• 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.

• Journal of Electrical Engineering and Technology
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• 제11권1호
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• pp.184-191
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• 2016

In recent years, there are a number of studies that have been carried out to explore the alternative for Mineral Oil (MO) as dielectric insulating fluid in transformers due to the increasing tight regulation on safety and environment. Vegetable oils have been identified as suitable candidate since it is biodegradable, non-toxic and high flash/fire points which ensure more in-service safety. Among the types of vegetable oils considered for transformers application are Palm Oil (PO) and Coconut Oil (CO). This paper presents an experimental study on the lightning breakdown voltages of PO and CO under non-uniform electric field based on needle-sphere electrodes configuration at 3 small gap distances. The type of PO used in this study is Refined Bleached and Deodorized Palm Oil (RBDPO) Olein. The main focus of this study is to examine the lightning breakdown performance of RBDPO and CO under different test conditions and assess its suitability as dielectric insulating fluid in transformers. The effect of voltage polarities (positive and negative) and testing methods (rising-voltage, up-and-down and multiple-voltage) were investigated. The data obtained from all tests were analysed by Weibull distribution in order to determine the withstand voltages for each type of oils. It was found that the breakdown voltages of RBDPO and CO are comparable with MO under positive lightning impulse. Under negative lightning impulse, the breakdown voltage of MO is slightly higher than RBDPO and CO. There is no significant effect of testing methods and voltage polarities on lightning breakdown voltages of RBDPO and CO. Based on the statistical analysis, it is found that the breakdown voltages of RBDPO and CO at 1% probability are slightly lower than MO.

• Journal of Electrical Engineering and Technology
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• 제12권6호
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• pp.2333-2341
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• 2017

Mineral oils are commonly used as transformer insulation oils but these oils are obtained from non-renewable and non-sustainable sources, which is highly undesirable. For this reason, natural ester oils are now being used in replacement of mineral oils because of their good biodegradability, high cooling stability, good oxidation stability and excellent insulation performance. Nanotechnology has gained prominence in both academic and industrial fields over the years and it has been shown in previous studies that nanoscale materials are useful for transformers due to their favourable dielectric properties. The objective of this study is to compare the AC breakdown voltage and viscosity of natural ester oil with three types of nanofluids. The natural ester oil-based nanofluids are prepared by mixing palm fatty acid ester (PFAE) oil with three types of nanoparticles at a concentration of 0.01 g/l: (1) $Fe_3O_4$ conductive nanoparticles, (2) $TiO_2$ semi-conductive nanoparticles and (3) $Al_2O_3$ insulating nanoparticles. The AC breakdown voltage of the oil samples is analysed using Weibull statistical analysis and the results reveal that the PFAE oil-based $Fe_3O_4$ nanofluid gives exceptional dielectric performance compared to other oil samples, whereby the AC breakdown voltage increases by 43%. It can be concluded that the PFAE oil-based $Fe_3O_4$ nanofluid is a promising dielectric liquid to substitute mineral oils.

• 전기학회논문지
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• 제65권10호
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• pp.1688-1693
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• 2016

In this study shall investigate the influence upon the electrical property of transformer oil due to the heat among accelerated heat degradation experiment for a constant hour in the typical insulation oils of mineral base oil, silicon base oil and vegetable oil. In addition, the electric insulation performance of insulation materials in transformer shall be evaluated through the electric property analysis according to the heat degradation of epoxy insulation material, which has been used for electric facilities such as a molded transformer.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1998년도 춘계학술대회 논문집
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• pp.203-206
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• 1998

In this paper, specimens stirred with the several kinds of benzotriazole(following as BTA) addition which is very effective to decrease the streaming electrification, are tested to investigate the change of properties for insulating fluid using in ultra-high voltage transformer, and it will give a guideline to find out a proper quantity of BTA addition for the most effective suppression against the streaming electrification. In GC, we could not find out the change of the physical properties in an insulating fluid by BTA. In a flowing transformer oil, the characteristics on dielectric of specimen contained BTA 10[ppm] are superior to the others.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1988년도 추계학술대회 논문집 학회본부
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• pp.241-245
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• 1988

This paper reports the experiments regarding to diagnosis techniques for power transformers by measuring dissipation factor and moisture contents of mineral oils. Thermal aging environments of mineral oils were varied by the specially designed systems. Thermal aging of elevated temperature of $90^{\circ}C$ was performed for about 240 and 460 hours, respectively. Dissipation factor, permittivity, and water content were measured. Our test samples were not exposed to air. Dissipation factor increased while permittivity did not change. The level of dissipation factor determining the insulating quality of mineral oil was compared with the previous results of resistivity and several correction factor.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.300-303
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• 2008

In the present study, the simple form of the heat transfer equation were suggested to estimate the temperature variation inside the oil pipe in order to determine the thickness of the insulating materials to retain the working oils below the critical temperature. The conservation of the thermal energy at arbitrary time were modeled to one dimensional unsteady equation with the empirical formula or data. The calculating results for non-insulation case showed that the temperature were very sensitive to the thermal convection by the velocity of the external wind. For insulation case, the insulation material which has higher density and specific heat, lower thermal conductivity should be chosen with more brighter coloring outside the pipe in order to retain the working oils below the critical temperature.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 추계학술대회 논문집 학회본부
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• pp.273-275
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• 1996

In order to investigate the electrical properties of naphthanic transformer oils for insulating and cooling, the characteristics for breakdown in temperature range of $20{\sim}100[^{\circ}C]$, that of AC breakdown in 1.0[mm] of gap length were made researches. As a result the characteristics for AC breakdown, it is confirm that the dielectric strength was increased to 6[ppm], 9[ppm] but decreased to 3[ppm].

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 추계학술대회 논문집 Vol.14 No.1
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• pp.605-608
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• 2001

With the intention of investigating the breakdown properties of oil-immersed transformer oils in temperature range of $20\sim100[^{\circ}C]$, we are made researches AC breakdown in the gap of $500\sim2500[{\mu}m]$. The classification for the physical properties of oil for oil-immersed transformer by FTIR and H-NMR experiments was confirmed to type of mineral oils. As the dependance of breakdown properties due to electrode gap length variation, breakdown voltage was found increasing according to the increase of gap, while dielectric strength was decreasing. As a result the characteristics for AC breakdown, It goes to prove that the breakdown voltage was increased to $90[^{\circ}C]$ but decreased over $90[^{\circ}C]$ in the temperature range. Also, breakdown voltage was found increasing in the increase of gap and the rising of temperature according to Weibull distribution.

• 공업화학
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• 제25권3호
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• pp.254-261
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• 2014

변압기 내부에서 발생한 열의 냉각과 절연의 목적으로 채워지는 전기절연유는 광유가 널리 이용되고 있지만, 유출 시야기되는 환경오염 문제와 열적 불안정성 등의 문제가 있다. 친환경적이고 넓은 온도 범위에서 사용 가능한 전기절연유를 합성하기 위해, 디글리세롤과 두 종류의 지방산을 반응시켜 diglycerol ester를 합성하였다. 서로 다른 특성을 가진 올레산과 카프릴산의 몰비에 따른 절연특성을 분석한 결과, 지방산의 몰비가 Oleic acid:Caprylic acid = 1:3일 때 유동점은 $-50^{\circ}C$, 인화점은 $306^{\circ}C$로 가장 우수한 절연특성을 보였다. 또한, 합성물은 지방산의 전환율이 상승할수록 인화점은 상승하고 유동점은 감소하였다. $SO_4{^{2-}}/ZrO_2$의 소성온도에 따른 촉매특성 및 전환율을 살펴본 결과, $600^{\circ}C$에서 소성한 $SO_4{^{2-}}/ZrO_2$가 결정성을 가지면서 비표면적 당 산점의 밀도가 높아 가장 높은 전환율을 보였다. 합성한 diglycerol ester는 식물성 절연유와 비교했을 때 전반적으로 식물성 절연유보다 우수한 특성을 보였다.