였다. 분해생성물의 시간당 질량생성율과 발생온도는 각각 $5.04{\times}10^{-10}$ [g/s]와 773 K이라 가정하였다. 농도방정식을 계산함에 있어 미지의 확산계수를 임의의 값으로 가정하여 직접 부여하는 방법을 사용하지 않고, 확산계수를 정의하는데 사용되는 Schmidt수의 값을 지정하여 확산계수가 $SF_6$ 가스의 물성치인 점성계수와 밀도의 함수로 계산되도록 하였다. 수치결과로부터 분해생성물의 농도구배가 확산을 일으키는데 주요 구동포텐셜 (Drive potential)이 됨을 확인하였다. 센서 설치위치가 부분방전 발생영역에서 멀리 떨어질수록 분해생성물 농도가 낮음을 알 수 있었고, 부분방전이 지속될수록 분해생성물의 농도가 증가함을 확인하였다. 다수의 센서를 챔버 내부에 설치하면 각 센서의 응답시간을 확인하여 PD 발생위치를 판단할 수 있을 것이고, 이를 통해 GIS 진단 및 유지보수에 관한 유용한 정보로 사용될 수 있을 것이다. The detection methods are required to monitor and diagnose the abnormality on the insulation condition inside a gas-insulated switchgear (GIS). Due to a good sensitivity to the products decomposed by partial discharges (PDs) in $SF_6$ gas, the development of a SWNT gas sensor is actively in progress. However, a few numerical studies on the diffusion mechanism of the $SF_6$ decomposition products by PD have been reported. In this study, we modeled $SF_6$ decomposition process in a chamber by calculating temperature, pressure and concentration of the decomposition products by using a commercial CFD program in conjunction with experimental data. It was assumed that the mass production rate and the generation temperature of the decomposition products were $5.04{\times}10^{-10}$ [g/s] and over 773 K respectively. To calculate the concentration equation, the Schmidt number was specified to get the diffusion coefficient functioned by viscosity and density of $SF_6$ gas instead rather than setting it directly. The results showed that the drive potential is governed mainly by the gradient of the decomposition concentration. A lower concentration of the decomposition products was observed as the sensors were placed more away from the discharge region. Also, the concentration increased by increasing the discharge time. By installing multiple sensors the location of PD is expected to be identified by monitoring the response time of the sensors, and the information should be very useful for the diagnosis and maintenance of GIS.
랑뮤어 탐침에 의해 변형된 열플라즈마 특성에 관한 해석적 연구
이종철,김윤제,Lee, J.C.,Kim, Y.J. 한국진공학회 2008 Applied Science and Convergence Technology Vol.17 No.3
플라즈마 진단법 중 손쉽고 구동이 용이한 장점으로 인해 범용 플라즈마 진단 장치로 사용되는 랑뮤어 (Langmuir) 탐침법은 탐침이 직접 플라즈마 내에 삽입됨으로써 플라즈마를 간섭하기 때문에 플라즈마 고유의 특성을 변형시키는 약점이 있다. 본 연구에서는 대기압 아르곤 자유 연소 아크 (free-burning arc)에 삽입된 랑뮤어 탐침에 의한 교란 영향을 고찰하기 위하여 탐침 유무에 따른 열플라즈마 상태를 수치계산 하였고, 온도장과 속도장이 왜곡된 정도를 비교 분석하였다. 열플라즈마를 모델링하기 위하여 열유동장과 전자기장에 관한 두 종류의 지배방정식을 상용 CFD 프로그램과 자체 제작한 서브루틴을 이용하여 연계 계산하였다. 삽입된 탐침에 의해 열플라즈마 온도장은 탐침의 앞뒤에서 모두 플라즈마 축의 수직 방향으로 큰 변화를 나타내는 열적 교란이 발생되었다. 속도장에서는 탐침 선단의 정체 영역과 후단 후류 영역에서 유동 교란이 발생되었으며, 삽입 된 탐침의 영향이 국부적인 것이 아닌 플라즈마 유동장 대부분 영역에 영향을 미침을 확인할 수 있었다. 따라서 탐침법의 신뢰성을 높이기 위해서는 탐침 삽입에 의한 플라즈마의 열유체역학적 교란을 고려해야 한다. Measurements with a Langmuir probe, which are the most often used procedures of plasma diagnostics, can disturb plasma flows and change its characteristics quite a little because the probe should be inserted into thermal flowing plasmas. In this study, we calculated the characteristics of thermal plasmas with and without the probe into an atmospheric argon free-burning arc numerically, and investigated aerodynamic and thermal disturbances with temperature and axial velocity distributions. For the modelling of thermal plasmas, we have made two governing equations, which are on the thermal-flow and electromagnetic fields, coupled together with a commercial CFD package and user-coded subroutines. It was found that thermal disturbances happened to both sides of the probe, before and behind, seriously. Due to the aerodynamic disturbance, we could find that there were the stagnation point in front of the probe and the wake behind it. Therefore, aerodynamic and thermal disturbances caused by the probe insertion should be considered to increase the reliability of the probe diagnostics.
이종철,김윤제,김철수,Lee, Jong C.,Kim, Youn J.,Kim, C.-S. 한국유체기계학회 2000 한국유체기계학회 논문집 Vol.3 No.3
In this study, experimental and numerical analyses are carried out to investigate the performance of centrifugal pump with various air admitting conditions. Experiments on the pump performance under air-water two-phase flow are accomplished using a centrifugal pump with semi-open type impeller having three, five and seven blades, respectively. Also, the numerical analysis of turbulent air-water two-phase flow using the finite volume method has been carried out to obtain the pressure, velocities and void fraction on the basis of a so-called bubbly flow model with the constant size and shape of cavity. The results obtained through this study show the reasonable agreements within the range of bubbly flow regime. There are promising developments concerning application of the present study for the flow in a centrifugal pump with two-phase flow conditions and efforts must be followed to improve the turbulence model and two-phase flow model for turbomachinery.
CFD코드를 이용한 SF₆ 코로나 방전 및 가스분해 모델링
이종철(J. -C. Lee),김우영(W. Y. Kim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
In this study, we modeled SF? decomposition process happened by corona discharges in a chamber and calculated temperature, pressure and concentration of decomposition products by using a commercial CFD program in conjunction with the experimental data. The results showed that the drive potential is governed mainly by the gradient of decomposition concentration. The lower concentration of decomposition products was observed as the sensors were placed more away from the discharge region. Also, the concentration was higher with the discharge time. The numerical models built through this study are expected to be applicable to developing gas sensors and various researches related to the electrical discharges.
전류용량 변화에 따른 초고압 진공차단부 온도상승에 관한 실험적 연구
이종철(J. -C. Lee),김우영(W. Y. Kim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
Nowadays, it is emphasized that the rated-current and the thermal performance should be improved together in order to satisfy the market demands on scale-down, safe function and reliability in the development of large-scale electric equipments as well as small-scale electronic devices. Due to the high complexity of heat generation and loss mechanism, it is not easy to predict the temperature-rise of switchgears under various load conditions. In this paper, we made experiments on the temperature-rise of an ultrahigh-voltage (UHV) vacuum interrupter (VI), which is the main component of vacuum switchgear, with the various rated-currents. It was found that the maximum limit of the rated-current of VI is investigated with the international standard (IEC-60943) and correlates with the electrical contact resistance between electrodes inside the vacuum bottle.
이종철(J. -C. Lee),김우영(W. Y. Kim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
In this study, we predicted the thermal breakdown of high-voltage interrupter with the characteristics of thermal plasmas such as temperature, pressure and concentration of the ablated material by using a commercial CFD program. The results showed that the pressure build-up inside the chamber was proportional to the magnitude of arcing current because the quantities of heat energy and ablated mass also increase together with the current during the compression process. And during the decompression process, the reverse flow was not coincided with the magnitude of the applied current due to the compressibility of the gas through backflow channel. The present method is expected to be useful for the design of guideline and interruption capacity on the thermal breakdown of a PASB chamber.
이종철(J. -C. Lee),김우영(W. Y. Kim) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.5
In this study, we calculated thermal plasmas happened in two types of switchgears for understanding the complex physics and the probability of thermal breakdown. The first part concerns modeling of switching arc itself with an auto-expansion chamber as an example. The second part focuses on simulation of the PTFE nozzle ablation effect by high-temperature switching arc with an puffer-assisted self-blast switchgear. The present method is expected to be useful for setting guideline of switchgear design and predicting the interruption capacity of arcing chambers.
저탄소 마르텐사이트강의 압연온도와 열처리를 통한 기계적 성질의 향상
이종철(J. C. Lee),이호진(H. J. Lee),오창석(C. S. Oh),김성준(S. J. Kim),남원종(W. J. Nam) 한국소성가공학회 2010 한국소성가공학회 학술대회 논문집 Vol.2010 No.10
There have been a number of works on manufacturing ultrafine grained steels with average ferrite grain sizes of smaller than a few micrometers to develop beneficial high strength steels. Among microstructures in low carbon steels, lath martensite is known to be useful to produce an ultrafine grained ferrite matrix and finely cementite particles. In this study, the effect of diverse deformation temperatures (Cold, Cryogenic, Warm rolling) on microstructures was investigated. And analysis of mechanical properties was used by tensile test and Vickers hardness.