• Journal of Power Electronics
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• 제15권3호
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• pp.685-694
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• 2015

The power loss of the controllable switches in modular multilevel converter (MMC) HVDC transmission systems is an important factor, which can determine the design of the operating junction temperatures. Due to the dc current component, the approximate calculation tool provided by the manufacturer of the switches cannot be used for the losses of the switches in the MMC. Based on the enabled probabilities of each SM in an arm, the current analytical models of the switches can be determined. The average and RMS currents can be obtained from the corresponding current analytical model. Then, the conduction losses can be calculated, and the switching losses of the switches can be estimated according to the upper limit of the switching frequency. Finally, the thermal resistance model of the switches can be utilized, and the junction temperatures can be estimated. A comparison between the calculation and PSCAD simulation results shows that the proposed method is effective for estimating the junction temperatures of the switches in the MMC.

• Journal of Electrical Engineering and Technology
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• 제12권2호
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• pp.858-864
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• 2017

This study aims to restrain free conducting wire-type particles which are commonly and dangerously existing within DC gas-insulated transmission lines. A realistic platform of a coaxial cylindrical electrode was established by using a high-speed camera and a partial discharge (PD) monitor to observe the motion, PD, and breakdown of these particles. The probabilities of standing or bouncing, which can be affected by the length of the particles, were also quantitatively examined. The corona images of the particles were recorded, and particle-triggered PD signals were monitored and extracted. Breakdown images were also obtained. The air-gap breakdown with the particles was subjected to mechanism analysis on the basis of stream theory. Results reveal that the lifting voltage of the wire particles is almost irrelevant to their length but is proportional to the square root of their radius. Short particles correspond to high bouncing probability. The intensity and frequency of PD and the micro-discharge gap increase as the length of the particles increases. The breakdown voltage decreases as the length of the particles decreases.

• 한국전기전자재료학회논문지
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• 제19권10호
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• pp.907-911
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• 2006

In this paper, we propose a new structure that improves the on-state voltage drop and switching speed in Insulated Gate Bipolar Transistors(IGBTs), which can be widely used in high voltage semiconductors. The proposed structure is unique in that the collector area is divided by $SiO_2$, whereas the conventional IGBT has a planar P+ collector structure. The process and device simulation results show remarkably improved on-state and switching characteristics. Also, the current and electric field distribution indicate that the segmented collector structure has increased electric field near the $SiO_2$ corner, which leads to an increase of electron current. This results in a decrease of on-state resistance and voltage drop to $30%{\sim}40%$. Also, since the area of the P+ region is decreased compared to existing structures, the hole injection decreases and leads to an increase of switching speed to 30 %. In spite of some complexity in process procedures, this structure can be manufactured with remarkably improved characteristics.

• Journal of Electrical Engineering and Technology
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• 제11권2호
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• pp.436-444
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• 2016

Oil-paper insulation of valve-side windings in converter transformers withstand electrical stresses combining with AC, DC and strong harmonic components. This paper presents the physical mechanisms and experimental researches on partial discharge (PD) of oil-paper insulation at pulsating DC voltage. Theoretical analysis showed that the phase-resolved distributions of PDs generated from different insulated models varied as the increase of the applied voltages following a certain rule. Four artificial insulation defect models were designed to generate PD signals at pulsating DC voltages. Theoretical statements and experimental results show that the PD pulses first appear at the maximum value of the applied pulsating DC voltage, and the resolved PD phase distribution became wider as the applied voltage increased. The PD phase-resolved distributions generated from the different discharge models are also different in the phase-resolved distributions and development progress. It implies that the theoretical analysis is suitable for interpretation of PD at pulsating DC voltage.

• 한국전기전자재료학회논문지
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• 제30권4호
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• pp.214-217
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• 2017

An IGBT (insulated gate bipolar transistor) device has an excellent current-conducting capability. It has been widely employed as a switching device to use in power supplies, converters, solar inverters, and household appliances or the like, designed to handle high power. The aim with IGBT is to meet the requirements for use in ideal power semiconductor devices with a high breakdown voltage, an on-state voltage drop, a high switching speed, and high reliability for power-device applications. In general, the concentration of the drift region decreases when the breakdown voltage increases, but the on-resistance and other characteristics should be reduced to improve the breakdown voltage and on-state voltage drop characteristics by optimizing the design and structure changes. In this paper, using the T-CAD, we designed the NPT-IGBT (non punch-through IGBT) and FS-IGBT (field stop IGBT) and analyzed the electrical characteristics of those devices. Our analysis of the electrical characteristics showed that the FS-IGBT was superior to the NPT-IGBT in terms of the on-state voltage drop.

• 에너지공학
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• 제26권3호
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• pp.105-112
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• 2017

우리는 원자력발전시스템에서부터 상수도까지 많은 배관시스템을 사용하고 있다. 그리고 이들 배관시스템의 적절한 운용을 위하여 배관시스템의 유지 및 보수 등을 수행하고 있다. 특히 한국지역난방공사와 같은 대형플랜트 배관시스템의 고장은 기업의 생산성과 이익에 직결된 문제일 뿐만 아니라 국민의 안전과 편익과 같은 매우 중요한 문제를 유발할 수 있기 때문에 빠른 대응과 안전한 수리가 가장 중요한 문제로 대두되고 있다. 본 연구에서는 한국지역난방공사 사용 중인 이중보온 열수송관(300A)의 유지보수를 위하여 액화질소를 이용한 배관 동결차수공법을 개발하였다. 본 연구에서는 전산해석기법을 채용하여 대상 열수송관과 전용 재킷에 대한 내부 유동 및 열전달 해석을 수행하여 최적의 시스템을 선정하고, 상세 모델을 설계, 제작하였다. 실험실 규모 시험장치를 개발하여 차수공법에 대한 자체시험을 수행하고, 한국지역난방공사 세종지사 Test bed에서 현장적용 성능평가 시험을 수행하였다.

• Journal of Electrical Engineering and Technology
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• 제10권1호
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• pp.344-354
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• 2015

In order to study the development of partial discharge (PD) under typical protrusion defects in gas-insulated switchgear, we applied step voltages on the defect and obtained the ${\varphi}-u$ and ${\varphi}-n$ spectrograms of ultra-high frequency (UHF) PD signals in various PD stages. Furthermore, we extracted seven kinds of features to characterize the degree of deterioration of insulation and analyzed their values, variation trends, and change rates. These characteristics were inconsistent with the development of PD. Hence, the differences of these features could describe the severity of PD. In addition, these characteristics could provide integrated characteristics regarding PD development and improve the reliability of PD severity assessment because these characteristics were extracted from different angles. To explain the variation laws of these seven kinds of parameters, we analyzed the relevant physical mechanism by considering the microphysical process of PD formation and development as well as the distortion effect generated by the space charges on the initial field. The relevant physical mechanism effectively allocated PD severity among these features for assessment, and the effectiveness and reliability of using these features to assess PD severity were proved by testing a large number of PD samples.

• Journal of Electrical Engineering and Technology
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• 제9권6호
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• pp.2036-2041
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• 2014

In this paper, a thermal model is developed for the bus bar system to predict the temperature variation during the transient time period and to calculate both the steady-state and transient electrical current carrying capacity (ampacity) of bus bar. The bus bar system installed in the power house of Kumaraguru College of Technology, Coimbatore has been considered. Temperature variation predicted in the modelling is validated by observing the current and steady state temperatures in different feeders of the bus bar. Magnetic field of the extreme phases R and B induces more current in the middle phase Y. Hence, the steady state temperature in the phase Y is greater than other two phases. The transient capabilities of the bus bar are illustrated by calculating the variations in the bus bar temperature when it is subjected to a step change in current during the peak hours due to increase in hostel utilities and facilities (5.30 pm to 10.30 pm). The physical and geometrical properties of the bus bar and temperature variation in the bus bar are used to estimate the thermal time constants for common bus bar cross-sections. An analytical expression for the time constant of the bus bar is derived.

• 한국안전학회지
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• 제23권4호
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• pp.47-52
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• 2008

Many researches on fire risk for normal electric wiring have been pursued in advanced countries such as the USA and Japan, but comparative studies of the partial disconnection and normal state of electric wires have not been conducted. Detection system for the cause of partial disconnection is not developed and prevention countermeasure for electrical fire by the cause is not effective. Therefore, in this paper, partial disconnection characteristics on electric wires were derived and analyzed by experiment and electrical-thermal finite element method(Flux 3D) on the model wires which consist of VCTF(PVC insulated PVC sheathed Cap Tyre Flexible Cord, KS C 3304) and IV(lndoorwire PVC, KS C 3302). VCTF is used in wiring portable electric appliances and the IV is used indoors. Interrelationships between partial disconnection premonitory symptom and current were derived and analyzed by the characteristics based on experiments and thermal analysis for electric wire according to current under normal state and 200% overload state of rated current.

• 전기전자학회논문지
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• 제22권2호
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• pp.339-343
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• 2018

본 연구는 IGBT 구조에서 JFET 영역의 드라이브 인 확산거리 및 JFET영역의 윈도우의 크기에 따라서 항복전압과 온상태 전압강하 특성을 분석하였다. 시간은 동일하게 하면서 온도를 상승시켜 확산거리를 조정하였으며, 그 결과 항복전압은 감소되나, 온 상태 전압 강하 특성은 현저하게 좋아지는 것을 알 수 있었다. 따라서 드리프트 층의 비저항을 변화시켜 항복전압을 1440V로 고정하여 1.15V의 낮은 온 상태 전압 강하 값을 얻을 수 있었다. 따라서 본 연구결과를 토대로 Planar Gate IGBT에서는 JFET 영역의 공정 및 설계 파라미터를 효율적으로 조절한다면 같은 항복전압을 기준으로 상당히 낮은 온 상태 전압 강하 값을 확보할 수 있어, 소비전력의 측면에서 충분히 활용할 수 있을 것으로 판단된다.