• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.21 no.5
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• pp.99-105
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• 2007

This paper describes the investigation on the spot in relation to electrical safety of electrical installation in elementary middle high school. The investigation was carried out for power receiving system, classroom, chemistry room, music hall and so on. The investigation on the spot was performed by researcher, the related expert, engineer with over fifteen years of industry experience all over the country. As a result of investigation on the spot to 41 schools, common grounding methods at power receiving system were dominant. The risk factors include absence of control box of electric fan, non-installation of earth leakage circuit breaker to power source of experiment stand, use of non-grounding outlet.

• Journal of Power Electronics
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• v.18 no.5
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• pp.1536-1544
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• 2018

The existing 24-pulse autotransformer rectifier unit (ATRU) needs interphase reactors for parallel work of the rectifier bridges, and its output voltage cannot be regulated. Aiming at these problems, a step-up and step-down asymmetrical 24-pulse ATRU is proposed in this paper. The connections and turns ratios among transformer windings are well designed. In addition, a 15-degree phase difference is formed between two of the 24 voltage vectors produced by the transformer, which makes the four rectifier bridge groups produce a 24-pulse DC voltage without interphase reactors. Meanwhile, by adding extended winding to each phase of the transformer, wide-range regulation of the ATRU output voltage can be realized, and the reasonable voltage regulation range is between 0.2 and 1.6. The superposition of the voltage vectors and the principle of the voltage regulation are analyzed in detail. Furthermore, the turns ratio of the windings, winding current, output voltage, and kilovolt-ampere rating are all derived. Finally, the simulations and experiments are carried out, and the correctness of the principle and theoretical analysis of the new 24-pulse ATRU are verified.

• Journal of Power System Engineering
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• v.16 no.2
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• pp.17-23
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• 2012

The steady three-dimensional computational thermal flow analysis using standard k-${\varepsilon}$ turbulence model was carried out to investigate the heat transfer characteristics of a cabin cooler for a commercial vehicle. The heat exchanging method of this cabin cooler is to use the cooling effect of a thermoelectric module. In view of the results so far achieved, the air system resistance of a cabin cooler is about 12.4 Pa as a static pressure, and then the operating point of a cross-flow fan considering in this study is formed in the comparatively low flowrate region. The air temperature difference obtained from the cold part of an thermoelectric module is about $26^{\circ}C$, and the cooling water temperature difference obtained from the hot part of an thermoelectric module is about $3.5^{\circ}C$.

• Magazine of the Korean Society of Agricultural Engineers
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• v.38 no.5
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• pp.106-115
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• 1996

This study was carried out to provide fundamental data for reuse of resources and prevention of environmental pollution Actual states of environmental pollution by biological production facilities were investigated. Various pollution loads and quantity of wastes from greenhouse and animal housings estimated. In greenhouse contents of investigation were wastes of plastic cover, noise of heater and fan, air pollutant of heater, and wastes of soilless culture system, etc. In animal housings, those were actual state of livestock waste treatment and reuse, pollutant mass unit discharge, noise pollution, and malodorant, etc. The main pollutants discharged from greenhouses were wastes of plastic cover, rockwool, and waste fluid of nutrient solution. Developments of waste disposal methods for plastic cover and rockwool are required. And recycle technique of nutrient solution for soilless culture should be developed and propagated. With the buildup of legal control, pollutant mass discharged from livestock wastes are, on the decrease. The other side, reuse of livestock excreta increased. Most animal housings are located near the dwelling house. Malodorant and noise from animal housings have bad effects on the rural living conditions. So developments of integrated complex for small scale livestock farms are required.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.6
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• pp.753-762
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• 1998

A domestic refrigerator is composed of many components such as a compressor, evaporator, capillary tube, and the cabinet which plays a great role on the cycle performance, even if it is not the basic component part in the cycle. Recently, the restriction policy on the energy-saving and environmentally friendly refrigerator is reinforced in our nation as well as developed countries. Therefore, in this paper, cycle simulations and experiments were carried out ito understand the characteristics of the cycle performance using CFC 12, HFC 134a, and HC 600a and to know how changes in UA(overall heat transfer coefficients$\times$ heat transfer area) of evaporator, the position displacement of compressor, and the rpm of fan in the freezing room which has influence on the cycle performance. The result shows that the quantitative values of simulation and experiment are not coincident, but their trend is similar. When HFC 134a and HC 600a were used without the change of design in refrigerator used CFC 12, the performance of system in HC 600a is 30% lower, and the case of HFC 134a is 10% lower than that of CFC 12 on freezing temperature.

• Journal of the Korean Solar Energy Society
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• v.35 no.5
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• pp.49-56
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• 2015

In this study a hybrid heating system based on geothermal source and solar heat was developed in order to save energy for greenhouse heating and its field performance was evaluated. Developed system are composed of following parts: water tank, heat exchanger, heat pump, fan coil unit and heat storage unit. The working performance test was carried out in a greenhouse cultivating oriental orchids being managed by $23^{\circ}C$. Field performance test results showed that average heating coefficient of performance ($COP_h$) was 3.4 for the period from mid-January to mid-March 2013. Heating coefficient of performance ($COP_h$) of developed hybrid heat pump system was more sensitive to water tank temperature than outside air temperature. This study showed that developed hybrid heat pump system has a potential to save the heating costs up to 91% compared to conventional agricultural oil heaters.

• Korean Journal of Materials Research
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• v.9 no.4
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• pp.398-403
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• 1999

Studies on the electrical treeing deterioration and dielectric breakdown phenomena in the polymeric insulator of polyethylene and epoxy resin were carried out. Block type samples with needle-plane electrode geometry were electrically stressed and the tree pattern from the needle tip was observed. In LDPE the density of electrical tree was very high and its pattern was bush type. For the case of XLPE, branched tree was observed. As temperature and SN content increased, the dielectric breakdown voltage decreased and the treeing phenomena became more complicated. Fan type cracks were observed around the conducting tree path in the brittle DGEBA/MDA system.

• JSTS:Journal of Semiconductor Technology and Science
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• v.15 no.4
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• pp.462-470
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• 2015

In this study, we analyze the impacts of the trapezoidal fin shape of a double-gate FinFET on the electrical characteristics of circuits. The trapezoidal nature of a fin body is generated by varying the angle of the sidewall of the FinFET. A technology computer-aided-design (TCAD) simulation shows that the on-state current increases, and the capacitance becomes larger, as the bottom fin width increases. Several circuit performance metrics for both digital and analog circuits, such as the fan-out 4 (FO4) delay, ring oscillator (RO) frequency, and cut-off frequency, are evaluated with mixed-mode simulations using the 3D TCAD tool. The trapezoidal nature of the FinFET results in different effects on the driving current and gate capacitance. As a result, the propagation delay of an inverter decreases as the angle increases because of the higher on-current, and the FO4 speed and RO frequency increase as the angle increases but decrease for wider angles because of the higher impact on the capacitance rather than the driving strength. Finally, the simulation reveals that the trapezoidal angle range from $10^{\circ}$ to $20^{\circ}$ is a good tradeoff between larger on-current and higher capacitance for an optimum trapezoidal FinFET shape.

• Journal of ILASS-Korea
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• v.6 no.1
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• pp.44-51
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• 2001

The distributions of the SMD and behavior of 2% $NH_4H_2PO_4$ spray discharged from a fan-spray twin fluid type nozzle are measured and observed. The spray characteristics, according to the variation in the applied voltages, are demonstrated using the PMAS (particle Motion Analysis System) and the CCD camera, respectively. The preliminary experiments are executed to select an optimum condition for solidifying a galvanized coating layer in the uncharged condition before carrying out the main experiments. The liquid and air pressure of $0.07kgf/cm^2\;and\;0.15kgf/cm^2$ can be considered the optimum conditions to use in the main experiment. As the applied voltage increases, the frequent range of relatively large droplets diminishes. Thus, the distributions of drop diameter in the charged spray are more uniform than these in the uncharged condition. This is explained by recognizing that repulsive forces among droplets with the charges of the same sign cause them to be uniform.

• Structural Engineering and Mechanics
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• v.20 no.3
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• pp.265-277
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• 2005

This paper is focused on fractal analysis of the surface cracking, a new tool for safety evaluation of corroded reinforced concrete (RC) beams. Comprehensive experimental investigations, including flexural tests, coupon tests on strength evaluation of corroded concrete and rusty rebar, and pullout tests to determine bond strength between concrete and rebar were carried out on nine Corroded Reinforced Concrete Beams (CRCB) exposed to an aggressive environment for more than 10 years. In combination with test results from a previous study on CRCBs fabricated in the laboratory from accelerated methods, it is found that, for both types of beams, the surface cracking distributions are fractal in character at loading and failure stages. Fractal dimension is calculated for all specimens at different corrosion states based on fractal analysis method. Relationships between the fractal dimension and mechanical properties of corroded concrete, rebar corrosion ratio, and ductility of CRCBs are discussed in detail. It is concluded that the fractal dimension can act as a damage index and can be efficiently used to describe the corrosion state of CRCBs.