• 한국품질경영학회:학술대회논문집
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• 한국품질경영학회 1998년도 The 12th Asia Quality Management Symposium* Total Quality Management for Restoring Competitiveness
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• pp.680-695
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• 1998

The objective of this study is to optimize the responses of the creep feed ceramic grinding process simultaneously by an off-1ine multicriteria optimization methodology. The responses considered as objectives are material removal rate, flexural strength, normal grinding force, workpiece surface roughness and grinder power. Alumina material was ground by the creep feed grinding mode using superabrasive grinding wheels. The process variables optimized for the above objectives include grinding wheel specification, such as bond type, mesh size, and grit concentration, and grinding process parameters, such as depth of cut and feed rate. A weighting method transforms the multi-objective problem into a single-objective programming format and then, by parametric variation of weights, the set of non-dominated optimum solutions are obtained. Finally, the multi-objective optimization methodology was tested by a sensitivity analysis to check the stability of the model.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.109-110
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• 2008

전체송전용량은 열 안정도, 과도안정도, 전압안정도 등에 의하여 제한을 받게 되는데, 한전 전력시스템에서는 주로 전압안정도에 의하여 제한을 받는다. 현재에도 상당한 규모로 북상조류가 흐르고 있어서, 전력시스템의 안정도를 고려한 융통전력의 한계가 중요한 문제로 부각되고 있다. 본 논문에서는 평가선로 조류의 모선 전력 민감도를 활용하여 전체송전용량을 산정하는 기법이 IEEE 39 모선 테스트 시스템에 적용되며, 실제적으로 운용하고 있는 경제급전의 순서인 Merit order(우선 순위)를 적용하여 전체송전용량 산정을 하는 것과의 결과를 비교 검토한다.

• 한국전자파학회논문지
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• 제9권2호
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• pp.219-225
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• 1998

A voltage controlled oscillator for the local oscillator in 380 MHz TRS handset is designed and fabricated. To improve the phase noise characteristics, the NEC's 2SC4226 transistor with NF=1.2 at 1 GHz and Toshiba's 1SV229 varactor diode with Q=70 are used. And an inductor of VCO is realized by microstrip line. At the bias condition of 5 V and 10 mA, the output power and phase noise in the operating frequency range of 357∼387 MHz are above 3.7 dBm and 111 dBc/Hz at 12.5KHz offset from the carrier, respectively. And FM sensitivity deviation are within ±0.4 KHz. This VCO is well suited for TRS handset.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1995년도 하계학술대회 논문집 B
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• pp.556-558
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• 1995

This paper presents a new simplified method for finding the multiple load flow solutions and through their solutions the voltage stability can be evaluated. Line flow($P_{ij}$, $Q_{ij}$) may be formulated with the second-order equations for $V_{i}^{2}$ in polar coordinates or two circle equations for $e_{i}$ and $f_{i}$ in rectangular coordinates. Based on this feature, multiple load flow solutions are calculated with simple works, results of multiple load flow solutions are used for sensitivity analysis of voltage stability. Also, in the case that reactive power sources is considered, method of evaluating the voltage stability is introduced. The proposed method was validated to 2-bus and IEEE 6-bus system.

• 천문학논총
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• 제14권1호
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• pp.39-45
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• 1999

We have carried out measurements of 1.2-1.6GHz radio interferences around Seoul Radio Astronomy Observatory located in the campus of Seoul National University. We received interference signals using a pyramidal horn antenna and measured its power using a spectrum analyzer with 1MHz resolution after $\~60dB$ amplification. In order to check the spatial characteristics, we made observations at every $30^{\circ}$ in azimuth at elevation of $30^{\circ}\;and\;60^{\circ}$. Also, in order to check the temporal characteristics, we repeated the all-sky observations five times at every six hours. The results may be summarized as follows: (1) There are strong $({\geq}-20dBm)$ interferences between 1.2 and 1.4GHz. Particularly strong interferences are observed at 1.271 and 1.281GHz, which have maximum powers of -0.34dBm and -0.56dBm, respectively. (2) The characteristics of the interferences do not depend strongly on directions, although the interferences are in general weak at high elevation and in east-west direction. (3) The interferences appear for a very short $(\leq0.01s)$ period of time, so that the average power is much smaller than the maximum power. Strong interferences with large $(\leq-49.0dBm)$ average power have been observed at 1.271, 1.281, 1.339, and 1.576GHz. At these frequencies, the interferences appear repeatedly with a period of $\leq0.1s$ By analyzing the observed power, we find that, for the strongest 1.271GHz interference, the average intensity is $-171dBW/m^2/Hz$ and that the maximum intensity is $-122dBW/m^2/Hz$. If this interference is delivered to the detector without any shielding, then its power would be much greater than the rms noise of a typical line spectrum. Therefore, it is important to shield all the parts of receiver carefully from radio interferences. Also, without appropriate shielding, the sensitivity of a receiver could be limited by the interference.

• Journal of Electrical Engineering and Technology
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• 제13권4호
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• pp.1459-1473
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• 2018

This paper focuses on voltage control schemes for multi-terminal low-voltage direct current (LVDC) distribution systems. In a multi-terminal LVDC distribution system, there can be multiple AC/DC converters that connect the LVDC distribution system to the AC grids. This configuration can provide enhanced reliability, grid-supporting functionality, and higher efficiency. The main applications of multi-terminal LVDC distribution systems include flexible power exchange between multiple power grids and integration of distributed energy resources (DERs) using DC voltages such as photovoltaics (PVs) and battery energy storage systems (BESSs). In multi-terminal LVDC distribution systems, voltage regulation is one of the most important issues for maintaining the electric power balance between demand and supply and providing high power quality to end customers. This paper focuses on a voltage control method for multi-terminal LVDC distribution system that can efficiently coordinate multiple control units, such as AC/DC converters, PVs and BESSs. In this paper, a control hierarchy is defined for undervoltage (UV) and overvoltage (OV) problems in LVDC distribution systems based on the control priority between the control units. This paper also proposes methods to determine accurate control commands for AC/DC converters and DERs. By using the proposed method, we can effectively maintain the line voltages in multi-terminal LVDC distribution systems in the normal range. The performance of the proposed voltage control method is evaluated by case studies.

• Nuclear Engineering and Technology
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• 제14권4호
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• pp.186-195
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• 1982

SYSRAN code를 사용하여 고리 1호기의 중기배관파열사고를 분석하였다. SYSRAN code는 중성자출력과 열선속계산은 각각 점근사 중성자 운동방정식과 집중정수 모형을 이용하고 냉각수 계통 과도현상에 대해서는 전 계통을 균일한 압력으로 취급하여 질량 및 에너지 평형방정식을 이용하여 계산한다. 사고 결과를 심각하게 만드는 노심상태로 부냉각재 온도계수가 커지는 노심말기와 증기발생기의 유체함량이 가장 많은 고온 정지상태를 호기조건으로 하여, 격납용기외부의 가장 큰 배관면적인 1.4f $t^2$ 크기의 증기배관이 파열되었을때 Moody critical flow model에 따라 증기가 방출된다고 가정하여 분석하였다. 그 결과 노심의 최대 열선속은 사고후 60초에 정상상대의 38%로서 FSAR의 26%에 비해 높은 값을 나타냈으나 모든 과도현상의 경향은 FSAR의 결과와 잘 일치하였다. 민감도 조사결과 이 사고는 냉각재밀도 계수와 노심 하부공간혼합인자에 가장 민감한 것으로 나타났다. B bank중 한 개의 RCCA가 완전인출 상태에서 노심에 삽입되지 않았다고 가정했을 경우의 FSAR 분석결과인 $F_{$\Delta$H}$를 3.66으로 Fz를 1.55로 하여 DNBR을 계산해 본 결과, 최소 DNBR은 1.62가 되어 핵연료의 손상은 예상되지 않았다. 점근사중성자 운동방정식, 집중 정수모형 및 질량과 에너지평형 방정식을 이용한 계통 과도 현상모델은 발전소 전 계통의 과도 현상의 경향을 연구하는데 적합한 것으로 밝혀졌다.구하는데 적합한 것으로 밝혀졌다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 하계학술대회 논문집 D
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• pp.891-893
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• 1997

In this paper an intelligent power transformer protective relaying algorithm based on Fuzzy Decision-Making is presented. The introduced protection algorithm contains several internal fuzzy rule-bases including bpa(Basic Probability Assignment: m) which are subject to off-line pre-installation by the analysis of the transformer transient characteristics for detecting the internal fault. Dempster-Shafer's rule of combination is used for the inference method with rules to decide the situation of a transformer, The proposed algorithm immunes to the saturation of transformer, inrush conditions, over excitation, and external fault. The included results of testing show practically sufficient sensitivity and selectivity of the proposed algorithm.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.2040-2041
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• 2007

In this paper, the UHF PD(Partial Discharge) sensors for $SF_6$ insulated MV $SF_6$ switchgear have been proposed and related investigations have been performed in order to detect the PD which were produced inside the MV $SF_6$ switchgear. Firstly, the internal type UHF PD sensor based on spiral antenna theory has been developed. This type sensor is highly sensitive and has lowly effect on by on-site noise. Secondly, the external type UHF PD sensor was developed based on log periodic antenna concept. This type sensor is removable and detectable for operating switchgear. These sensors were designed and simulated using RF simulation tool. In order to verify the sensitivity of these sensors, we performed the on-site test using the mock-up switchgears including the artificial defects which were the protrusion on high voltage conductor, free moving metal particle and surface defect on insulator. These mock-up switchgear were installed on the test distribution line.

• Journal of the Optical Society of Korea
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• 제7권3호
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• pp.145-149
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• 2003

The anisotropy of electron energy distribution in oxygen plasmas produced by a high intensity laser was investigated by using polarization spectroscopy. An ultra-short pulsed laser with a pulse duration of 66.5 fs and a power density of $1 {\times} 10^17/ W/$\textrm{cm}^2$$ was used. At this power density and pulse duration, the plasma was generated predominantly by optical field ionization. The degree of polarization of OVI 1s$^2$2p$^2$p2- 1s$^2$4d$^2$D$^{0}$ (J = 1/2-3/2 and 3/2-5/2) transition line at 129.92 $\AA$ was measured. O VI 1s$^2$2p$^2$P$^2$ -1s$^2$4s$^2$S$^2$ (J = 1/2-1/2 and 3/2-1/2) transition line at 132.26 $\AA$ was used to calibrate the sensitivity of the optical system. The dependencies of the degree of polarization on the initial gas density and on the laser polarization were investigated. When the laser polarization was changed from a linear to a circular polarization, the degree of polarization was decreased. When the initial gas density was increased, the degree of polarization was decreased.