• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.9
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• pp.793-797
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• 2007

In this paper, the long time breakdown characteristic of the epoxy composite, which is widely used in the insulation system for high voltage application, was estimated with Weibull distribution. In the procedure of the estimation, the short time breakdown characteristics for the epoxy composite specimens, which were made with the variation of hardener and/or filler, were tested firstly. Then the long time voltage-to-time test was implemented. Finally, the long time breakdown voltage of each specimen was estimated with the parameters obtained from the statistical treatment with Weibull distribution. Base on the results, it has been found that the optimal weight ratio of epoxy resin/hardener/filler that has the excellent long time breakdown characteristic was 100/100/65. It was due to the silane treatment which relieves the electric field at the interface between filler and epoxy.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07a
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• pp.439-442
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• 2002

The interface between two different materials in the insulation systems is the weak-link in the underground power transmission systems, In this paper, Optimum conditions of the interface between Epoxy and EPDM is studied. The variation factor condition of interface is roughness of surface, spreading of oils, interfacial pressure and temperature. The breakdown times under the constant voltage below the breakdown voltage were also gained. The breakdown voltage at the after laying time equivalent to is calculated by the V-t characteristic and the inverse power law. When this is done, the characteristic life exponent n is used and the long time breakdown voltage can be evaluated.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.11
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• pp.1003-1008
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• 2002

In this paper, the estimation of lifetime with the various conditions of the interface between toughened epoxy and rubber which are consisting materials of underground power delivery system has been studied. After the measurement of the short time AC interfacial breakdown strength on macro interfaces at room temperature, the breakdown time at several voltages were measured under the constant voltages lower than the short time breakdown voltage. The long time breakdown voltage was calculated by using Inverse Power Law. Two types of interfaces was studied. One was the interface between toughened epoxy and EPDM(Ethylene Prorylene Diene Terpolymer). The other was the interface between toughened epoxy and silicon rubber. Interfacial pressure and roughness of interfaces was determined through the characteristic of short time AC interfacial breakdown strength. Oil condition was no oiled, low viscosity oiled and high viscosity oiled. High viscosity oiled interface between Toughened epoxy and silicon rubber had the best lifetime exponent, 20.69. and the breakdown voltage of this interface after 30 years was evaluated 19.27㎸.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.7
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• pp.607-611
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• 2000

The characteristics on the interface between Epoxy and EPDM which are materials of the underground insulation systems of power delivery have studied. The breakdown strength of specimens are observed by applying high AC voltage at the room temperature. The breakdown times under the constant voltage below the breakdown voltage were gained. As constant voltage is applied the breakdown time is proportion to the breakdown strength. The life exponent n is gained by inverse power law and the long breakdown life time can be evaluated. AC breakdown strength and life time is improved by oiling to the interface. When the low viscosity oil is spread interface has the highest life time.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1978-1980
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• 2000

Because the interfaces between two different materials are the weak-link in the underground power transmission systems, they affects the stability of insulation systems. In this paper, Epoxy/EPDM interface is selected and investigated the optimum condition by variation of interfacial conditions such as roughness of surface, spreading of oils, interfacial pressure and temperature. The breakdown times under the constant voltage below the breakdown voltage were also gamed. The breakdown voltage at the after laying time equivalent to is calculated by the V-t characteristic and the inverse power law. When this is done. the characteristic life exponent n is used and the long time breakdown voltage can be evaluated.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.50 no.9
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• pp.456-465
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• 2001

In this paper, breakdown voltages in $SF_6-N_2$ mixtures were experimentally investigated to understand characteristics of dielectric strength and physical phenomena in nonuniform field disturbed by a needle shape protrusion. The test voltages are the lightning impulse$(\pm1.2/44 \mus)$ and the damped oscillatory impulse$(\pm400 ns / 0.83 MHz)$ voltages which can be occurred by the operation of disconnecting switches in gas-insulated switchgears(GIS). The effects of the polarity and wave shape of the test voltages, and the gas pressure on the V-t characteristics were in detail examined. The V-t characteristic curves were measured in different two ways : (1) one is the method by taking the maximum voltage recorded at or prior to breakdown against the time to breakdown, that is, the Procedures recommended in IEC 60060-1, (2) the other is the method by taking the voltage at the instant of chopping against the time to breakdown. As a result, the V-t characteristics of $SF_6-N_2$ mixtures in nonuniform electric field were significantly affected by the polarity and wave shape of the applied voltages. The positive breakdown voltages resulted in lower breakdown voltages in the time ranges considered, and the V-t curves for the negative oscillatory impulse voltage were extended over the longer time range. For the lightning impulse voltages, the V-t curves obtained by IEC Pub. 60060-1 were nearly same with the V-t curves obtained by the voltage at the instant of chopping against the time to breakdown. It is clear that the actual breakdown voltages were much lower than the maximum voltages appearing at or prior to breakdown because of the displacement current produced as a result of the dV/dt during the oscillatory transient voltage app1ication. The scattering of the negative actual breakdown voltages was much larger than that of the positive.

• 전기의세계
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• v.30 no.6
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• pp.357-365
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• 1981

When electronegative gas SF$_{6}$ is dissolved and charged with insulating oil, the effect caused in the process by electronegative characteristic is studied and also the pressure effect caused by electronegative SF$_{6}$ acting on the liquid-level is examined respectively. When inert gas Ar is used to find a pressure effect acting on the liquid-level, its effect on dielectric strength is considered in the experiment. With three kinds of impulse voltage different in the duration of wave front and wave tail, a brief experiment if carried out ot see the effects on the dielectric breakdown characteristic as the wave is changing; either if I$_{2}$ and SF$_{6}$ are added to the insulating oil, or if the oil pressure is increased by Ar the dielectric strength becomes great and the longer the duration of wave front is, the greater the increase of the breakdown voltage, because I$_{2}$ added by a small quantity brings about some hirderance in the formation of gas phase. Likewise, the greater the changed pressure is, the greater the incerase of the breakdown voltage. When SF$_{6}$ is charged, the electronegative characteristic is prevailing at the time of low balanced pressure, and the pressure effect at the time of high balanced pressure.ressure.

• Proceedings of the KIEE Conference
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• 1997.07e
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• pp.1770-1772
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• 1997

In this paper, Voltage-time characteristics of lightning impulse and switching surge breakdown in SF6 is studied on the gap and various pressure. The characteristics is categorized into three pattern depending on the configuration of the gap and gas pressure. The properties of the voltage-time characteristics in these patterns are generalized as semi-empirical formula which will be useful in the quantitation voltage evaluation of insulation coordination and the abnormal voltage protection of SF6 insulated power equipment.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.04b
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• pp.8-9
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• 2008

In the procedure of the estimation, the short time breakdown characteristics for the epoxy composite specimens, which were made with the variation of hardener and/or filler, were tested firstly. Then the long time voltage-to-time test was implemented. Finally, the long time breakdown voltage of each specimen was estimated with the parameters obtained from the statistical treatment with Weibull distribution. Base on the results, it has been found that the optimal weight ratio of epoxy resin/hardener/filler that has the excellent long time breakdown characteristic was 100/100/65. It was due to the silane treatment which relieves the electric field at the interface between filler and epoxy.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.8
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• pp.445-450
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• 2000

Many successful developments and microscopic studies have been made on the high quality insulating materials. However, a little attention have given to the macroscopic interface in HV(High Voltage) insulating systems. In this study, AC interfacial breakdown strength and V-t characteristic of the interface between Epoxy/EPDM(ethylene propylene diene terpolymer) are investigated. Electrode system is designed to reduce the charges from electrodes and to have the tangential potentials along the interface between Epoxy/EPDM by FEM(finite elements method). The AC breakdown strength is observed when HV is given to the interface. It is shown that AC interfacial breakdown strength is improved by increasing interfacial pressure and oiling. In particular, it was saturated at certain interfacial pressure level. V-t characteristic is able to extend to the life time of the interface between Epoxy/EPDM. Oiling also plays a good roll in prolongation of the life time.