• Progress in Superconductivity and Cryogenics
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• v.12 no.1
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• pp.22-27
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• 2010

This paper analyzed bus voltage sag caused by recloser-fuse coordination in a power distribution system with SFCL. Generally, the recloser is installed to upstream of fuse to clear against both permanent and temporary faults appropriately, when the fault happened and to block expansion of the fault area. Furthermore, when the fault occurred, bus voltage sag is caused by increased fault currents. However, in a power distribution system with SFCL, the fault current could be decreased by the effect of the impedance value of the SFCL and place to install one as long as it could improve bus voltage sag. Therefore, to analyze the effect of the improvement of bus voltage sag caused by recloser-fuse coordination in a power distribution system with SFCL, we used PSCAD/EMTDC about a permanent fault at the place behind the fuse.

• Proceedings of the Korea Information Processing Society Conference
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• 2022.11a
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• pp.188-190
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• 2022

본 연구에서는 정전류(Constant Current) 방식에 전압강하법을 이용하여 접촉저항 측정 시스템을 구현하고 측정값을 블루투스 통신을 통해 안드로이드 운영체제에서 확인할 수 있도록 앱을 개발한다. 측정가능한 범위로 0 Ω에서 10.24 Ω 사이의 접촉 저항을 MCP3424 18 bit 분해능 ADC를 사용하여 측정할 수 있도록 설계하였다. 기존에는 반고정 저항과 별도의 전류계를 이용하여 정전류를 설정하였으나, 본 연구에서는 측정의 정밀도 및 편리성 개선을 위해 0.1% 고정밀 고정저항을 병렬로 4개 연결하여 구현하였으며, 또한 1:1 Unity Gain Buffer를 구성하고 Ultra High Precision Z-Foil 방식으로 오차 0.01%, 온도 계수 0.05 ppm/℃ 저항을 사용하여 실제로 측정한 샘플 저항 값의 결과를 확인하였다.

• Journal of the Korean Electrochemical Society
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• v.12 no.4
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• pp.342-348
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• 2009

Zn/Air secondary batteries are high energy density type and environment-friendly. Also, they have safer properties than batteries of other type by low manufacturing cost and using the electrolyte solution. But, they have a weak concerning large output discharge. Oxygen evolution reaction(OER) and oxgen reduction reaction(ORR) in aqueous solution make a result of a decrease of cell efficiency and life span. Therefore, to minimize the voltage drop from between OCV and charge/discharge voltage is key point. The problem should be solved through developing catalysts of high efficiency. In this study, we synthesized $Pr_{1-x}(Sr,\;Ca)_x\;CoO_3$ powders by citric method and then measured physical characteristics of each powder by XRD, SEM, TGA etc. We examined its electrochemical properties by the cathodic polarization, anodic polarization and cyclic voltammogram. We achieved results that new catalysts showed better performances than existing $La_{1-x}Sr_xCoO_3$, $La_{1-x}Ca_xCoO_3$, ect. catalysts prepared in our lab.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.19 no.1
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• pp.203-209
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• 2019

In this work, a new land-specific resistance measuring device (GM) and a measuring probe (Grounding Rod) are connected to the WENNER quadrant as power-line communication (PLC). In groups of two (P1,P2) probes, five to ten probes are installed in series on the ground at intervals of 1m, 2m, 4m, 8m, and 16m, respectively. If the PLC signal from the GMD is detected by the receiver of the Probe 1 (P1) for measurement, the minute voltage and current for measurement flow from the PSD (power supply) attached to the probe to the ground, and then, through the soil between P1 and P2, enters the Probe 1 (P2). The resistance value is then measured by the principle of voltage drop due to ground resistance. Measure the earth resistance every T seconds up to 1 trillion and store the measured data on the Arduino Server mounted on the main equipment. Stored measurement data can be derived from formulas by Ohm's Law and from inherent resistance (here,). Data obtained in real time will be linked to CDGES programs installed on Main PC, enabling data analysis and real-time monitoring of the ground environment on land. In addition, a three-dimensional display is possible with 3D graph support by identifying seasonal characteristics such as temperature and humidity of land (soils). The limitations of the study will require specific application measures of Test Bed for commercial access to a model that has been developed and operated experimentally.

• Journal of the Korean Vacuum Society
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• v.7 no.3
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• pp.195-200
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• 1998

We have investigated the crystal structure and electrical properties of Pt/SBT/$CeO_2$/Si(MFIS) and Pt/SBT/Si(MFS) structures for the gate oxide of ferroelectric memory. XRD spectra and SEM showed that the SBT film of SBT/$CeO_2$/Si structure had larger grain than that of SBT/Si structure. Furthermore HRTEM showed that SBT/$CeO_2$/Si had 5 nm thick $SiO_2$layer and very smooth interface but SBT/Si had 6nm thick $SiO_2$layer and 7nm thick amorphous intermediate interface. Therefore, $CeO_2$film between SBT film and Si substrate is confirmed as a good candidate for a diffusion barrier. The remanent polarization decreased and coercive voltage increased in Pt/SBT/$CeO_2/Pt/SiO_2$/Si structure. This effect may increase memory window of MFIS structure directly related to the coercive voltage. From the capacitance-voltage characteristics, the memory of Pt/SBT(140 nm)/$CeO_2$(25 nm)/Si structure were in the range of 1~2 V at the applied voltage of 4~6 V. The memory window increased with the thickness of SBT film. These results may be due to voltage applied at SBT films. The leakage currents of Pt/SBT/$CeO_2$/Si and Pt/SBT/Si were $ 10^8A/\textrm{cm}^2$ and $ 10^6 A/\textrm{cm}^2$, respectively.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.9
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• pp.144-155
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• 2013

This paper presents a low-cost remote power-quality-failure monitoring system (RPMS) using Android App and TI MCU (micro-controller unit), which is appliable to a micro-grid. The designed RPMS testbed consists of smart nodes, a server, and Android APPs. Especially, the C2000-series MCU-based RPMS smart node that is low-cost compared to existing monitoring systems has both a signal processing function for power signal processing and a data transmission function for power-quality monitoring data transmission. The signal processing function implements both a wavelet-based power failure detection algorithm including sag, swell, and interruption, and a FFT-based power failure detection algorithm including harmonics such that reliable and real-time power quality monitoring is guaranteed. The data transmission function implements a low-complexity RPMS transmission protocol and defines a simple data format (msg_Diag) for power monitoring message transmission. We may watch the monitoring data in real time both at a server and Android phone Apps connected to the WiFi network (or WAN). We use RS-232 (or Bluetooth) as the wired (or wireless) communication media between a server and nodes. We program the RPMS power-quality-failure monitoring algorithm using C language in the CCS (Code Composer Studio) 3.3 environment.

• 한국신재생에너지학회:학술대회논문집
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• 2009.11a
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• pp.131-131
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• 2009

최근 환경규제가 강화되면서 친환경적인 전력생산 요구 등의 외부환경 변화에 따른 우리나라의 전력구조가 기존의 중압 집중형 발전을 탈피한 분산전원 발전에 대한 관심이 증대되고 있는 실정이다. 특히, 분산전원으로서의 전력생산은 공급의 안전성, 경쟁력 및 에너지의 지속성 등이 요구되어지는데, 재생에너지가 가지고 있는 에너지 지속성의 한계 및 설치의 제약성을 탈피할 수 있는 시스템으로 현재 연료전지시스템이 가장 근접해 있는 실정이다. 즉, 도시가스 인프라가 우수하고 인구조밀 지역이 많은 우리나라의 특성상 각 가정 및 건물에 쉽게 설치하고 공급의 안전성을 갖는 건물용 연료전지는 최근 가장 각광받고 있는 분산전원 시스템 중의 하나이다. 올해부터 모니터링사업의 일환으로 수용가에 설치 될 연료전지 시스템이 얼마나 안정적으로 전기와 열을 각 가정에 공급하고 시스템의 안전성을 확보하는 가는 건물용 연료전지의 분산전원으로서의 가능성 및 국민의 수용성을 증대시키는 중요한 역할을 할 것이다. 연료전지시스템은 상용전력과 연계되어 있기 때문에 시스템의 안정성 뿐만 아니라 상용전력의 변화에 대응하여 안정적인 운전을 하는지에 대한 평가가 필수적이다. 이에 따라 본 연구에서는 가정용 연료전지시스템의 성능 및 안전성평가의 일환으로 계통연계형 전력변환장치의 성능 및 안전성을 평가 하고자 한다. 연료전지 검사를 위한 계통연계형 전력변환장치의 시험평가 항목으로는 크게 정상특성성능시험, 보호기능성능시험, 과도응답특성성능시험 및 외부사고성능시험 등으로 나뉘어진다. 본 연구에서는 외부사고 성능시험 항목들인 출력측 단락시험, 계통전압 순간정전?순간강하시험 및 부하차단 시험 등을 통하여 외부사고에 대한 성능 및 안전성을 평가하였다. 외부사고 성능시험의 주 목적은 시스템의 이상 운전이 아니라 외부의 영향에 따른 시스템의 안전성 및 전력품질을 평가한다. 출력측 단락시험을 수행하기 위해서 전력변환장치를 정격 출력 전압, 정격 출력 주파수 및 정격 출력에서 운전한 후, 교류 전원장치는 단락 전류를 검출하여, 사고 발생 후 0.3초 이내에 개방하도록 설정하였다. 여기서, 단락 저항 Rsc를 정격 전류의 10배 이상에 해당하는 부하와 같은 값으로 설정하였다. 스위치 SWSC를 폐로하여 단락 상태를 만들며, 이 때 전력변환장치의 출력전류와 차단 또는 정지 시간을 측정하였다. 실험 결과에 대한 판정기준은 단락전류를 검출하여 0.5초 이내에 개폐기 개방 또는 게이트 블록 기능이 동작하여 시스템을 안정하게 정지시키고 시스템 어떤 부위에도 손상이 없어야 한다. 실험 결과 파워컨디셔너의 출력전류 및 차단 또는 정지된시간이 40ms로 나타났고, 출력전류의 파형도 매우 안정함을 볼 수 있었다. 이와 같이 모든 실험을 수행한 결과 외부사고에 대하여 시스템이 안전하게 정지하는 등 연료전지 시스템의 안전성을 확인하였다.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.2 no.1
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• pp.3-9
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• 2009

Although Active matrix organic light emitting diode (AMOLED) display has a better image quality in terms of viewing angle, contrast ratio, and response time than liquid crystal displays (LCDs), it still has some critical issues such as lifetime, residual images, and brightness non-uniformity due to non-uniformity in electrical characteristics of driving TFTs and IR drops on supplied power line. Among them, we improved irrecoverable residual images of AMOLED displays which is mainly related to the hysteresis characteristics of driving TFTs. We consider four kinds of surface treatment conditions before gate oxide deposition for improving hysteresis characteristics. We can reduce the hysteresis level of p-channel TFT to 0.23 V, interface trap states between the poly-Si layer and gate insulator to $3.11{\times}10^{11}cm^{-2}$, and output current variation of p-channel TFT to 3.65 % through the surface treatment using ultraviolet light and H2 plasma. Therefore, the recoverable residual image problem of AMOLED displays can be improved by surface treatment using ultraviolet light and $H_2$ plasma.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.8
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• pp.706-713
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• 2007

The jet structure issuing from a conventional convergent nozzle of variable expansion rate is compared with the result from the nozzle of a constant expansion rate using a normal type annular slit. In experiments, to investigate the jet characteristics between the two cases of jet, the mean velocity of nozzle exit is fixed to be 90m/s, the pressures along the jet axis and radial directions are measured by a scanning valve system moving with 3-axis auto-traverse unit, and the velocity distribution obtained by calculation from the measured static and total pressures is compared. Also to obtain the highly stable and convergence jets, it is turned out that the flow through a nozzle of constant expansion rate using the Coanda effect with an annular slit is the most preferable than that case through variable expansion rate nozzle. Furthermore, it is found that the pressure drop along the nozzle for the constant expansion rate nozzle is small relatively against to the case of variable expansion rate nozzle.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.6 no.3
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• pp.168-173
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• 2013

In this paper, we tried different two approach to improve the performance of the IGBT. The first approach is that adding N+ region beside P-base in the conventional IGBT. It can make the conventional IGBT to get faster turn-off time and lower conduction loss. The second approach is that adding P+ region on right side under gate to improve latching current of conventional IGBT. The device simulation results show improved on-state, latch-up and switching characteristics in each structure. The first one was presented lower voltage drop(3.08V) and faster turn-off time(3.4us) than that of conventional one(3.66V/3.65us). Also, second structure has higher latching current(369A/?? ) that of conventional structure. Finally, we present a novel IGBT combined the first approach with second one for improved trade-off characteristic between conduction and turn-off losses. The proposed device has better performance than conventional IGBT.