• Progress in Superconductivity and Cryogenics
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• v.5 no.2
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• pp.46-50
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• 2003

In the dielectric insulation design of any high temperature superconducting (HTS) apparatus as well as HTS fault current limiter in the electrical power systems, the breakdown characteristics of cryogenic coolants such as liquid nitrogen ($LN_2$) are an important factor of the insulating engineering. Previous reports concerned with the breakdown characteristics of liquid nitrogen have pointed out that bubbles and gaseous nitrogen have a treat influence on their breakdown phenomena, However, useful data for practical insulation design of HTS fault CUITent limiter operating at subcooled L$N_2$ have not been obtained enough. Therefore, this paper presents an experimental investigate of breakdown phenomena in liquid nitrogen under AC voltage, And, we observed the breakdown voltage (BDV) of liquid nitrogen with lowering temperature. The Weibull plots of the breakdown voltage of subcooled $LN_2$ for the needle-plane electrode with d= 10 mm are studied, The dependence of breakdown voltage for needle-plane and pancake coil-pancake coil electrode on temperature is illustrated, The relationship between the AC breakdown characteristics and the temperature were clarified.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.3
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• pp.280-285
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• 2023

A breakdown voltage and breakdown electric field of the transformer insulating oil of liquid dielectric were studied in uniform electric field and non-uniform electric field and the transformer insulating oil was observed by the process reached breakdown. Insulation performance evaluation of the liquid dielectric was evaluated at the electrode spacing of 2.5 mm under the conditions of domestic and international standards (KS C IEC 60156), so a comparative review was conducted at the electrode spacing of 2.5 mm. When the electrode spacing is 2.5 mm, the average breakdown voltage is 38.5 kV for sphere-sphere electrodes, 26.6 kV for plate-plate electrodes, 22.9 kV for needle-needle electrodes, and 24.3 kV for sphere-needle electrodes. 23.7 kV for the sphere-plate electrode, and 20.7 kV for the needle-plate electrode. From these results, it can be seen that the average value of the breakdown voltage at the electrode spacing of 2.5 mm, in ascending order, is sphere-sphere, plate-plate, sphere-needle, sphere-plate, needle-needle and needle-plate. It was found that the breakdown voltage of the unequal field was lower than that of the equal field.

• Journal of the Korean Ceramic Society
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• v.24 no.4
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• pp.392-396
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• 1987

Pure barium titanate was sintered at $1340^{\circ}C$ for 2, 4, 8, 16 hr to control their grain size. The measurements of breakdown strength and partial discharge characteristics were performed under rising AC voltage(60Hz). With increase of sintering time, the average grain size was increased and breakdown strength was slightly decreased. Partial discharge in pores was observed under high voltage, and a model of dielectric break down in barium titanate ceramics is proposed.

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1585-1587
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• 1996

The dielectric properties of DGEBA/MDA/GN system under inhomoneous electric field were investigated. As GN contents increased, impact strength increased, but dielectric breakdown strength decreased. At $150^{\circ}C$, the dielectric breakdown strength decreased and uniformly maintained with the increment of distance between two electrodes. The life-time of epoxy resin increased with the decrement of applied voltage, but dielectric breakdown didn't occur below specific applied voltage.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1990.10a
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• pp.102-104
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• 1990

In this paper, we studied and investigated as to temperature dependence of dielectric breakdown properties, and the dielectric breakdown properties, and deterioration-proof properties due to interface treatment effect. In the result, we knew that temperature dependence of dielectric breakdown strength due to filler content was decreased, identified that D.C. dielectric breakdown strength was improved at the filler content 50[%]. When the D.C. voltage was applied to the non silane and silane treated specimens deal with mechanical deterioration, the dielectric breakdown strength was improved at the 150[%].

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.10
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• pp.1471-1476
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• 2012

A study on the dielectric characteristics of the Glass Fiber Reinforced Plastic (GFRP) is important for designing a reliable high voltage superconducting machines such as transmission superconducting fault current limiters, superconducting cables, and superconducting transformers. In this paper, dielectric experiments of the GFRP under lightning impulse voltage are conducted in liquid nitrogen($LN_2$) according to various experimental conditions such as the thicknesses of the GFRP, the diameters of electrode systems and the pressures. The dielectric characteristics of the GFRP are analyzed by using a Finite Elements Method(FEM) according to various field utilization factors. It has been reported that the electrical insulation design of the GFRP would be conducted by considering the mean electric field intensity($E_{mean}$) distributed inside the GFRP. In this study, it is found that the dielectric performance of the GFRP could be explained by not only $E_{mean}$ but also the maximum electric field intensity ($E_{max}$). Finally, the empirical formulae of the GFRP to estimate an electrical breakdown voltage at sparkover under the lightning impulse condition are deduced. It is expected that the presented experimental results in this paper are helpful to design electrically reliable high voltage superconducting machines using the GFRP as an insulation material.

• Proceedings of the KIEE Conference
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• 1994.11a
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• pp.284-286
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• 1994

This paper describes the dielectric characteristics of $SF_6$ gas in non-uniform electric filed under lightning under lightning impulse and oscillating impulse voltages. The breakdown voltage-time characteristics and the breakdown voltage-pressure characteristics are measured over a pressure range extending from 0.1 to 0.5 [MPa] fur the coaxial electrode with a needle protrusion. The curvature radius of needle protrusion is 0.3[mm]. Also, the growth of the predischarge is simultaneously observed. As a result the polarity effect is pronounced, and the breakdowns voltage under the oscillating impulse voltage are higher than those under the lightning impulse voltage. It is found that the breakdown mechanism md predischarge phenomena ate closely related with the polarity and waveforms of the testing voltage.

• Journal of the Korean institute of surface engineering
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• v.57 no.1
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• pp.8-13
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• 2024

Anodizing of Al6061 alloy was conducted in two different electrolytes of 20% sulfuric acid and 8% sulfuric acid + 3 % oxalic acid solutions at a constant current or decreasing current density conditions, and its dielectric breakdown voltage was measured. The surface morphology of anodic oxide films was observed by TEM and thermal treatment was carried out at 400 ℃ for 2 h to evaluate the resistance of the anodic oxide films to crack initiation. The anodic oxide film formed in 8% sulfuric acid + 3 % oxalic acid solution showed higher dielectric breakdown voltage and better resistance to crack initiation at 400 ℃ than that formed in 20% sulfuric acid solution. The dielectric breakdown voltage increased 6 ~12% by applying decreasing current density comparing with a constant current density.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11b
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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.

• Transactions on Electrical and Electronic Materials
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• v.4 no.4
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• pp.13-17
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• 2003

This paper deals with the edge effect in thin insulating films, focusing on their dependence on film thickness. The finding is that the electric field is lowered at the edge as the film thickness is reduced, which, in turn, is closely related to dielectric breakdown voltage. In order to analyze this phenomenon, a simple capacitor model is introduced with which dependence of dielectric breakdown voltage around the electrode edge on the film thickness is explained. Due to analytical difficulty to get the expression of electrical field strength at the edge, an equivalent circuit approach is used to find the voltage expression first and then the electric field expression using it. The relation gets to an agreement with the experimental findings shown in the paper. This outcome may be extended to solve similar problems in multi-layer insulating films.