• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.12
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• pp.1118-1123
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• 2008

High voltage multilayer ceramic capacitors (MLCCs) are classified into two classes-those for temperature compensation (class I) and high dielectric constant materials (class II). We manufactured high voltage MLCC with temperature coefficient characteristics of C0G and X7R and studied the characteristics of electric properties. Also we studied the characteristics of dielectric breakdown voltage (V) as the variation of thickness in the green sheet and how to pattern the internal electrodes. The dielectric breakdown by electric field was caused by defects in the dielectric materials and dielectric/electrode interface, so the dielectric thickness increased, the withstanding voltage per unit (E) thickness decreased. To overcome this problem, we selected the special design like as floating electrode and this design affected the increasing breakdown voltage(V) and realized the constant withstanding voltage per unit thickness(E). From these results, high voltage application of MLCCs can be expanded and the rated voltage can also be develop.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.8
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• pp.685-689
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• 2005

In the fabrication and design of MLCCs (Multilayer Ceramic Capacitors) with Ni inner electrode for medium and high voltage, reliability and dielectric breakdown mode have been investigated. For thickness of green sheet, the relationship between the rated voltage versus the thickness of green sheet. Increasing the thickness of green sheet increases the dielectric breakdown voltage. However, a practical limit to this linear relationship occurs at 30 urn and above. As the thickness of green sheet increased, dielectric breakdown voltage and weibull coefficient is increased, but abruptly decrease at 30 urn and 36 urn. When 24 urn of green sheet thickness, weibull coefficient and dielectric breakdown voltage were 13.58 and 70 V/um respectively. The results enabling the MLCCs to demonstrate high levels of reliability at medium and high voltage.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.49 no.3
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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.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.1
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• pp.39-44
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• 1999

The dielectric layers in AC plasma display panel(PDP) are essential to the discharge cell structure, because they protect metal electrodes from sputtering by positive ion bombarding in discharge plasma and form a sheath of wall charges which are essential to memory function of AC PDP. This layer should have high dielectric breakdown voltage, and also be transparent because the luminance of PDP is strongly correlated this layer. In this paper, we discussed the dielectric breakdown voltage and transparency of the dielectric layer under various conditions. As a result, on the $15\mum$ thickness, the minimum dielectric breakdown voltage was 435V and the transmission coefficient was about 80% after $570^{\circ}C$ firing process. It can be proposed that the resonable dielectric thickness in AC PDP is $15\mum$ because it has about 75V margin on the maximum applied voltage.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.5
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• pp.1005-1010
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• 2011

The accidents caused by dielectric instability have been increasing in power grid. It is important to enhance the dielectric reliability of a high voltage apparatus to reduce the damage from electrical hazards. To develop an electrically reliable high voltage apparatus, the experimental study on the electrical breakdown field strength is indispensable, as well as theoretical approach. In this paper, the lightning impulse breakdown characteristics considering utilization factors are studied for the establishment of insulation design criteria of an high voltage apparatus. The utilization factors are represented as the ratio of mean electric field to maximum electric field. Dielectric experiments are performed by using several kinds of sphere-plane electrode systems made of stainless steel. As a result, it is found that dielectric characteristics are affected by not only maximum electric field intensity but also utilization factors of electrode systems. The results are expected to be applicable to designing the air-insulated high voltage apparatuses.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.6
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• pp.821-826
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• 2012

The streaming electrification process of vegetable insulating oils occurring when the oils contacted with solid material in a high power transformer circulation system seems to cause electrical discharge incidents and may cause failures. We therefore measured the dielectric breakdown voltage tendency of vegetable insulating oils flowing on the surface of the charging device with various velocity and temperature. First, the relation between the velocity and breakdown voltage tendency of vegetable oils, can be explained by volume effect and v-t effect. Second, experimental results show that applied voltage have little effect on dielectric breakdown voltage, when vegetable insulating oils used for large power transformer.

• Transactions on Electrical and Electronic Materials
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• v.8 no.6
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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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• v.9 no.1
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• pp.280-285
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• 2014

In order to evaluate the insulation deterioration in the stator windings of five gas turbine generators(137 MVA, 13.8 kV) which has been operated for more than 13 years, diagnostic test and AC dielectric breakdown test were performed at phases A, B and C. These tests included measurements of AC current, dissipation factor, partial discharge (PD) magnitude and capacitance. ${\Delta}I$ and ${\Delta}tan{\delta}$ in all three phases (A, B and C) of No. 1 generator stator windings showed that they were in good condition but PD magnitude indicated marginally serviceable and bad level to the insulation condition. Overall analysis of the results suggested that the generator stator windings were indicated serious insulation deterioration and patterns of the PD in all three phases were analyzed to be internal, slot and spark discharges. After the diagnostic test, an AC overvoltage test was performed by gradually increasing the voltage applied to the generator stator windings until electrical insulation failure occurred, in order to determine the breakdown voltage. The breakdown voltage at phases A, B and C of No. 1 generator stator windings failed at 28.0 kV, 17.9 kV, and 21.3 kV, respectively. The breakdown voltage was lower than that expected for good-quality windings (28.6 kV) in a 13.8kV class generator. In the AC dielectric breakdown and diagnostic tests, there was a strong correlation between the breakdown voltage and the voltage at which charging current increases abruptly ($P_{i1}$, $P_{i2}$).

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.431.2-431.2
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• 2014

The dielectric breakdown voltage (DBV) is a measure of an insulating fluids ability to withstand a high electric field stress without breaking down. Conventionally, the presence of water or particulate matter in a dielectric fluid comprises the liquid's breakdown strength. However, the addition of magnetic nanoparticles (MNPs) in the base oil can increase the dielectric breakdown voltage of the fluid reversely, if the condition of the added particles in the fluid is in balance with that of keeping down the initiation and propagation of electrical streamers. In this study, we developed a mathematical model by a set of coupled, nonlinear equations using the COMSOL multiphysics finite element simulation suite and calculated the dielectrophoretic activity of magnetic nanoparticles suspended in the presence of electric field, which is the behavior responsible for enhancing the dielectric characteristics of transformer oil, in order to examine how the activity differ in a transformer oil-based magnetic fluid.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1538-1539
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• 2011

In this study, we have investigated the dielectric breakdown by measuring AC (60Hz) breakdown strength of the fluids in accordance with IEC 156 standard and have compared the results with references. It was found that the dielectric breakdown voltage of pure transformer oil is around 12 [kV] with the gap distance of 1.5mm between electrodes. In case of our transformer oil based magnetic fluids with 0.1% < ${\Phi}$(volume concentration of magnetic particles) <0.6%, the dielectric breakdown voltage shows above 30 [kV], which is 2.5 times higher than that of pure transformer oil. It can be explained by the changed ionization process by adding nanoparticles in pure transformer oil, which is due to trapped fast electrons and slow negative nanoparticles. Moreover, in case of the fluid with applied magnetic field, the dielectric breakdown voltage increases above 40 [kV], which is 3.3 times higher than that of pure transformer oil.