• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.150-150
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• 2009

In this paper, various kinds of epoxy based nanocomposites were made and AC breakdown properties of nano-$TiO_2$ and micro-silica filler mixture of epoxy based composites were studied by sphere to sphere electrode. Moreover, nano- and micro-filler combinations were adopted as an approach toward practical application of nanocomposite insulating materials. AC breakdown test was performed at room temperature $(25^{\circ}C)$, $80^{\circ}C$ and $100^{\circ}C$. The result shows breakdown strength about non-filled, nano-scale $TiO_2$, micro-scale silica and nano-$TiO_2$, micro-silica filled epoxy composites.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.2136-2137
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• 2011

본 연구에서는 몰드변압기의 다양한 진단방법 연구를 위해 몰드변압기의 진동을 측정 분석하였다. 현장에서 사용되어지고 있는 3상 몰드변압기를 용량별로 진동수를 측정하고 FFT 분석을 실시하였다. 현장실측을 통해 몰드변압기의 상태진단을 진동으로 확인할 수 있었다. 진동주파수만을 측정하여 판단하는 것은 어려움이 있었으며, 단, 삼상변압기의 각 상에 대한 비교평가는 가능한 것으로 확인되었다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.6
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• pp.538-543
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• 2008

Nanostructured materials are attracting increased interest and application. Exciting perspectives may be offered by electrical insulation. Epoxy/Organoclay nanocomposites may find new and upgraded applications in the electrical industry, replacing conventional insulation to provide improved performances in electric power apparatus, e.g, high voltage motor/generator stator winding insulation, dry mold transformer, etc. In the paper work, the electrical and thermal properties of epoxy/organoclay nanocomposites materials were studied. The electrical insulation characteristics were analyzed through the permittivity characteristics. by analyzing the permittivity spectra, it was found that dielectric constant becomes smaller with increase frequency and becomes larger with increase temperature. This indicates restriction of molecular motion and strong bonds at the epoxy/organoclay nanocomposites. The morphology of nanocomposites obtained was examined using TEM and X-ray diffraction. It has been shown that the presence of polar groups leads to an increased gallery distance and partial exfoliation. Nevertheless, full exfoliation of clay platelets has not been achieved.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.840_841
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• 2009

본 논문은 2차원 유한요소법을 이용하여 2[MVA]급 몰드변압기의 과도전계를 해석한 것이다. 과도현상을 해석하기 위해 변압기 코일 및 대지 간 정전용량을 에너지법을 이용하여 구하였고, 이를 이용하여 변압기에 충격전압 95[kV]가 인가될 경우에 변압기 위치별 전계의 세기를 구하였다.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.784_785
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• 2009

본 논문에서는 2[MVA]급 배전용 몰드변압기의 온도분포를 유한요소해석을 통하여 수행하였다. 몰드변압기의 온도상승한도와 허용최고온도를 전자기적 열원에 대한 분석을 통하여 계산하고 그 계산된 열원을 바탕으로 열적 해석의 열원으로 사용하여 계산하였다. 일반적으로 변압기의 수명은 내부의 전반적인 열적 특성보다는 특정 부위의 온도 분포에 의해 결정되며, 특히 변압기 내부 최고점의 온도(hot spot temperature)값이 허용치 이상으로 상승할 경우 절연내력의 저하로 인해 변압기의 수명은 급격히 감소한다. 이러한 수명개선을 위해 몰드 변압기의 철심과 고압.저압권선의 Joule's loss을 계산하여 열원을 계산하였고, 그 결과를 토대로 배전용 몰드변압기의 철심과 고압 저압권선의 온도상승 분포와 최고점의 온도분포를 예측하였다.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.5
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• pp.649-656
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• 2013

A conventional epoxy-microsilica composite (EMC) and an epoxy-microsilica-nanosilicate composite (EMNC) were prepared in order to apply them to mold-type transformers, current transformers (CT) and potential transformers (PT). Nanosilicate was exfoliated in a epoxy resin using our electric field dispersion process and AC insulation breakdown strength at $30{\sim}150^{\circ}C$, glass transition temperature and viscoelasticity were studied. AC insulation breakdown strength of EMNC was higher than that of EMC and that value of EMNC was far higher at high temperature. Glass transition temperature and viscoelasticity property of EMNC was higher than those of EMC at high temperature. These results was due to the even dispersion of nanosilicates among the nanosilicas, which could be observed using transmission electron microscopy (TEM). That is, the nanosilicates interrupt the electron transfer and restrict the mobility of the epoxy chains.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.101-101
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• 2010

Power distribution system requires the transformer with higher capacity than ever, but this ever, but this may be the cause of the increasing of short circuit current in contrast to conventional one when short-circuit accident is occurred. Therefore molded case circuit breaker improved in aspects of interrupting capacity of short circuit current in this system is needed. The arrangement and quality of the material of grids in arc quenching room are also designed optimally by the analysis of arc driving forces.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.681-682
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• 2008

최근 다양한 부하들로 인해, 배전용변압기로 사용되고 있는 몰드변압기의 운전조건이 가혹해 지고 있다. 특히, 전력변환장치와 연계된 몰드변압기의 경우, 부하의 운전특성에 따라 편자(偏磁)현상이 발생하며 이로 인해 직류성분의 전류가 몰드변압기로 유입된다. 이는 철심의 포화현상 및 변압기의 손실 증가를 유발하여 국부과열 문제로 인한 사고로 이어질 우려가 있다. 본 연구에서는 이러한 문제를 해결하기 위해, EMTP 과도해석 프로그램을 활용하여 직류성분 전류에 의해 증가되는 몰드변압기의 여자전류를 계산하고, 이를 토대로 철심의 자속밀도 변화를 계산하였다. 직류성분 전류의 크기에 따라 철심의 적정 운전자속밀도를 고려하여 몰드변압기를 설계함으로써 직류전류 유입시에도 안정적인 운전이 가능할 것으로 사료된다.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 1997.10a
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• pp.70-73
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• 1997

This paper describes the technique for detecting failure symptom of mold transformer. This study uses the vibration signal analysis method and FEM as the technique. A loading back method is constructed for experiment, accelation sensors are adhered for measurement of vibration signal. Vibration signal measured by this method is analyzed into variation trend of measurement variables by control of control variables. Magnetic field distribution of molded winding is also acquired by FEM considering the design specfication and the characteristics of insulation material, in conclusion, he relation of results between vibration signal and FEM is studied by these methods.

• Proceedings of the KIEE Conference
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• 2005.11c
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• pp.107-109
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• 2005

Temperature distribution measured to estimate condition of an electrical apparatus is an absolute reference for the apparatus conditions and the difference between the reference temperature and the current one. Because a passive thermography without the external thermal stimulation shows the difference in surface temperature between the object and back ground, the results can apply only to the estimation or the monitoring for the condition of terminal loose and the overload pertaining to the rise in temperature. However, a thermal flow in the active thermography is differently generated by the structure and condition of the surface and subsurface. This paper presents the nondestructive testing using the behavior and deals with the results by heat injection and cooling to the apparatus. The buried discontinuity of subsurface could be detected by these techniques.