• Journal of Electrical Engineering and Technology
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• 제8권3호
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• pp.524-529
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• 2013

Recently, researchers have become interested in natural ester fluids, as they are an environmentally friendly alternative to mineral oils. Natural ester fluids are a natural resource made from plants; they have higher biodegradability, flash, and fire points, and a greater permittivity compared to conventional mineral oils. However, natural ester fluids also have a higher pour point, viscosity, and water content. These characteristics can hamper circulation and impair the electrical properties of an oil-filled transformer. A large amount of data has been accumulated over the years in regards to mineral insulating oil involving dielectric breakdown voltage and lightning impulse tests. However, natural ester fluids have not had their electrical properties sufficiently characterized. In this paper, we present an investigation into the characteristics of the electrical discharge development in natural ester fluids and in an oil-filled transformer near the pour points. The experiment results show that the electrical properties decreased according to a decrease in the ambient temperature and freezing time. It was found that the pour point and water content of natural ester fluids have a significant effect on the electrical properties.

• Journal of Electrical Engineering and Technology
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• 제13권4호
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• pp.1682-1691
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• 2018

Natural ester is a suitable substitute for mineral oil and has been widely used in AC transformer in many countries. In order to further application of natural ester in direct current (DC) equipment, it is needed to investigate its long term insulation property under DC condition. In this paper, a thermal ageing experiment was conducted for both mineral oil-paper and natural ester-paper insulation. The DC breakdown and space charge characteristics of insulation paper impregnated with natural ester and mineral oil was compared. Results show that the resistivity of the paper immersed in natural ester and mineral oil both increase as the ageing goes on. While insulation paper impregnated with natural ester has higher resistivity and DC breakdown voltage than the paper impregnated with mineral oil. The DC breakdown voltage for the oil impregnated insulation paper being DC pre-stressing is higher than that without pre-stressing. The average DC breakdown field strength difference between the test with pre-stressing and without pre-stressing clearly shows that there is an apparent enhancement effect for the homo-charge injection on the DC breakdown.

• Natural Product Sciences
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• 제6권2호
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• pp.53-55
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• 2000

In the course of continous work for the discovery of anti-thrombotic constituents from tubers of Gastrodia elata, citric acid 1,5-dimethyl ester was isolated from ethylacetate soluble fraction prepared from the methanol extract. The structure of the compound was determined by the spectroscopic data. The anti-thrombotic effect of this compound was observed with prolonging the bleeding time in thrombin-induced thrombosis model of mice.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2010년도 하계학술대회 논문집
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• pp.81-81
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• 2010

This paper presents results of experimental investigations on natural ester regarding the breakdown strength. Aging of insulating material in a pole transformer has been studied by performing accelerated thermal aging test. Sealed aging test vessels containing copper, laminated core, Krapt paper and insulating oil(Natural oil and Mineral oil) were aged at $140^{\circ}C$ for 30days. Compared to the conventional transformer oil, electric property of the natural ester fluid is excellent.

• 한국식품영양과학회지
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• 제46권9호
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• pp.1122-1127
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• 2017

바나나 껍질과 파인애플 껍질에서 식품의 향에 가장 많이 사용되는 ethyl butyrate를 합성할 수 있는 ester synthetase의 최적 조건을 확립하고자 반응표면분석(response surface methodology, RSM)을 사용하였다. RSM 분석 결과 바나나 껍질에서 회수한 ester synthetase의 ethyl butyrate 합성 최적 조건은 ethanol의 농도가 38.7050 mM, butyric acid의 농도가 50.9019 mM, 반응시간이 4.3662시간일 때 최대 예측값은 45.8199 mM이었다. 파인애플 껍질에서 회수한 ester synthetase의 ethyl butyrate 합성 최적 조건은 ethanol의 농도가 54.6502 mM, butyric acid의 농도가 58.7638 mM, 반응시간이 4.7436시간일 때 최대 예측 값은 65.1087 mM임을 알 수 있었다. 결론적으로 ethyl butyrate 합성을 위해서는 바나나 껍질에서 회수한 ester synthetase보다는 파인애플 껍질에서 회수한 ester synthetase가 더 효율이 높음을 알 수 있었다. 앞으로 이들의 연속 대량 생산을 위해서 효소의 고정화 방법과 연속적인 기질 투입을 위한 기술 등의 개발이 더 이루어진다면 천연향 원료의 개발이 가능할 것으로 판단된다.

• 전기학회논문지P
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• 제64권4호
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• pp.236-240
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• 2015

Natural ester has a higher biodegradability, flash and fire points, and a greater permittivity compared to conventional mineral oils. However, natural ester also has a higher pour point, viscosity, and water content. These characteristics hamper circulation and the electrical properties of oil-filled transformer. Thus, this paper applied electromagnetic-thermal-flow coupled analysis method to predict temperature distribution inside 154kV single phase power transformer using natural ester. It modeled in the actual appearance for the tank and winding of the power transformer to improve the accuracy of analysis and applied heat flow analysis that considered hydromechanics and heat transfer at the same time. It calculated the power loss, the main cause of temperature rise, from winding and core with electromagnetic analysis then used for the heat source for the heat flow analysis. It then compared the reasonability of result of measurement analysis based on the result acquired from temperature rise test using FBG sensor on the power transformer.

• Archives of Pharmacal Research
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• 제19권1호
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• pp.66-70
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• 1996

Aliphatic esters of protocatechuic acid (PA, 1), vanillic acid (VA, 9) and gallic acid (GA, 18) were prepared and their anti-thrombotic effects were evaluated in the mouse model of thrombosis. The aliphatic groups included methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, n-amyl and cyclohexyl. n-Amyl ester of PA (7), i-propyl and cyclohexyl esters of VA (13 and 17 respectively) and ethyl ester of GA (20) treatment significantly lowered the death rate and increased the recovery from paralysis due to the thrombotic challenge. From the limited analogs available, it was tentatively concluded that the structural conformation, where carboxy oxygen (=O or -O) of the carboxyl group (COOH) at $C_1$ and the oxygen function at $C_3(either\; OH\; or\; OCH_3)$ are closely situated, is favorable for the esters of PA, VA and GA to be more antithrombotic.

• Composites Research
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• 제27권1호
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• pp.19-24
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• 2014

본 연구에서 아마/비닐에스테르(Flax/vinyl ester)를 적용한 친환경 구조물 설계를 위한 선행 연구로서 아마/비닐 에스테르 자연 섬유 복합재료의 기계적 물성치를 분석하였다. 시편 제작을 위해 VARTM 제작 공법이 적용되었다. 참고문헌에서 제시한 자연 섬유 복합재료의 물성치와 본 연구에서 제작된 시편의 물성치를 비교하였다. 이 결과를 바탕으로 아마/비닐 에스테르 복합재료가 친환경 구조물에 적용하는 것이 유리함을 확인하였다.

• Archives of Pharmacal Research
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• 제8권4호
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• pp.229-236
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• 1985

Oxidation of presenegenin dimethyl ester triacetate with chromium trioxide in acetic acid yielded two compounds, 11-ketone (IV) and 12-ketone (IV) derivatives. The latter was a main product. On mild alkaline hydrolysis, IV afforded 11-keto-presenegenin dimethyl ester (V), mp 232-$234^{\circ}$, $C_{32}H_{48}O_{8}$, whereas VI did 12-keto-presenegenin dimethyl ester 12, 27-hemiketal (VIII), mp 240-$242^{\circ}$, $C_{32}H_{50}O_{8}$.

• 전기학회논문지
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• 제60권6호
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• pp.1163-1168
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• 2011

Most transformers use insulating and cooling fluids derived from petroleum crude oil, but mineral oil has some possibility of environmental pollution and fire with explosion. vegetable oil fluids extracted from seed has superior biodegradation and fire-resistant properties including an exceptionally high fire point enhancing fire safety. In this study, it is aimed at the practicality of substituting natural ester dielectric fluid for mineral oil in liquid insulation system of transformers. As a rise in coil winding temperature has a direct influence on transformer life time, it is important to evaluate the temperature rise of coil winding in vegetable oil in comparison with mineral oil. Four transformers for the test are designed with 10KVA, 13.2KV, one phase unit. The temperature are directly measured in insulating oil of these transformers with the two sorts of natural ester and mineral oil dielectric fluid respectively. Experiment for aging carry out two means. First means remained $120^{\circ}C$ that transformer of mineral oil were operated at 185% load. Second means is that insulating oils of two natural ester and mineral oil were aged by thermal cycles repeating from $30^{\circ}C$ to $120^{\circ}C$. For the heating, Transformers were operated at 185% load. For the cooling, cooling system was operated in the chamber. Samples were analyzed at 42, 63, 93, 143, 190, 240 300cycles. Analysis contents are dielectric strength, total acid value. Mineral oils compared results of first means with results of second means. And compared two sort natural esters respectively with mineral oil in second means.