• Journal of the Korean Wood Science and Technology
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• 제18권2호
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• pp.36-48
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• 1990

This experiment was carried out to improve the quality of high absorbent polymer which has excellent absorptivity and water retention compared to pulp and absorption sheet, through absorption characteristics-absorptive power, water retention, absorption rate, gel strength, pH, particle size, and moisture content. - of six polymers, namely, anionic polyacrylamide, cationic polyacrylamide, polyacrylic, acid polyvinyle alcohol 500, and 1500, and a-cellulose. and to examine the possibility of substitution of amide groups for carboxyl group and/or hydroxyl group which were commercial high absorbent polymer by comparing the absorption characteristics of the polymers. Polyacrylamide has high absorptive power and water retention, but has low gel strength and poor absorption rate. The rest of polymers were similiar to ${\alpha}$-cellulose in every respect. Thus, polyacrylamides could be replaced with polyacrylic acid and polyvinyl alcohol which are presently a high absorbent polymers. In comparing the absorption characteristics and the absorptive power of the polymers-anionic polyacrylamide, cationic polyacrylamide, polyacrylic acid, polyvinyle alcohol. a-cellulose-the absorptive power was in inverse proportion to the gel strength and absorption rates, affected by the particle size and pH change.

• 한국위성정보통신학회논문지
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• 제11권1호
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• pp.1-5
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• 2016

본 논문에서는 L-Band 대역의 항행안전시설(DME, TACAN)에 적용 가능한 광대역 High power pulsed amplifier를 구현하였다. L-Band 대역의 항행안전시설의 특성상 구현된 SSPA는 매우 높은 출력과 선형성, 효율 특성을 요구한다. 이에 본 논문에서는 변형된 class F 기법을 이용하여 효율 특성을 개선하였다. 또한 hybrid coupler를 이용한 Balance 구조와 구동부 증폭단의 비선형 특성을 이용한 anti-phase 기법, 출력부 harmonic trap 등을 이용하여 선형 특성을 개선하였다. 구현된 SSPA는 약 300MHz의 대역폭을 가지며, 1.5KW 출력과 55%의 효율 특성을 보였다.

• 조명전기설비학회논문지
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• 제26권12호
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• pp.1-8
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• 2012

The performance and lighting characteristics of the LED depend on cooling condition because the power LED generates lots of heat. In this paper, the effect of the generated heat from power LED module on lighting characteristics and performance is measured and evaluated. For experiments, the transient temperature of a power LED module with cooling condition is measured. In addition, the temperature and lighting characteristics of the LED module are measured during the steady state. As a result, the cooling condition is less effective on the lighting characteristics of the LED module at rated current but the cooling condition extremely affects those of the LED module over the rated current. Because high temperature of the power LED module causes the low phosphor conversion, luminance efficiency becomes low and color temperature becomes high. When power LED module are driven over the rated condition, higher temperature is directly related to lighting characteristics and performance of the LED module rather than higher current.

• KIEE International Transactions on Electrophysics and Applications
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• 제4C권5호
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• pp.207-214
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• 2004

This paper presents the characteristics of transient and effective impulse impedances for deeply driven grounding electrodes used in soil with high resistivity or in downtown areas. The laboratory test associated with the time domain performance of grounding piles subjected to a lightning stroke current has been carried out using an actual-sized model grounding system. The ground impedances of the deeply driven ground rods and grounding pile under impulse currents showed inductive characteristics, and the effective impulse ground impedance owing to the inductive component is higher than the power frequency ground impedance. Both power frequency ground impedance and effective impulse ground impedance decrease upon increasing the length of the model grounding electrodes. Furthermore, the effective impulse ground impedances of the deeply driven grounding electrodes are significantly amplified in impulse currents with a rapid rise time. The reduction of the power frequency ground impedance is decisive to improve the impulse impedance characteristics of grounding systems.

• Journal of Electrical Engineering and Technology
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• 제10권1호
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• pp.216-226
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• 2015

The neutral beam injection generate ultra-high temperature energy in the tokamak of nuclear fusion. The neutral beam injection make up arc power supply, filament power supply and acceleration & deceleration power supply. The arc power supply has characteristics of low voltage and high current. Arc power supply generate arc through constant output of voltage and current. So this paper proposed suitable buck converter for low voltage and high current. The proposed buck converter used parallel switch because it can be increased capacity and decrease conduction loss. When an arc generated, the neutral beam injection chamber occur high voltage. And it will break output capacitor of buck converter. Therefore the output capacitor was removed in the proposed converter. Thus the proposed converter should be designed for the characteristics of low voltage and high current. Also, the arc power supply should be guaranteed for system stability. The proposed parallel buck converter enables the system stability of the divided low output voltage and high current. The proposed converter with constant output be the most important design of the output inductor. In this paper, designed arc power supply verified operation of system and stability through simulation and prototype. After it is applied to the 288[kW] arc power supply for neutral beam injection.

• 한국지진공학회논문집
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• 제24권3호
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• pp.123-128
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• 2020

Analysis of the 2016 Gyeongju earthquake and the 2017 Pohang earthquake showed the characteristics of a typical high-frequency earthquake with many high-frequency components, short time strong motion duration, and large peak ground acceleration relative to the magnitude of the earthquake. Domestic nuclear power plants were designed and evaluated based on NRC's Regulatory Guide 1.60 design response spectrum, which had a great deal of energy in the low-frequency range. Therefore, nuclear power plants should carry out seismic verification and seismic performance evaluation of systems, structures, and components by reflecting the domestic characteristics of earthquakes. In this study, high-frequency amplification factors that can be used for seismic verification and seismic performance evaluation of nuclear power plant systems, structures, and equipment were analyzed. In order to analyze the high-frequency amplification factor, five sets of seismic time history were generated, which were matched with the uniform hazard response spectrum to reflect the characteristics of domestic earthquake motion. The nuclear power plant was subjected to seismic analysis for the construction of the Korean standard nuclear power plant, OPR1000, which is a reactor building, an auxiliary building assembly, a component cooling water heat exchanger building, and an essential service water building. Based on the results of the seismic analysis, a high-frequency amplification factor was derived upon the calculation of the floor response spectrum of the important locations of nuclear power plants. The high-frequency amplification factor can be effectively used for the seismic verification and seismic performance evaluation of electric equipment which are sensitive to high-frequency earthquakes.

• KEPCO Journal on Electric Power and Energy
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• 제5권3호
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• pp.229-233
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• 2019

Large-scale High Temperature Superconducting (HTS) wind power generators suffer from high electromagnetic force and high torque due to their high current density and low rotational speed. Therefore, the torque and Lorentz force of HTS wind power generators should be carefully investigated. In this paper, we proposed a Performance Evaluation System (PES) to physically test the structural stability of HTS coils with high torque before fabricating the generator. The PES is composed of the part of a pole-pair of the HTS generator for estimating the characteristic of the HTS coil. The 10 MW HTS generator and PES were analyzed using a 3D finite element method software. The performance of the HTS coil was evaluated by comparing the magnetic field distributions, the output power, and torque values of the 10 MW HTS generator and the PES. The magnetic flux densities, output power, and torque values of the HTS coils in the PES were the same as a pole-pair of the 10 MW HTS generator. Therefore, the PES-based evaluation method proposed in this paper can be used to estimate the critical characteristics of the HTS generator under high magnetic field and high torque before manufacturing the HTS wind turbines. These results will be used effectively to research and manufacture large-scale HTS wind turbine generators.

• 전력전자학회논문지
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• 제24권5호
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• pp.319-326
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• 2019

The use of high-voltage gain converters is essential for distributed power generation systems with renewable energy sources, such as fuel and solar cells, due to their low-voltage characteristics. In this study, a novel high-voltage gain non-isolated buck boost converter topology is proposed to cope with the need of a high-voltage conversion ratio without the transformer for the renewable energy sources. Given that the proposed topology utilizes the cascode structure, the voltage gain and the efficiency are higher than those of other conventional non-isolated converters. To demonstrate the feasibility of the proposed topology, the operation principle is presented, and the steady-state characteristics are analyzed in detail. The validity of the proposed converter is verified by experiments with a 400 W prototype converter.

• 전기학회논문지
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• 제60권9호
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• pp.1727-1732
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• 2011

In order to realize a high performance(low loss, high isolation) microwave power divider/combiner, we have designed the power combiner/divider precisely in accordance with the different hight of central part. In the case of the high central part of the hight of $h_r$=10.2, a compensating part of the conical line is inserted in the conical conversion transmission line, and in the case of low central part of the hight of $h_r$=5.0, the conical conversion transmission line is remodeled into the 2-stage bend structure. In both case, the reflection characteristics are improved to 30dB over the operating frequency range of 5GHz bandwidth. A resistance is inserted between the peripheral ports so as to try to improve the isolation characteristics of the device. For the 16-divider/combiner, the isolation characteristics are improved to 10dB over the operating frequency range of 5GHz bandwidth.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2017년도 전력전자학술대회
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• pp.577-595
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• 2017

${\bullet}$ Silicon Carbide (SiC) had excellent material properties as the base material for next generation of power semiconductor. In developing SiC MOSFET, gate oxide reliability issues had to be first overcome before commercial application. Besides, a high and stable gate-source voltage threshold $V_{GS(th)}$ is also an important parameter for operation robustness. SiC MOSFET with such characteristics can directly use existing high-speed IGBT gate driver IC's. ${\bullet}$ The linear voltage drop characteristics of SiC MOSFET will bring lower conduction loss averaged over full AC cycle compared to similarly rate IGBT. Lower switching loss enable higher switching frequency. Using package with auxiliary source terminal for gate driving will further reduce switching losses. Dynamic characteristics can fully controlled by simple gate resistors. ${\bullet}$ The low switching losses characteristics of SiC MOSFET can substantially reduce power losses in high switching frequency operation. Significant power loss reduction is also possible even at low switching frequency and low switching speed. in T-type 3-level topology, SiC MOSFET solution enable three times higher switching freqeuncy at same efficiency.