• The Transactions of the Korean Institute of Electrical Engineers
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• v.40 no.6
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• pp.574-581
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• 1991

Damage in film capacitors has been investigated, using FTIR and ESCA, aiming to elucidate the nature of electrode removal and the possibility of base films to be damaged. Also, tests were conducted to investigate the effect of a long-term thermal aging at elevated temperatures. Unsuccessful clearing or grape-clustering processes can induce a long-term degradation which involves the chemical and morphological changes. Major changes are the oxidation and the decrease in surface crystallinity possibly arising from the corona discharge. An immediate deterioration of BOPP film may occur when the air entrapped between the film layers induces an extensive autocatalytic oxidative degradation. This type of immediate damage may result in a premature failure at an early stage of qualification test. As far as the nature of electrode removal is concerned, a permanent removal of electrode materials was observed in the main erosion area.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.05a
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• pp.155-158
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• 2002

Fabrication process of metal/intermetallic laminated composites by using self-propagating high temperature synthesis(SHS) reactions between Ni and Al elemental metal foils have been investigated. Al foils were sandwiched between Ni foils and heated in a vacuum hot press to the melting point of aluminium. SHS reaction kinetics was thermodynamically analyzed through the final volume fraction of the unreacted Al related with the initial thickness ratio of Ni:Al and diffusion bonding stage before SHS reaction. Thermal aging of laminated composites resulted in the formation of functionally gradient series of intermetallic phases. Microstructure showed that the main phases of intermetallics were NiAl and $Ni_3Al$ having higher strength at room and high temperatures. The volume fractions of intermetallic phases were measured as 82.4, 58.6, 38.4% in 1:1, 2:1, 4:1 initial thickness ratio of Ni:Al.

• Journal of the Korean Ceramic Society
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• v.34 no.9
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• pp.986-992
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• 1997

Cordierite ceramic was prepared by sol-gel method. It was analyzed by Infrared spectroscopy and X-ray diffraction patterns that the ceramic was chemically mixed in molecular level and transformed to $\alpha$-cordierite at 125$0^{\circ}C$. Water vapour treatments for aging and drying process were conducted to get porous cordierite with thermally stable pore structure. It resulted in 220-410 $m^2$/g BET surface area and mesoporous structure with mean pore diameter, 40$\AA$. Compared to naturally dried ceramic, the ceramic showed superior thermal stability of surface area up to $700^{\circ}C$. Surfaces of porous cordierite ceramics were observed by SEM.

• Journal of Power System Engineering
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• v.20 no.4
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• pp.38-43
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• 2016

Safety-related equipments of Nuclear Power Plants(NPP) have to perform environmental qualification test in accordance with IEEE-323 standards. However, non-metallic materials replace new one regularly instead of the test because they are considered as consumable parts. In this study, the seven kinds of non-metallic materials are selected and their activation energy was experimentally evaluated with uncertainty analysis by using thermogravimetric analyzer(TGA). In order to obtain activation energy of non-metallic materials, mass difference, temperature raising rate and conversion rate on the specimen are analyzed. It is postulated that the three experiment conditions are important to get a reliable activation energy. This postulate was experimentally confirmed using Arrhenius equation and Flynn-Wall-Ozawa analysis.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.43-43
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• 2003

Carbon nanotubes(CNTs) have many application points, which are field emission devices, composites, hydrogen storage, nanodevices, supercapacitor and secondary battery. The most promising application point is emitter tip mays of field emission devices. Furthermore, it may be also useful as a vacuum device for high frequency and high power. But, there are some obstacles to fabricate carbon nanotube field emission device. One is that CNTs grown by CVD method has weak adhesion with substrate and the other is non-uniform length of them. These problems are very crucial in aging property and reliability of device in the field emission.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.2132-2133
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• 2011

본 논문에서는 차량용 수소 연료전지 냉각수의 절연열화특성을 평가하기 위해 냉각수 시료에 대해 운전온도 보다 가혹한 열 열화 조건을 인가하여 그 특성을 평가하였다. 연료전지 냉각수의 절연열화기구는 냉각수 내 이온성 불순물 증가로 인한 도전율 상승, 유기물 성분의 열열화로 인한 절연저항 및 유전특성 변화 등으로, 이는 연료전지 차량의 절연저항 저하 등의 문제를 야기시킬 수 있다. 본 논문에서는 이온성 불순물에 의한 국부적인 절연특성을 평가 하기 위해 상용 전기전도도미터를 이용한 비전도도 측정 및 열열화로 인한 유기물 성분인 절연성 부동액의 유전특성 변화를 진단하여 열 열화된 냉각수의 전기전도도 및 전기용량 특성을 평가하였다. 또한 각 시료에 대한 내전압 시험을 진행하여 열 열화와 절연파괴 특성의 관계를 확인하였다.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2005.05a
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• pp.209-213
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• 2005

To enhance the reliability of distribution transformers in service and to reduce the cost of maintaining and replaceing these, the condition and life of those insulating system should be evaluated accurately and the time to replace should be determined economically. Since the transformer failures related to insulation failure indicates that the primary cause is normally mechanical failure of integrity due to loss of mechanical strength as a result of degradation, the tensile strength characteristics of paper during ageing under accelerated conditions in insulating oil and research trends for assessing the life of insulating paper were investigated.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.481-484
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• 2001

High voltage induction motors are widely used in industrial factory because have many benefits. But the insulated materials of induction motor are aged by using time, electrical, thermal, circumstantial stresses and so on. Motor failures are occurred by these deterioration phenomena and give rise economic problems to user. In many motor failures, insulated material problems of stator winding happen frequently and occupy high percentages in the failure source. In this paper, the testing specimen(motorette) is manufactured by modeling of stator winding of high voltage induction motor and accelerating test is carried out. Partial discharge signals detected by RF sensor are used to analyze deterioration condition of stator windings. According to aging time, the 3D ( ${\Phi}$-Q-N) distribution and skewness of partial discharge signals are changed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.04a
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• pp.326-329
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• 1997

The surface of mica/epoxy paper(130${\mu}{\textrm}{m}$) is investigated with SEM(scanning electron microscope). SEM micrographs revealed that thermal aging has a strong influence on aged specimens. The mica/epoxy paper was exposed at 187$^{\circ}C$ in an ordinary electrical oven for 72hour. Stater windings from two generators were measured by tan delta(tan $\delta$)and maximum partial discharge(Qm). The values of tan $\delta$and Qm were fecund to be higher for new generator than old one. The insulation condition of mica/epoxy paper were measured by ac current and tan $\delta$. Test results are observed that the sound specimens are higher than those aged. Model bar coils subjected to various accelerated agings were evaluated by Qm.

• Korean Journal of Materials Research
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• v.7 no.8
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• pp.650-653
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• 1997

In large generators in power plants, stator winding insulations is exposed to a combination of thermal, electrical, mechanical, environmental stresses in service. These combined stresses cause insulation aging which leads to final insulation breakdown. In order to identify the breakdown mechanism, the stator winding insulation materials which are composed of mica-epoxy is analyzed by the component of materials with EDS, SEM techniques. We concluded that the potassium ions of mica are replaced by hydrogen ions at boundary area of mica-epoxy and/or mica-mica. It is proposed that through these phenomena, the conductive layers of potassium ions enable high voltage fields of multiple stresses to create voids and microcracks.