• Journal of Electrical Engineering and Technology
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• v.6 no.3
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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 $\phi_b$.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.8
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• pp.1398-1406
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• 2008

This paper describes the electrical breakdown characteristics of broken toughened glass stem insulators by comparing with those of sound ones. The broken toughened glass stem insulators were taken from the electric railway field. According to the international standards, the sound and broken toughened glass stem insulators were tested in electrical strength. In the test, the power frequency voltage and the impulse voltage with a standard waveform were applied to the insulators. The power frequency voltage tests were carried out under both dry and wet condition and the impulse voltage tests under only dry condition. The acquired results were compared one another and discussed in electrical breakdown characteristic by analyzing the flashover progress pictures. As a result, the electrical strength of the broken toughened glass insulators was acquired and the processes of the surface breakdown on the toughened glass insulators were confirmed.

• 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.

• Electrical & Electronic Materials
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• v.7 no.5
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• pp.376-382
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• 1994

In this study we developed a program(DEVSIM) to simulate the two dimensional distribution of the electrostatic potential and the electric field of the arbitrary structure consisting of GaAs/AlGaAs semiconductor and metal as well as dielectric. By the comparision of the electric field distribution of GaAs MESFETs with the various recess gates we proposed a suitable device structure to improve the breakdown characteristics of MESFET. According to the results of simulation the breakdown characteristics were improved as the thickness of the active epitaxial layer was decreased. And the planar structure, which had the highly doped layer under the drain for the ohmic contact, was the worst because the highly doped layer prevented the space charge layer below the gate from extending to the drain, which produced the narrow spaced distribution of the electrostatic potential contours resulting in the high electric field near the drain end. Instead of the planar structure with the highly doped drain the recess gate structure having the highly doped epitaxial drain layer show the better breakdown characteristics by allowing the extention of the space charge layer to the drain. Especially, the structure in which the part of the drain epitaxial layer near the gate show the more improvement of the breakdown characteristics.

• Proceedings of the KIEE Conference
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• 1999.11d
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• pp.1099-1101
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• 1999

PJB(Prefabricated Joint Box) is consisted of three major components ; an epoxy unit, a stress relief cone and a spring unit. The insulation structure of PJB is maintained by the interfacial pressure, and the dielectric performance at the interface depends on the interfacial pressure which is regarded as the most important factor for preventing breakdown failure. This experiment was performed to investigate breakdown voltage characteristic and partial discharge patterns under the controlled pressure conditions at the simulated interface. Finally, this paper presents the optimal pressure conditions at the interface by analyasing the PD patterns.

• Journal of Electrical Engineering and Technology
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• v.12 no.2
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• pp.858-864
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• 2017

This study aims to restrain free conducting wire-type particles which are commonly and dangerously existing within DC gas-insulated transmission lines. A realistic platform of a coaxial cylindrical electrode was established by using a high-speed camera and a partial discharge (PD) monitor to observe the motion, PD, and breakdown of these particles. The probabilities of standing or bouncing, which can be affected by the length of the particles, were also quantitatively examined. The corona images of the particles were recorded, and particle-triggered PD signals were monitored and extracted. Breakdown images were also obtained. The air-gap breakdown with the particles was subjected to mechanism analysis on the basis of stream theory. Results reveal that the lifting voltage of the wire particles is almost irrelevant to their length but is proportional to the square root of their radius. Short particles correspond to high bouncing probability. The intensity and frequency of PD and the micro-discharge gap increase as the length of the particles increases. The breakdown voltage decreases as the length of the particles decreases.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.693-696
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• 2004

For InGaP/GaAs HBT applications, we have developed characterized MIM capacitors with thin $1000{\AA}$ PECVD silicon nitride which were deposited with $SiH_4/NH_3$ gas mixing rate, working pressure, and RF power of PECVD at $300^{\circ}C$ and had the capacitance density of 600 pF/$mm^2$ with the breakdown electric fields of 3073 MV/cm. Three PECVD process parameters were designed to lower the refractive index and then lower the deposition rate of silicon nitride films for the high breakdown electric field. At the PECVD process condition of gas mixing rate (0.92), working pressure (1.3 Torr), RF power (53 W), the AFM Rms value of about $1000{\AA}$ silicon nitride on the bottom metal was the lowest of 0.662 nmand breakdown electric fields were the highest of about 73 MV/cm.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.509-510
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• 2007

The Breakdown properties of epoxy composites are used for transformers and sensor, which has been studied. As a result, From the measurements of breakdown voltage, the more hardener is increased the stronger breakdown strength at low temperature because the ester of hardener is increased. Breakdown strength at the high temperature is decreased because the temperature at $110^{\circ}C$ is near at $T_g$. When the filler is added, between epoxy and silica is formed interface. Therefore the charge is accumulated in it, and the electric field is concentrated, and breakdown strength is decreased than non-filled specimens. In the case of specimens, the treated with silane, the breakdown strength becomes much higher since this is suggested that silane coupling agent has been improved chemical bonding in the interfaces and has been relaxed the electric filed concentration.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.98-98
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• 2010

A epoxy/multilayered silicate nanocomposite was prepared by a new AC electric application method and micro silica particle was poured into the nanocomposite in order to prepare epoxy/micro-and-nano- mixed composites (EMNC). Electric insulation breakdown strength was measured in a sphere-sphere electrode system designed for the prevention of edge breakdown and the data were estimated by Weibull plot. As the exfoliated silicate nano-plates were homogeniously dispersed in the micro silica particles, the insulation property was higher.

• 전기의세계
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• v.16 no.4
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• pp.11-16
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• 1967

A physical analysis is applied to the measured phenomena of aromatic organic compounds under the uniform electric field of 0.1MV/cm through 1.5MV/cm, when they are irradiated or non-irradiated respectively. Upon the observations about irradiation effects, space charge effects and their temperature dependance, the conditions of lattice defects act conspicuously on electric conductrivity, photo conductivity and dielectric breakdown. Although the qualitative agreement with Frohlich's high energy criterion theory for the above mechanisms is poor, it is concluded that the phenomena of aromatic compounds may possibly be due to the effect of lattice defects or impurity centers generated by .gamma.-ray irradiations.