• Proceedings of the KIEE Conference
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• 1999.07e
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• pp.2066-2068
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• 1999

In this paper, an optical fiber sensor(OF sensor) utilizing the principal of Sagnac interferometer was proposed to detect the discharge signals which generated from needle-sphere electrode system in insulating oil. The performance of OF sensor was checked by sinusoidal calibration signal generated by PZT acuator at 198kHz. The detected discharge signals consisted of acoustic signal and the electrical noise. The noise signal could be removed by digital low pass filter. It was demonstrated that the OF sensor in this research had a possibility to detect the discharge signals in power apparatus.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.11
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• pp.622-626
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• 2000

In this paper, an optical fiber sensor(OF sensor) utilizing the principal of Sagnac interferometer was proposed to detect the discharge signals. The needle-sphere electrode system in insulating oil generated the signals. The performance of OF sensor was checked by sinusoidal calibration signal generated by PZT actuator at 198KHz. The detected discharge signals consisted of acoustic signal and the electrical noise. The noise signal could be removed by digital low pass filter. It was demonstrated that the OF sensor in this research had a possibility to detect the discharge signals in power apparatus.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.11a
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• pp.225-228
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• 1997

The main fault in this interface is that power cable insulating materials are mainly composed of a double layered structure, XLPE/FPDM laminates in cable joint. In this parer, we instituted the interface of XLPE/EPDM laminates and then investigated the breakdown and conduction characteristics as a function of heat treatment time. The results showed that conduction current was influenced by volatile crosslinking by-products which remained inside the insulating material during the production of XLPE and EPDM, especially during heat treatment process. And conduction current of XLPE/Oil 12500cSt/EPDM was more stable than XLPE/Grease/EPDM from the long heat treatment time. AC breakdown strength of silicone oil itself from the heat treatment was changed during the 4∼12 hour heat treatment time.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.136-136
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• 2016

Commonly used oil-based polymer resin has environmental and safety issues. Many researches for replacing the harmful solvent-borne resins to water-borne resins have been investigated to purify harmful environmental resources and follow the export and import of hazardous materials regulations. In this research, ultrasonic spray coatings of aqueous polymer resin were studied to fabricate thin insulating layer (${\sim}{\mu}m$) on the rectangular copper wire. It needs to have appropriate wettability between resin and substrate during the ultrasonic spray coating process to coat aqueous polymer uniformly. Furthermore, stabilities of coating solution and fabricating process are required to form thin insulating layer on the substrate. In here, physical characteristics such as viscosity of 6 types of commercial polymer dispersions and emersions were analyzed to confirm compatibility for ultrasonic spray coating process. These resins were dissolved in isopropyl alcohol, used for true solvent, and were diluted with ethanol, utilized for diluent. Also, solubilities, dispersion characteristics, and viscosities of these diluted polymer resin solutions were confirmed. Dispersion characteristic and viscosity of coating solution affects jetting of ultrasonic spray coating and these jetting characteristics influence morphologies of insulating layer. In conclusion, we have known that aqueous polymer solution should have outstanding dispersion characteristic and certain range of viscosity to fabricate thin polymer insulating layer uniformly with ultrasonic spray coating.

• Journal of the Korean Society of Safety
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• v.19 no.1
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• pp.56-59
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• 2004

In this paper, we investigated the influence of gap length and tip radius on breakdown of mineral based insulation oil. Applied voltages were DC and AC voltage. Electrode system was needle-plane structure. The tip radius of needle electrode was 5, 10, 20 and 25${\mu}m$, respectively. We measured breakdown voltage for each of tip radius with increasing electrode gap, 2mm to 12mm. Electric breakdown strength at tip was calculated using Mason's equation contained geometric figure. As gap length increased, breakdown strength increased linearly. But, as tip radius of needle increased, breakdown strength decreased exponentially. It can be explained by the phenomenon that electron is easily injected, as tip radius increases, and effective work function decreases. When appling DC voltage, breakdown strength was higher when polarity of needle was negative than positive. It is because of the space charge effect in accordance with the influence of liquid motion.

• Proceedings of the KIEE Conference
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• 1992.07b
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• pp.931-933
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• 1992

The static charges generated at the interface between the insulating oil and the solid materials, can be affected by impurities such as moisture. This paper investigated the charging tendency of clean oil and the oil with moisture in stainless steel pipe. The experimental results show that static electrification of the oil with moisture is smaller than that of the clean oil, and the oil is positively charged.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.12
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• pp.1136-1141
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• 2003

The primary insulation materials used in an oil filled transformer are kraft paper, wood, porcelain and oil. Modern transformers use chemically treated paper to improve its tensile strength and resistance to aging caused by immersion in oil. But these insulation papers are mainly aged by thermal stress. Over the life time of the insulation paper and oil, it is exposed to high temperatures, oxygen and water. Its interaction with the steel of the tank and core plus the copper and aluminium of the windings will eventually cause the chemical properties of the oil to decay. High temperature have an effect on mechanical strength of cellulous paper used in the layer insulation. We made two aging cells in which insulation papers and mineral oil are conducted to test thermal properties. It is measured dielectric strength, number of acid, moisture, etc. of insulation paper and oil aged in the aging cells.

• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1594-1596
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• 2001

The purpose of this paper is to provide the fundamental data which can be used for the design of pole transformers. For the purpose, electrical characteristics of aged mineral oil and silicone oil were analyzed by comparing with the results of virgin ones. For the experiment, an oil bath which can keep constant temperature was constructed to thermally deteriorate the specimens. And transformer materials were put together in the bath according to the their ratio in weight in the pole transformer. And the parameters such as relative permittivety, tan$\delta$ and specific resistance were measured. As a results, the permittivity of silicone oil was higher than that of mineral oil, and its decreasing rate with temperature was also higher. In addition, it was found that tan$\delta$ and specific resistance of virgin and aged oil began to differ at similar temperature.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11a
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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∼100[$^{\circ}C$], we are made researches AC breakdown in the gap of 500∼2,500[$\mu\textrm{m}$]. The classification for the physical properties of oil for oil-immersed transformer by FTH and $^1$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.

• Applied Chemistry for Engineering
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• v.25 no.3
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• pp.254-261
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• 2014

The transformer is a static electrical device that transfers energy by inductive coupling. Then, heat is occurred at coils, inner transformer was filled with insulating oils for cooling and insulation. Although mineral oil as insulating oil has been widely used, it does not meet health and current environmental laws because it is not biodegradable. Therefore, in this study, the diglycerol ester was synthesized with diglycerol and fatty acids (oleic acid and caprylic acid) over various catalysts for insulating oil having biodegradability, high flash points and low pour points. The sulfated zirconia ($SO_4{^{2-}}/ZrO_2$) catalyst prepared at different calcination temperature shows the highest conversion of fatty acids at $600^{\circ}C$ due to crystallinity and high density of acid sites per surface area. When the molar ratio of oleic acid and caprylic acid is 1:3, the diglycerol ester shows superior insulation properties that are the flash point of $306^{\circ}C$ and pour point of $-50^{\circ}C$. The insulation properties of synthesized diglycerol ester shows the pour point of $-50^{\circ}C$ and the flash point of over $300^{\circ}C$. Therefore, diglycerol ester is superior to the vegetable oils in insulation properties.