• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.6
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• pp.143-148
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• 1994

In order to study the effect of D.C resistivity of sample on electromagnetic loss of ferrite at microwave frequency, samples were prepared for having differences in resistivity of an order of two. Microwave permeability($\mu$), permitivity($\varepsilon$) and effective linewidth(${\Delta}H_{eff}$), and ferromagnetic resonance linewidth(${\Delta}$H) were characterized. Tan${\delta}{\mu}$, tan${\delta}{\varepsilon}$ and ${\Delta}H_{eff}$ were decreased with increasing the resistivity and (${\Delta}$H) was increased with increasing Fe concentration, which was due to an increase of anisotropy magnetic field (=Ha).

• Journal of the Korea Safety Management & Science
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• v.7 no.4
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• pp.101-110
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• 2005

The likelihood of failure for the thinning of high temperature sulfide and naphthenic acid corrosion, which affect to a risk of facilities, was analyzed through the risk based inspection using API-581 BRD. We found that the corrosion rate was increased with increasing temperature and total acid number(TAN). And maximum value of the technical module subfactor(TMSF) was not varied with operating condition, but the TMSF was sensitively changed at the range of low temperature, low flow rate, and high TAN. Also, the TMSF was increased as an used year and inspection effectiveness increased, but it was increased as thickness, inspection number, and over design decreased.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.279-280
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• 2008

Accelerated aging tests were conducted under laboratory conditions on two generator stator bars. Electrical stress is applied in No. 1 model stator bar. Electrical and thermal stresses are applied in No. 2 model stator bar. As aging times increased from 0 to 4780h, diagnostic tests were performed on No. 1 and No. 2 model stator bars. Diagnostic tests included AC current, dissipation factor(tan$\delta$) and partial discharge magnitude. The ${\Delta}tan{\delta}$ and $\Deta$I of No. 1 and No. 2 model stator bars increased with increased in aging time.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.447-449
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• 1999

In this paper, we were evaluated dielectric properties and temperature dependency in aging semifilm and PET film. According to humidity, dielectric properties of PET film increased, but tan $\delta$ presented a constant transition. According as temperature increased, tan $\delta$ increased from 1.9$\times$10$^{-3}$ to 2.76$\times$10$^{-3}$ and capacitance increased from 244.1(PF) to 297.5(PF).

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.10
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• pp.847-858
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• 2000

The aging characteristics of 2 kinds of 3 years field-aged distribution polymer insulators which were dismounted from 5 regions have been investigated by electrical test and material characterization. Although the tan $\delta$of specimens prepared from weathershed was increased with surface aging, the tan $\delta$and leakage current of real products had no difference between virgin and dismounted ones. Due to the aging, all dismounted polymer insulators had micro-cracks on the surface of weathershed and only the products of manufacturer B showed the reduction of OIT(oxidation induction time). But, there were no differences between virgin and dismounted products in contact angle and chemical structure. Therefore, it can be considered that the aging is only limited on the surface of dismounted polymer insulators and that NMR technique are very useful to evaluate the aging of polymer materials.

• Journal of the Korean Society of Safety
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• v.4 no.1
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• pp.5-14
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• 1989

Deterioration induced by partial discharge was investigated for low-density polyethylene samples. Under an electrical field, a cold-drawn PE film was stretched perpendicularly to the direction of the original drawing. The starting voltage of the discharge shows a minimum at the draw ratio of 1.2 to 1.8. Around the same draw ratio, the elastic modulus and mechanical loss factor (tan S) of the sample exhibit a minimum and a maximum, respectively. According to the X-ray analysis, the size itf microcrystals decreases with increasing draw ratios. Reorientation of the ru01ecular chains was observed above a draw ratio of 1.5 by the IR method.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.40 no.12
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• pp.1242-1251
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• 1991

This paper is to investigate the tree growth phenomena and the characteristics of $\varepsilon$' and tan$\delta$ for the effect of ultrasonic wave on polymer insulation material. The conclusions are as follows. 1) As the pressure amplitude of ultrasonic wave is larger and its irradiated time is longer, tree inception voltage and its breakdown voltage in specimen are smaller, and tree growing is faster. 2) As the irradiated quantity of ultrasonic wave is more increased, the value of tan$\delta$ is larger, but the value of $\varepsilon$' is almost constant. 3) The effect by the pressure amplitude of ultrasonic wave is greater than that by its irradiated time on the insulation characteristics of polymer material.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.61-64
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• 2000

Three kinds of treeing inhibitors are added to investigate the effect on electrical properties of XLPE. The treeing inhibitors are barbituric acid, 4- (4-Nitrophenylazo) resorcinol and 4-(4-Nitrophenylazo) naphthol. Added amount of each treeing inhibitors varied form 0phr to 2.0phr. In order to know the changes of electrical properties, break down strength, tan$\delta$, and $\varepsilon$$_{r}$ were measured. Experimental results showed that electrical properties of each sample was slightly changed by amount of additives.s.

• Proceedings of the KIEE Conference
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• 2003.07c
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• pp.1722-1725
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• 2003

절연물에 가해지는 열화 중에서 열 사이클(Thermal cycle) 열화를 모사하기 위하여, 대형 터빈 발전기 수냉각 고정자 권선용 바를 대상으로 IEEE Std 1310 규격에 따라 200 사이클의 열 사이클 열화 시험을 수행하였다. 바에 대한 절연 특성을 분석하기 위하여 시험 수행 전후의 Tan ${\delta}$ 및 Tip-up(%, ${\Delta}$ Tan ${\delta}$), 부분방전의 최대 방전량 등을 측정하였고 또한 바를 절단하여 절연물 내의 박리와 도체와 절연물 간의 분리 등을 점검하였다. 최종적으로는 절연파괴 시험을 수행하여 절연파괴 강도를 측정하였다. 시험 결과 초기 절연 특성상의 현저한 변화는 없었으며 양호한 특성을 보였다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.11
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• pp.938-942
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• 2000

Radiation effects on dielectric properties of low density polyethylene(LDPE) were investigated using the various measurements of FT-IR, gel content and elongation at break. FT-IR spectra showed that polar groups were comprised in LDPE due to radiation treatment. It was also confirmed that the formation of polar groups on LDPE caused the increased dielectric properties such as permittivity and tan $\delta$. However, in this study, any evidence of decreasing permittivity was not found although the morphological change of LDPE could be identified from the increasing gel content and the decreasing elongation.