• 한국전기전자재료학회논문지
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• 제20권7호
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• pp.631-635
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• 2007

Diagnostic, surge and ac breakdown tests are widely used to evaluate the insulation condition of stator winding in traction motor. Diagnostic test included ac current, tan delta and maximum partial discharge. The result of diagnostic test indicates that five kinds of stator windings are good condition. Surge test was peformed to confirm the healthy of turn insulation in stator windings. This test is very easy to detect the turn insulation failure between normal and defect stator windings. After completing the diagnostic test, ac breakdown test has conducted gradually increasing ac voltage, until the stator winding punctured. No. 5 stator windings failed near rated voltage of 18.9 kV The breakdown voltage of No. 1 stator windings was 13.0 kV The ac breakdown voltage of normal winding is about 1.45 times higher than that of defect windings. The failure was located in a line-end coil at the exit from the core slot.

• 한국전기전자재료학회논문지
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• 제28권6호
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• pp.390-395
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• 2015

Molded insulation materials are widely used from large electric power transformer apparatus to small electrical machinery and apparatus. In this study, by adding MgO with the average particle of several tens nm and the excellent thermal conductivity into molding material, we improved the problem of insulation breakdown strength decrease according to rising temperature in overload or in bad environmental condition. We confirmed the life evaluation by using the insulation breakdown and inverse involution to investigate the electrical characteristics of nano-composites materials. By using a scanning electron microscope, it is confirmed that MgO power with the average particle size of several tens nm is distributed and the filler particles is uniformly distributed in the cross section of specimens. And it is confirmed that the insulation breakdown strength of Virgin specimens is rapidly decreased at the high temperature area. But it is confirmed that the insulation breakdown strength of specimens added MgO slow decreased by thermal properties in the high temperature area improved by the contribution of the heat radiation of MgO and the suppression of tree. The results of life prediction using inverse involution, it is confirmed that the life of nano-composites is improved by contribution of MgO according to the predicted insulation breakdown strength after 10 years of specimens added 5.0 wt% of MgO is increased about 2.9 times at RT, and 4.9 times at $100^{\circ}C$ than Virgin specimen, respectively.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 춘계학술대회 논문집 유기절연재료 전자세라믹 방전플라즈마 연구회
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• pp.76-78
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• 2001

In this paper insulation cover that being used in distribution line have been evaluated for aging characteristics. For evaluating its aging properties, we dismounted a variety of samples, like insulation covers for termination of deadend clamp, bushing, LA, COS and sleeve, in the fields. we performed mechanical properties test, electrical test, weathering test, etc. of these samples. And these samples are compared with virgin sample. Test results shows the bad mechanical strength in some part of samples. Especially, Insulation covers for the bushing terminations have cracks in the surface of samples.

• Structural Engineering and Mechanics
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• 제77권5호
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• pp.673-689
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• 2021

This paper addresses the efficiency of thermal insulation layers applied to protect structural elements strengthened by fiber-reinforced polymers (FRP) in the case of fire event. The paper presents numerical modeling and nonlinear analysis of reinforced concrete (RC) columns externally strengthened by FRP and protected by thermal insulation layers when subjected to elevated temperature specified by standard fire tests, in order to predict their residual capacity and fire endurance. The adopted numerical approach uses commercial software includes heat transfer, variation of thermal and mechanical properties of concrete, steel reinforcement, FRP and insulation material with elevated temperature. The numerical results show good agreement with published results of full-scale fire tests. A parametric study was conducted to investigate the influence of several variables on the structural response and residual capacity of insulated FRP-confined columns loaded by service loads when exposed to fire. The residual capacity of FRP-confined RC column was affected by concrete grade and insulation material and was shown to improve substantially by increasing the concrete cover and insulation layer thickness. By increasing the VG insulation layer thickness 15, 32, 44, 57 mm, the loss in column capacity after 5 hours of fire was 30%, 13%, 7% and 5%, respectively. The obtained results demonstrate the validity of the presented approach for estimation of fire endurance and residual strength, as an alternative for fire testing, and for design of fire protection layers for FRP-confined RC columns.

• 한국수소및신에너지학회논문집
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• 제29권4호
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• pp.386-392
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• 2018

Fuel cells are known as eco - friendly energy facilities that can use heat energy and electric energy at the same time. Fuel cells are classified according to the temperature and material used, and solid oxide fuel cell (SOFC) is relatively high temperature ($700-800^{\circ}C$). SOFC requires a hot box consisting of a high temperature stack, a reformer, a burner, and the heat exchangers in order to use energy efficiently. The hot box needs to maintain heat insulation performance at high temperature to reduce heat loss. However, Fibrous insulation, which is widely used, needs to be improved because it has a disadvantage that the thermal conductivity is rapidly increased due to the increase of temperature. Therefore, this study was carried out to develop a thermal insulation, which is applied to multiple layers insulation (MLI) technic, that can be used under SOFC operating conditions and prevent a drastic drop in thermal conductivity at high temperature. The developed insulation is consist of a thermally conductive material, a spacer, and a reflective plate. The thermal conductivity of the insulation was measured by in the thermal conductivity measuring device at high temperature range. As a result, it was confirmed that the developed layers insulation have an good thermal conductivity (0.116 W/mK) than fibrous insulation (0.24 W/mK) as a radiation shielding effect at a high temperature of 1,173 K.

• 한국전기전자재료학회논문지
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• 제26권10호
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• pp.726-730
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• 2013

In order to develop a high voltage insulation material, spherical silicas with two average particle sizes of 5 ${\mu}m$ and 20 ${\mu}m$ were mixed in different mixing ratios (1:0, 0.7:0.3, 0.5:0.5, 0.3:0.7, 0:1) and their total filling content was fixed at 65 wt%. In order to observe the dispersion of the spherical silicas and the interfacial morphology between silica and epoxy matrix, field emission scanning electron microscope (FE-SEM) was used. The electrical insulation breakdown strength was estimated in sphere-plate electrodes with different insulation thicknesses of 1, 2, and 3 mm. Electrical insulation breakdown strength decreased with increasing mixing ratio of 5/20 ${\mu}m$ and the thickness dependence of the breakdown strength was also observed. The tensile strength of the neat epoxy was 82.8 MPa as average value and its increased with decreasing particles size and that of epoxy/silica (2 ${\mu}m$) was 107 MPa, which was 130.8% higher value.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 추계학술대회 논문집 Vol.19
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• pp.336-338
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• 2006

Diagnostic tests are used to evaluate the insulation condition of stator windings in traction motor. These tests included ac current, tan delta and maximum partial discharge. The insulation condition of stator windings was assessed by three test items. The stator windings of traction motor were m good condition. After completing the diagnostic tests, the stator windings of traction motors were subjected to gradually increasing ac voltage, until the insulation punctured. No.5 stator windings failed near rated voltage of 18.9 kV. The breakdown voltage of No.1 stator windings was 13.0. The failure was located m a line-end coil at the exit from the core slot.

• 전기의세계
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• 제14권2호
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• pp.8-13
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• 1965

It is expected that the impurities contained in a solid state insulation material will affect a considerable influence on its break-down voltage, dielectric loss, and insulation resistance. In this thesis, as a preliminary experimental research for the investigation described above, the effect of metalic barrier between the electrodes on the creepin flash over discharge voltage along the surface of a solid insulation material has been investigated, and got some interesting results. It was found that generaly the flash over voltage rises when a metalic barrier is located between the electrodes. The results of this investigation will be taken into account as an important components on the insulation design to prevent the creeping flash over discharge in insulators, bushings, and so on.

• 한국전기전자재료학회논문지
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• 제20권2호
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• pp.135-141
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• 2007

The conduction-cooled HTS SMES is operated in cryogenic and high vacuum condition. Thus, Insulation design at cryogenic temperature and high vacuum is a key and an important element that should be established to accomplish miniaturization that is a big advantage of HTS SMES. However, the behaviors of insulators for cryogenic conditions in vacuum are virtually unknown. Therefore, we need active research and development of insulation concerning application of the conduction-cooled HTS SMES. Therefore, in this study, we experimented about insulation characteristic high vacuum and cryogenic similar to driving condition of SMES system. Also, investigated about insulation characteristic of suitable some materials to insulator for conduction-cooled HTS SMES. As this results, we possessed basis data for insulation materials selection and insulation design for development of 600 kJ class conduction-cooled HTS SMES.

• 설비공학논문집
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• 제25권3호
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• pp.119-125
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• 2013

IInsulation material is generally used for preventing heat loss from heat transport fluids, and water absorption severely reduces the insulation property. The purpose of this study is to evaluate the amount of water absorption supplied by the pouring method and spraying method, to investigate the effects of water absorption on the thermal conductivity of an insulation material, and modeling the relation between water absorption and thermal conductivity. E-glass, a kind of glass fiber, and HYPERLITE, mainly composed of pearlite, are selected, to compare hygroscopic and insulation properties. E-glass is found to have much higher water absorptivity, compared to HYPERLITE. The thermal conductivity of the water-absorbed E-glass is increased by more than 150%, compared to that of no absorption, while variation of the thermal conductivity of HYPERLITE with water absorption is insignificant. A three-stage model of water absorption for thermal conductivity is developed, and the modeling results are found to be in good agreement with the experimental data.