• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1532-1534
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• 1999

Electrical treeing phenomenon, regarded as pre-breakdown which accelerates aging process leading an insulation to the complete breakdown, is with no doubt extremely fatal to the performance of the insulation. Investigated in this paper is electrical treeing representing local dielectric failure according to flow pattern, the flow history of liquid polyethylene formed during the extrusion process. Experiments of electrical tree initiation by means of ramp tests were conducted using newly developed electrode system with point-to-point structure. Constant voltage tests were also carried out with the electrode system to estimate the life time of the insulation. Results were analyzed using statistical method such as Weibull distribution.

• Transactions on Electrical and Electronic Materials
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• v.13 no.2
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• pp.85-88
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• 2012

Studies on the effects of layered silicate content on the AC electrical treeing and breakdown behaviors of epoxy/layered silicate nanocomposites were carried out in needle-plate electrode geometry. Wide-angle X-ray diffraction (WAXD) analysis and transmission electron microscopy (TEM) observation showed that 1 wt% of the multilayered silicate was fully exfoliated into nano-sized monolayers in the epoxy matrix however, over 3 wt% of the silicate was in an intercalated state. When 1 wt% layered silicates were incorporated, an electrical tree was initiated in 439 min and propagated at a speed of 2.3 ${\mu}m$/min after applying 781.4 kV/mm, representing a decreased in starting initiation time by a factor of 11.0 and increase in propagation speed by a factor 8.2 in comparison with neat epoxy resin. These values were in great decline after the layered silicate content was increased to 3wt% which implies that the exfoliated silicate blocked the tree initiation and propagation processes effectively. However the effect was largely decreased in the intercalated state.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.41 no.9
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• pp.1060-1070
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• 1992

In this paper, characteristics of Acoustic Emission in Low Density Polyethylene were studied from tree initiation to breakdown under long-term inhomogeneous alternative electrical field. The voltage levels used were 9, 11 and 14[kV]. Especially, a newly developed automatic measuring system was used to measure time variations of AE average amplitude, AE pulse number, AE pulse distribution patterns due to polarities. The patterns wer specially the variated patterns, when tree propagated. Also, parameters for dielectric breakdown prediction, which were suggested by Okamoto, were calculated. The result was analysed by tree shapes and partial discharge activities in tree due to tree initiation and propagation.

• Transactions on Electrical and Electronic Materials
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• v.14 no.5
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• pp.278-281
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• 2013

The effects of electric field frequency on the AC electrical treeing phenomena in an epoxy/layered silicate (1.5 wt%) were investigated in a needle-plate electrode arrangement. A layered silicate was exfoliated in an epoxy-base resin with AC electric field apparatus. To measure the treeing initiation and propagation- and the breakdown rate, a constant alternating current (AC) of 10 kV with three different electric field frequencies (60, 500, and 1,000 Hz) was applied to the specimen in the needle-plate electrode specimen in an insulating oil bath at $130^{\circ}C$. At 60 Hz, the treeing initiation time was 12 min, the propagation rate was $0.24{\times}10^{-3}$ mm/min, and the morphology was a dense branch type. As the electric field frequency increased, the treeing initiation time decreased and the propagation rate increased. At 1,000 Hz, the treeing initiation time was 5 min, the propagation rate was $0.30{\times}10^{-3}$ mm/min, and the morphology was a dense bush type.

• Proceedings of the KIEE Conference
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• 1998.07d
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• pp.1337-1339
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• 1998

The trench termination scheme is introduced for high voltage devices. The curvature of the depletion region at field limiting ring is critical factor to determine the breakdown voltage. The smooth curvature of the depletion junction alleviate the electric field crowding effect around this region. In the trench field limiting ring, the radius of the depletion region is smaller than conventional field limiting ring, but the distance between every trench is spaced small enough to punchthrough before initiation of local breakdown. The trench field limiting ring on silicon can ne formed by RIE followed by oxidation on side wall surface of the trench, and polysilicon filling. The combined termination of this trench floating field ring and field plate have been designed and analyzed. The breakdown simulation by 2-dimensional TCAD shows that the cylindrical junction breakdown voltage for substrate doping might be 99 percent of the ideal breakdwon voltage for substrate doping concentration of $3\times10^{14}cm^{-3}$ with about $100{\mu}m$ of lateral termination width.

• 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.

• Journal of Electrical Engineering and Technology
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• v.5 no.2
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• pp.329-336
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• 2010

The paper describes the electrical and optical properties of underwater discharges in highly inhomogeneous electric fields caused by 1.2/50 ${\mu}s$ impulse voltages as functions of the polarity and amplitude of the applied voltage, and various water conductivities. The electric fields are formed by a point-to-plane electrode system. The formation of air bubbles is associated with a thermal process of the water located at the tip of the needle electrode, and streamer coronas can be initiated in the air bubbles and propagated through the test gap with stepped leaders. The fastest streamer channel experiences the final jump across the test gap. The negative streamer channels not only have more branches but are also more widely spread out than the positive streamer channels. The propagation velocity of the positive streamer is much faster than that of the negative one and, in fact, both these velocities are independent of the water conductivity; in addition the time-lag to breakdown is insensitive to water conductivity. The higher the water conductivity the larger the pre-breakdown energy, therefore, the ionic currents do not contribute to the initiation and propagation of the underwater discharges in the test conditions considered.

• 전기의세계
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• v.26 no.2
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• pp.57-65
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• 1977

In roder to investigate the influence of treeing on electric breakdown of solid organic insulator the initiation and growing mechanism of tree itself, and the correlation between corona discharge and treeing phenomena in solid orgainc insulating materials, several experiments were carried out by means of needle test on polymethyl-methacrylate. The obtained results showed that the existence of voids in specimen had important effects on initiation voltage of trees and, when the direct voltage was applied, the initiation voltage of trees increased by space charge effect. And also the stagnation phenomena due to the transfer of vacancy cluster or polymekr cage in specimen might beconsidered in process of growth of trees, and corona discharge seemed to be the pre-phenomena of treeing because trees were normally initiated by internal discharge in voids.

• 전기의세계
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• v.29 no.9
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• pp.577-583
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• 1980

This paper is intended to analyze the characteristics of breakdown of polyethylene dielectrics, which was caused by A.C. voltage after impulse fatigue, by using weibull distribution. The impact of impulse fatigue upon the accurance and development of tree and the impact of void upon treeing are investigated. From the results of experiment, it is found that the life of polyethylene subjected to impulse voltage is shorter than that not subjected to impulse voltage. And in the case of void existence, it's life comes to be short remarkably, and the breakdown is almost concentrated on its initiation. From the results observed by the microscope, it is found that the treeing phenomena varies according as whether impulse voltage was applied to polyethylene before being applied to A.C. voltage and whether polyethylene has void or not.

• Journal of Electrical Engineering and Technology
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• v.5 no.1
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• pp.156-162
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• 2010

This paper describes electrical and optical characteristics of discharge developments in water under inhomogeneous fields caused by impulse voltages. Predischarge current and discharge light images were observed for different water resistivities and applied voltages between the hemispherical water tank and the needle electrode. The electrical parameters characterizing discharge developments are analyzed based on the discharge light images and voltage-current (V-I) curves, and electrical resistances derived by voltage and current waveforms. As a result, when the streamer corona is initiated at the tip of the needle electrode, the transient resistance suddenly drops and V-I curves form a 'loop'. The length of streamer propagation is increased with increasing peak value of the applied voltage, and the streamer corona extension is enlarged with increasing water resistivity. The electrical resistances before streamer corona initiation are rarely changed by different applied voltages. On the other hand, the electrical resistances after streamer corona initiation are found to be inversely proportional to the peak value of the applied voltage, and the decreasing rates for higher water resistivities are much higher than those for lower water resistivities. The time to streamer corona initiation and the time to the second current peak become shorter as the voltage increases. Finally, the calculated resistances after streamer corona initiation are almost the same trace of measured resistances, but they are smaller than the measured values.