• Journal of the Korea Institute of Building Construction
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• v.21 no.1
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• pp.21-29
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• 2021

The objective of this study is to evaluate the effect of the application of double layered bubble sheet on the curing of slab and wall concrete placed at the job site in cold weather and to offer a feasibility of Concrete IoT Management System(CIMS), which is wireless sensor network developed by the authors, to manage early age quality of the concrete in terms of temperature, maturity and strength development. Test results indicated that the application of bubble sheet enhances the insulation performance, which results in an increase of the temperature by around 1~20. 6℃. It is found that CIMS can gather the temperature, maturity and strength development data from the sensors embedded from 30 m far from CIMS successfully. Predicted compressive strengths by CIMS had good agreement with measured ones within 2 MPa error level until 7 days. It is thought that the combination of the bubble sheet application for cold weather protection and CIMS for quality management tool in cold weather concreting contributes to shorten the time for the form removal by one day.

• Progress in Superconductivity and Cryogenics
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• v.24 no.4
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• pp.40-45
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• 2022

The electrical/thermal stabilities and magnetic field controllability of a no-insulation (NI) high-temperature superconducting magnet are characterized by contact resistance between turn-to-turn layers, and the contact resistance characteristics are determined by properties of conductor surface and winding tension. In order to accurately predict the electromagnetic characteristics of the NI coil in a design stage, it is necessary to control the contact resistance characteristics within the design target parameters. In this paper, the contact resistance and critical current characteristics of a rare-earth barium copper oxide (REBCO) conductor were measured to analyze the effects of surface treatment conditions (roughness and oxidation level) of the copper stabilizer layer in REBCO conductor. The test samples with different surface roughness and oxidation levels were fabricated and conductor surface analysis was performed using scanning electron microscope, alpha step surface profiler and energy dispersive X-ray spectroscopy. Moreover, the contact resistance and critical current characteristics of the samples were measured using the four-terminal method in a liquid nitrogen impregnated cooling environment. Compared with as-received REBCO conductor sample, the contact resistance values of the REBCO conductors, which were post-treated by the scratch and oxidation of the surface of the copper stabilizer layer, tended to increase, and the critical current values were decreased under certain roughness and oxidation conditions.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.5
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• pp.310-314
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• 2000

To study the basic research of the lightning parameters for power system operation, LPATS(Lightning Positioning and Tracking System) has been introduced since 1995 in KEPCO(Korea Electric Power Corporation). We have developed the lightning parameters analysis program which can produce accumulative magnitude distribution of lightning current and IKL map by LPATS data. We obtained the various statistical distributions of lightning current parameters since 1996 by the lightning analysis program for the pertinent insulation design. In this paper, we describe the LPATS system in KEPCO, the statistical distribution of lightning current parameters and the IKL(Isokeraunic Level) map from 1996 to 1998. And the compared results between the calculated LFOR(lightning flashover rate) and the observed rate are also described.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.46 no.1
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• pp.70-81
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• 2010

A mathematical model is formulated to study the effect of wall mass on the thermal performance of four different houses of different construction. This analytical study was motivated by the experimental work of Burch et al. An analytical solution of one -dimensional, linear, partial differential equation for wall temperature profiles and room air temperatures is obtained using the Laplace transform method. Typical Meteorological Year data are processed to yield hourly average monthly values. These discrete data are then converted to a continuous, time dependent form using a Fast Fourier Transform method. This study is conducted using weather data from four different locations in the United States: Albuquerque, New mexico; Miami, Florida; Santa Maria, California; and Washington D.C. for both winter and summer conditions. A computer code is developed to calculate the wall temperature profile, room air temperature, and energy consumption loads. Three sets of results are calculated one for no auxiliary energy and two for different control mechanism -- an on-off controller and a proportional controller. Comparisons are made for the cases of two controllers. Heavy weight houses with insulation in mild weather areas (such as August in Santa Maria, California) show a high comfort level. Houses using proportional control experience a higher comfort level in comparison to houses using on-off control. The result shows that there is an effect of mass on the thermal performance of a heavily constructed house in mild weather conditions.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2005.05a
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• pp.47-50
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• 2005

In this paper, we investigate a filtering technique to reduce the adverse effect of long motor leads on H-bridge cascaded 7-level inverter fed ac motor drive. The switching surge voltage becomes the major cause to occur the insulation failure by serious voltage stress in the stator winding of high voltage induction motor. However, the effect of switching surge appears un seriousin high voltage induction motor than low voltage induction motor. Consequently, we demonstrated that the filter connected to the motor terminals greatly reduces the transient voltage stress and ringing, moreover we show lowers the dv/dt of the inverter switching pulse. The results of simulation show the suppression of dv/dt and the reduced peak voltage at the motor end of a long cable.

• Environmental Analysis Health and Toxicology
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• v.22 no.1 s.56
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• pp.37-47
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• 2007

Aldehydes are irritants of the upper respiratory tract with symptoms such as eye, nose, and throat. Formaldehyde classified in Group 2A by the International Agency for Research on Cancer and a probable human carcinogen by the Unite States Environmental Protection Agency due to its carcinogenicity. Aldehydes may be emitted from many other consumer products, such as permanent press fabrics, cosmetics, fiberglass insulation, paints, and coatings. The purpose of this study was to examine the does-response relationship between aldehydes levels and symptoms (eyes, nose, throat, and respiratory) for 36 dwellings and 280 households in Korea. As a result, environmental factors affecting aldehydes level were indoor smoking, ventilation, using of carpet, bed, and new furniture, painting for renovation, and indoor humidity. There wat weakly positive correlation between symptom score and aldehydes level.

• Proceedings of the KIEE Conference
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• 2002.07c
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• pp.1903-1905
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• 2002

The degree of contamination on outdoor insulator is one of the most important factors for the determination of insulation level. And the salt, NaCl, is known as the most dangerous contaminants in the most region of the world. As shown through the preceding study, we could find the close relationship between the generation and deposition of salt contaminants and the meteorological conditions. To analyze the relationship, we monthly measured the ESDD for some sites with brush wiping method, and daily measured the density for one site with the automatic measuring apparatus. And, with the measured data and the meteorological data from KMA(Korea Meteorological Administration), we analyzed the relationship between the two factors with regression method. Through the results of this investigation, we could quantify the comparative contribution of the climatic factors for the pollution level of outdoor insulator, and the results could be used as a useful reference for the maintenance of overhead lines and substations.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.29 no.1
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• pp.1-6
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• 2017

In order to better save energy, many buildings have been constructed with high levels of insulation and airtightness in recent years. Additionally, having high quality indoor air has become more relevant, necessitating a ventilating system. This study is aimed at evaluating the performance of a humidity exchanger through computational fluid dynamics (CFD) analysis of elements for the purpose of providing comfortable indoor air and reduced energy consumption. The simulation was conducted with three different shapes (triangle, rectangular, and curve) of heat exchanger elements, in order to find the most effective element. A follow-up simulation then proved the efficiency of the chosen humidity exchanger, which was selected by analyzing the results of the preceding simulation, comparing study data with measurement data from the Korea Testing Laboratory (KTL). The resulting analysis revealed that the rectangular element showed the lowest level of efficiency in both heating and cooling, while the curved element showed the highest level of efficiency in both heating and cooling.

• Journal of the Semiconductor & Display Technology
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• v.19 no.1
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• pp.42-48
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• 2020

As global warming accelerates, eco-friendly electric cars are being developed to reduce carbon dioxide emissions, and power conversion inverters are used to drive motors. Among inverter components, DC-link capacitor is heated by high current usage, which causes problems such as performance and life-saving of inverter. Although metal cases with good thermal performance have been used to solve this problem, it is difficult to apply them in practice due to insulation problems with other parts. In this paper, the Heat-Generation influence factor of DC-link capacitor is analyzed. Variables on heat-generation are set at 3 levels for film width, inductance, and film thickness. Box-Behnken to 13 tests using the design and minimal deviations, e.g. through the experiment three times by each level. The surface of the film k type by attaching the sensor current is measured temperature. Capacitance was set to a minimum level of 200 ㎌ and had a frequency of 16 kHz with Worst case, ambient temperature of 85℃ and a ripple current of 50 Ams was applied. The temperature at the measurement point was collected in the data logger after sampling at 1 minute intervals for 2 hours after saturation with the ambient temperature. This experiment confirmed that setup factors are correlated with heat-generation.

• Computers and Concrete
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• v.21 no.6
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• pp.637-647
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• 2018

Numerical approach using finite element method has been used to evaluate the behaviour of reinforced concrete frame structure subjected to fire. The structure is previously designed in accordance with Eurocode standards for the design of structures for earthquake resistance, for the ductility class M. Thermal and structural response are obtained using a commercially available software ANSYS. Temperature-dependent nonlinear thermal and mechanical properties are adopted according to Eurocode standards, with the application of constitutive model for the triaxial behaviour of concrete with a smeared crack approach. Discrete modelling of concrete and reinforcement has enabled monitoring of the behaviour at a global, as well as at a local level, providing information on the level of damage occurring during fire. Critical regions in frame structures are identified and assessed, based on temperatures, displacements, variations of internal forces magnitudes and achieved plastic deformations of main reinforcement bars. Parametric analyses are conducted for different fire scenarios and different types of concrete aggregate to determine their effect on global deformations of frame structures. According to analyses results, the three-dimensional finite element model can be used to evaluate the insulation and mechanical resistance criteria of reinforced concrete frame structures subjected to nominal fire curves.