• Transactions on Electrical and Electronic Materials
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• 제8권6호
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• pp.278-282
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• 2007

In the complex insulation system that is used in extra high voltage(EHV) devices, according to the trend for electric power equipment of high capacity and reduction of its size, macro interfaces between two different bulk materials which affect the stability of insulation system exist inevitably. In this paper, the dielectric strength decrease of the macro interfaces between epoxy and ethylene propylene diene terpolymer(EPDM) was estimated by using the applied voltage to breakdown time characteristics. Firstly, the AC short time dielectric strength of specimens was measured at room temperature. Then, the breakdown time was measured under the applied constant voltage which is 70% of short time breakdown voltage. With these processes, the life exponent n was determined by inverse power law, and the long time breakdown voltage can be evaluated. The best condition of the interface was LOS(low viscosity(350 cSt) silicone oil spread specimen). When 30 years last on the specimens, the breakdown voltage was estimated 44% of the short time breakdown voltage.

• Journal of Electrical Engineering and Technology
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• 제6권3호
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• pp.391-396
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• 2011

The tracking pattern formed on the dielectric surface due to a surface electrical discharge exhibits fractal structure. In order to quantitatively investigate the fractal characteristics of the surface tracking pattern, the dielectric breakdown model has been employed to numerically generate the surface tracking pattern. In dielectric breakdown model, the pattern growth is determined stochastically by a probability function depending on the local electric potential difference. For the computation of the electric potential for all points of the lattice, a two-dimensional discrete Laplace equation is solved by mean of the successive over-relaxation method combined to the Gauss-Seidel method. The box counting method has been used to calculate the fractal dimensions of the simulated patterns with various exponent $\eta$ and breakdown voltage $\phi_b$. As a result of the simulation, it is found that the fractal nature of the surface tracking pattern depends strongly on $\eta$ and $\phi_b$.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제49권3호
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• pp.152-158
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• 2000

This paper deal with the experimental discussion about the impulse and AC dielectric strength of SF6 gas insulated transformer. Test sample is measured the dielectric breakdown voltage about modeling of the first and second section which is the weakest for surge voltage. The AC breakdown voltage is appeared 1.4 times than impulse breakdown voltage, so we can estimate that the impulse breakdown voltage is severe to AC breakdown voltage, and when the impulse is applied, in case of lmm tapping with Nomex paper, the characteristics of dielectric breakdown voltage is same to that in oil immersed transformer when SF6 gas pressure is 2.2kg/$cm^2$G.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1993년도 정기총회 및 추계학술대회 논문집 학회본부
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• pp.216-218
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• 1993

XLPE cable accessories are mainly consisted by the combination of various insulating materials such as XLPE cable insulation, rubber, epoxy, etc. It is important to investigate the dielectric and breakdown characteristics of the interfaces between various insulating materials. In this paper, by testing and measuring the breakdown strength, dissipation factor, volume and surface resistance and conduction current of specimens, we report the dielectric and breakdown characteristics of interfaces between various insulating materials.

• Transactions on Electrical and Electronic Materials
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• 제11권6호
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• pp.261-265
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• 2010

In this paper, we attempt to improve the electrical characteristics of epoxy resin at high temperature (above $80^{\circ}C$) by adding magnesium oxide (MgO), which has high thermal conductivity. Scanning electron microscopy (SEM) of the dispersion of specimens with added MgO reveals that they are evenly dispersed without concentration. The dielectric breakdown characteristics of $SiO_2$ and MgO nanocomposites are tested by measurements at different temperatures to investigate the filler's effect on the dielectric breakdown characteristics. The dielectric breakdown strength of specimens with added $SiO_2$ decreases slowly below $80^{\circ}C$ (low temperature) but decreases rapidly above $80^{\circ}C$ (high temperature). However, the gradient of the dielectric breakdown strength of specimens with added MgO is slow at both low and high temperatures. The dielectric breakdown strength of specimens with 0.4 wt% $SiO_2$ is the best among the specimens with added $SiO_2$, and that of specimens with 3.0 wt% and 5.0 wt% MgO is the best among those with added MgO. Moreover, the dielectric strength of specimens with 3.0 wt% MgO at high temperatures is approximately 53.3% higher than that of specimens with added $SiO_2$ at $100^{\circ}C$, and that of specimens with 5.0 wt% of MgO is approximately 59.34% higher under the same conditions. The dielectric strength of MgO is believed to be superior to that of $SiO_2$ owing to enhanced thermal radiation because the thermal conductivity rate of MgO (approximately 42 $W/m{\cdot}K$) is approximately 32 times higher than that of $SiO_2$ (approximately 1.3 $W/m{\cdot}K$). We also confirmed that the allowable breakdown strength of specimens with added MgO at $100^{\circ}C$ is within the error range when the breakdown probability of all specimens is 40%. A breakdown probability of up to 40% represents a stable dielectric strength in machinery and apparatus design.

• 한국초전도ㆍ저온공학회논문지
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• 제5권2호
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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.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 추계학술대회 논문집 Vol.14 No.1
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• pp.597-600
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• 2001

In order to investigate the electrical properties of X-ray tube oils for insulating and cooling, the breakdown characteristics in temperature range of $20\sim100[^{\circ}C]$, that of AC breakdown in 0.5~2.5[mm] of gap length, we are made researches. The classification for the physical properties of oil for X-ray tube by FTIR and H-NMR experiments was confirmed to type of mineral oils. As for the dependance of breakdown characteristics due to electrode gap length, breakdown voltage was found nearly uniform by impurity effect according to the increase of gap. As a result the characteristics for AC breakdown, the dielectric strength was increased to $90[^{\circ}C]$ but decreased over $90[^{\circ}C]$ in the temperature range.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 추계학술대회 논문집
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• pp.597-600
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• 2001

In order to investigate the electrical properties of X-ray tube oils for insulating and cooling, the breakdown characteristics in temperature range of 20∼100[$^{\circ}C$], that of AC breakdown in 0.5∼2.5(mm) of gap length, we are made researches. The classification for the physical properties of oil for X-ray tube by FTIR and $^1$H-NMR experiments was confirmed to type of mineral oils. As for the dependance of breakdown characteristics due to electrode gap length, breakdown voltage was found nearly uniform by impurity effect according to the increase of gap. As a result the characteristics for AC breakdown, the dielectric strength was increased to 90[$^{\circ}C$] but decreased over 90[$^{\circ}C$] in the temperature range.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1987년도 정기총회 및 창립40주년기념 학술대회 학회본부
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• pp.477-479
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• 1987

An understanding of dielectric breakdown characteristics in cryogenic liquids is of importance in the development of various cryogenic and superconducting electrical equipments. This investigation describes measurements of pulse breakdown voltage, polarity effect, conditioning effect and time lag characteristics of cryogenic liquids.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1990년도 하계학술대회 논문집
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• pp.275-278
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• 1990

This study investigated electrical characteristics of solid and liquid epoxy rosins by measuring dielectric breakdown and dielectric loss when epoxy resins were exposed to a mixing cure, i.e., Fusion Blend Method. It was found that mixing epoxy resins were superior to dielectric breakdown and has shorter curing time compare with those of pure liquid epoxy resins.