• 조명전기설비학회논문지
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• 제29권11호
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• pp.41-46
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• 2015

This study was conducted to discover a substitute of $SF_6$ gas. $SF_6$ gas is widely used across the industries. Thanks to superior electrical properties, in particular, it has been commonly used in electrical industry. However, there have been a lot of studies on its serious effect on global warming. As a substitute of this synthetic gas, a mixture of dry air and $N_2/O_2$ was chosen in this study. In case of $N_2/O_2$, dielectric strength differs depending on the mixing ratio. This study examined dielectric breakdown and flashover after adjusting oxygen percentage in the dry air. This test was conducted in a quasi-uniform electric field depending on pressure, oxygen concentration and gas mixtures. The test results found that dielectric voltage and flashover voltage were the highest at a certain oxygen concentration. It is the results of this photoionization and electron attachment of oxygen.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1994년도 하계학술대회 논문집 C
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• pp.1574-1576
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• 1994

$SF_6$ gas has become an important insulation medium in modern electric power apparatus, because of its high insulation withstand levels and good arc quenching capability. For the application of $SF_6$ gas in GIS the estimation of insulation properties is a fundamental point. Moreover the reduction of withstand levels in case of inhomogeneous fields caused by particles or fixed protrusions is of special interest. It is known that the presence of free conducting particles in GIS can significantly lower the insulating level of $SF_6$ gas at elevated pressure and also it has been recently shown that dielectric strength is greatly reduced by fast transients such as disconnector surges where metallic particles are involved. In this paper, we have disigned the particle test chamber rated 362kV for the purpose of investigating the discharge characteristics in SF6 gas where inhomogenius fields are caused by metallic particles.

• Journal of Electrical Engineering and Technology
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• 제13권3호
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• pp.1337-1345
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• 2018

The reliability of power transmission and distribution depends up on the consistency of insulation in the high voltage power transformer. In recent times, considering the drawbacks of conventional mineral oils such as poor biodegradability and poor fire safety level, several research works are being carried out on natural ester based nanofluids. Earlier research works show that sunflower oil has similar dielectric characteristics compared with mineral oil. BIOTEMP oil which is now commercially available in the market for transformers is based on sunflower oil. Addition of nanofillers in the base oil improves the dielectric characteristics of liquid insulation. Only few results are available in the literature about the insulation characteristics of nano modified natural esters. Hence understanding the influence of addition of nanofillers in the dielectric properties of sunflower oil and collecting the database is important. Considering these facts, present work contributes to investigate the important characteristics such as partial discharge, lightning impulse, breakdown strength, tandelta, volume resistivity, viscosity and thermal characteristics of $SiO_2$ nano modified sunflower oil with different wt% concentration of nano filler material varied from 0.01wt% to 0.1wt%. From the obtained results, nano modified sunflower oil shows better performance than virgin sunflower oil and hence it may be a suitable candidate for power transformer applications.

• Transactions on Electrical and Electronic Materials
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• 제13권3호
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• pp.116-120
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• 2012

In this paper, ZnO-Epoxy nanocomposites (NEP) were prepared and epoxy composites that contain 5 wt% micro ZnO (MEP) and deliberately not well dispersed nano ZnO (NDNEP) were also prepared for purpose of comparison. The effects of the particle size and dispersion of ZnO on dielectric properties of epoxy resin were chiefly studied. Test results showed that: at a loading of 5 wt%, the three epoxy composites seem to have no significant difference on resistivity compared to epoxy resin; Dielectric constants of all the epoxy composites are also basically the same but they are bigger compared to that of the pure epoxy resin (unfilled); Dielectric dissipation factors ($tan{\delta}$) of NDNEP is greater than that of NEP and MEP. NEP has the minimum dielectric loss factor, whereas dielectric loss factors of the three epoxy composites are larger than that of the pure epoxy resin. The decreasing order of electrical breakdown strength for the three epoxy composites and for the pure epoxy resin is as follows: NEP>MEP>NDNEP>EP. Finally, in order to explain the experimental results the aggregation interface phase was proposed. Furthermore, addition of well dispersed nano filler has proved to have a positive effect on the improvement of the dielectric properties of epoxy resin.

• 한국전기전자재료학회논문지
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• 제28권8호
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• pp.508-512
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• 2015

Some insulating materials are tested and analyzed with variables to obtain the reliable pressboard which is located to core and coil of high voltage transformer. The high voltage transformer is used in electrical power system and operating reliability. Optimization possibility of pressboard shape including electrical insulation performance could be achieved by analysis simulation. Using insulating pressboard, which is made by mold applied eddy current loss, it could be measured the influences of moisture content for electrical properties. As a result, it is to contribute to improve the performance and ensure the reliability of the pressboard by investigating electrical strength according to the variation oil temperature. In addition pressboard thickness is important design factor to ensure electrical strength in high voltage transformer.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 추계학술대회 논문집 전력기술부문
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• pp.391-394
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• 2001

Occurring forest fire or burning bushes beneath overhead transmission lines have caused system disturbances in many countries. In this study, various tests in the simulated condition of power lines were conducted so as to investigate the reduction in insulation strength caused by combustion flame. The results of an experimental investigation into the flashover characteristics of air dielectric strength in the presence of oil flame are reported. It is demonstrated that flame can reduce by more than half, 80% in maximum, the breakdown voltage of a model line.

• 한국초전도ㆍ저온공학회논문지
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• 제17권3호
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• pp.33-36
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• 2015

A liquid nitrogen ($LN_2$) is usually used to be a coolant and insulant for a HTS coil system. HTS wires for a superconducting apparatus may be surrounded by gaseous nitrogen ($GN_2$) due to film boiling generated by a quench or voids occurred by electrical breakdown. The increased maximum electric field intensity at $GN_2$ may result in the degradation of dielectric strength of a HTS coil system. In this paper, a study on the dielectric characteristics of a composite insulation system composed of $LN_2$ and $GN_2$ is performed. A sphere-to-plane electrode system made with stainless steel is used to perform the experiments under AC and lightning impulse voltage condition. A sphere electrode is surrounded by $GN_2$ and a plane electrode is immersed into $LN_2$ to conduct dielectric experiments with a composite insulation system. The dielectric experiments are performed according to the level of $LN_2$ from the plane electrode to a sphere electrode. It is found that the dielectric characteristics of a composite insulation system are dependent on the level of $LN_2$ and the field utilization factor of an electrode system.

• 마이크로전자및패키징학회지
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• 제24권4호
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• pp.39-46
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• 2017

본 연구는 평판형 히터용 금속방열판상의 세라믹 절연층 제조, 즉 절연성 금속기판에 관한 것이다. 반도체나 디스플레이의 열처리 공정 등에 사용되는 평판형 히터를 제조함에 있어서, 온도 균일도를 높이기 위해 금속 방열판으로서 열전도율이 높고, 비교적 가벼우며, 가공성 좋은 알루미늄 합금 기판이 선호된다. 이 알루미늄 기판에 발열 회로 패턴을 형성하기 위해서는 금속 기판에 절연층으로서 고온 안정성이 우수한 세라믹 유전체막을 코팅하여야 한다. 금속 기판상에 세라믹 절연층을 형성함에 있어서 가장 빈번히 발생하는 첫 번째 문제는 금속과 세라믹의 이종재료 간의 큰 열팽창계수 차이와 약한 결합력에 의한 층간박리 및 균열발생이다. 두 번째 문제는 절연층의 소재 및 구조적 결함에 따른 절연파괴이다. 본 연구에서는 이러한 문제점 해소를 위해 금속소재 기판과 세라믹 절연층 사이에 완충층을 도입하여 이들 간의 기계적 매칭과 접합력 개선을 도모하였고, 다중코팅 방법을 적용하여 절연막의 품질과 내전압 특성을 개선하고자 하였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 춘계학술대회 논문집 유기절연재료 방전 플라즈마연구회
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• pp.61-64
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• 2003

In the response to an increasing demand for electrical energy, much effort aimed to develop and commercialise HTS power equipments is going on around the world. For the development, it is necessary to establish the dielectric technology in $LN_2$. Hence many types of dielectric tests should be carried out to understand the dielectric phenomena at cryogenic temperature and to gather various dielectric data. Among the many types dielectric tests, the barrier effect were conducted with the simulated electrode after analysing the insulating configuration of the pancake coil type HTS transformer. The influence of a barrier on the dielectric strength was measured according to the size and the position of the barrier. It was shown that the effectiveness, the ratio of the breakdown voltage in presence of barrier to the voltage without barrier, is highest when the barrier is placed at the needle electrode side. And the barrier effect was not depend on the electrode array. The life time to breakdown with decreasing the applied voltage was increased remarkably having wide error band but the shape parameter in Weibull distribution was almost constant.

• 전기학회논문지
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• 제56권9호
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• pp.1561-1565
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• 2007

According to thermal degradation on power transformers, it is known that electrical, mechanical and chemical characteristics for power transformer's oil-paper are changed. In the chemical property, especially, when the kraft paper is aged, the cellulose polymer chains break down into shorter lengths. It causes decrease in both tensile strength and degree of polymerization of paper insulation. Also the paper breakdown is accompanied by an increase in the content of various furanic compounds within the dielectric liquid. It is known that furanic components in transformer oil come only from the decomposition of insulating paper rather than from the oil itself. Therefore the analysis of furanic degradation products provides a complementary technique to dissolved gas analysis for monitoring transformers when we evaluate the aging of insulating paper by the total concentration of carbon monoxide and carbon dioxide dissolved in oil only. Recently, the analysis of furanic compounds by high performance liquid chromatography(HPLC) using IEC 61198 method for estimating degradation of paper insulation in power transformers has been used more conveniently for assessment of oil-paper. It is know that the main products which is produced by aging are 2-furfuryl alcohol, 2-furaldehyde(furfural), 2-furoic acid, 2-acetylfuran, 5-methyl-2-furaldehyde, and 5-hydroxymethyl-2-furaldehyde. For investigating the accelerated aging process of oil-paper samples we manufactured accelerating aging equipment and we estimated variation of insulations at $140^{\circ}C$ temp. during 500 hours. Typical transformer proportions of copper, silicon steel and iron have been added to oil-paper insulation during the aging process. The oil-paper insulation samples have been measured at intervals of 100 hours. Finally we have analyzed that 2-furoic acid and 2-acetylfuran products of furanic compounds were detected by HPLC, and their concentrations were increased with accelerated aging time.