• Journal of the Korean institute of surface engineering
• /
• v.28 no.4
• /
• pp.236-242
• /
• 1995

This paper describes a study of electrical tree growth in DGEBA/MDA/SN system subjected to ac high electric field. The dielectric breakdown process, which consists of tree initiation, tree propagation and the complete puncture of the system was investigated. Dielectric breakdown always initiated from the needle tip where the electric field reinforcement is the highest. Higher temperature and voltage accelerated the tree growth and reduced the time to breakdown.

• Journal of Electrical Engineering and Technology
• /
• v.10 no.2
• /
• pp.647-652
• /
• 2015

A fully coupled finite element analysis (FEA) technique was developed for analyzing the discharge phenomena and dielectric liquid flow while considering surface charge density effects in dielectric flow guidance. In addition, the simulated speed of surface charge propagation was compared and verified with the experimental results shown in the literature. Recently, electrohydrodynamics (EHD) techniques have been widely applied to enhance the cooling performance of electromagnetic systems by utilizing gaseous or liquid media. The main advantage of EHD techniques is the non-contact and low-noise nature of smart control using an electric field. In some cases, flow can be achieved using only a main electric field source. The driving sources in EHD flow are ionization in the breakdown region and ionic dissociation in the sub-breakdown region. Dielectric guidance can be used to enhance the speed of discharge propagation and fluidic flow along the direction of the electric field. To analyze this EHD phenomenon, in this study, the fully coupled FEA was composed of Poisson's equation for an electric field, charge continuity equations in the form of the Nernst-Planck equation for ions, and the Navier-Stokes equation for an incompressible fluidic flow. To develop a generalized numerical technique for various EHD phenomena that considers fluidic flow effects including dielectric flow guidance, we examined the surface charge accumulation on a dielectric surface and ionization, dissociation, and recombination effects.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.16 no.1
• /
• pp.35-43
• /
• 2002

In the last decade, considerable efforts have been made to make a new class of solid state high power, high speed electronic device, namely, the Photo-Conductive Power Switch(PCPS), and to characterize the high-field performance of PCPS under high power, high voltage conditions. But the problem of surface flashover phenomena persist, preventing the realization of reliable and efficient high-speed, high voltage switching devices. It is essential to have a clear understanding on the physical processes behind the surface flashover problem to develop new technologies and device architectures so as to fabricate PCPS that are capable of high-field high-voltage. Also, it is imperative to identify new materials that could satisfy the requirements for high-field, high-power devices. Since surface flashover, surface breakdown phenomena is observed for all the devices that foiled at the applied field much lower than semiconductor bulk breakdown field, surface passivation is considered one of the important practical methods to improve the high field performance of the devices. Therefore, this paper was studied the main properties and mechanism of the semiconductor surface flashover before and after passivation under high electric-field.

• 전기의세계
• /
• v.24 no.5
• /
• pp.82-90
• /
• 1975

This study investigated the deterioration phenomena of the Polyethylene surface contaminated with organic(Saccharose) or inorganic(NaCl) matters through electrical and optical experiments. And also these experimental results relatively well coincided with which was treated by theoretical process. On the electrical experiment, relation between electric field intensity in corona discharge and time reached to the breakdown, and relation between total amount of charges discharged and increment of applied voltage were investigated. On the optical experiment, discharge time dependence of surface deterioration rate and process of surface deterioration in the X-ray diffraction pattern were investigated. It was concluded that chemical effects by the corona discharge deteriorated insulation characteristics of Polyethylene surface.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.11 no.3
• /
• pp.22-26
• /
• 1974

The effects of anisotropic mechanical stress applied normal to the surface of p-n junctions have been investigated. As the stress increased, the breakdown voltage was decreased and the breakdown mode became softer. Within a certain limitation in the applied stress, the above phenomena werw reversibbe, though relaxation and hysteresis phenomena were observed. The time constant of relaxation depended upon the shape of the stressing tip, but for the given tip and device a unique time constant was obtained. The stress.dependence of breakdown voltage showed a good linearity up to about 3.0${\times}10^4$ kgw/$\textrm{cm}^2$, when the flat tip of radius 15$\mu$ was used, and the temperatere-dependence of breakdown voltage under the stress also showed a good linearity in the temperature range of 100 to $300^{\circ}K$.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.27 no.7
• /
• pp.1033-1041
• /
• 1990

In this paper, under pinch-off conditions, the gate-drain breakdown voltage characteristics of GaAs Power MESFET's as a function of device parameters such as channel thickness, doping concentration, gate length etc. are analyzed. Using the Green's function, the gate ionic charge induced by the depleted channel ionic charge is calculated. The impact ionization integral by avalanche multiplication between gate and drain is used to investigate breakdown phenomena. Especially, the localized excess surface charge effect as well as the uniform surface charge effect on breakdown voltage is considered.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
• /
• 2005.05a
• /
• pp.279-282
• /
• 2005

Morden electronic equipments are becoming very important in information oriented society, but they are vulnerable to lightning surges. Soil resistivity in the vicinity of grounding electrodes my be affected by the current flowing from the grounding electrodes into the surrounding soil. Electrical conduction in soils depends on the grain size, compactness, and variability of the grain sizes. When a high current is injected into the soil, and the breakdown phenomenon occur. In the present work, Electrical behaviors related to discharge in soils were investigated. The breakdown voltages in soil were lower than that sparkover voltage in air. The breakdown voltage in the gravel layer is relatively low, and the breakdown was caused by the flashover through the surface of gravels

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2000.07a
• /
• pp.82-85
• /
• 2000

The less sensitive structure to the surface effect has been presented utiliting an undoped GaAs layer on the n-GaAs channel. The undoped layer has been found to be effective to supress the frequency dispersion phenomena caused by a surface trapping effect and to raise the MESFET's performance. The gate structure, with an undoped layer underneath the gate metal has been found to be effective to improve the breakdown voltage. GaAs MESFETS with different physical structures are fabricated and DC characteristics are measued. GaAs MESFET's are fabricated on epi-wafers which have an undoped GaAs layer in between n+ and n GaAs layers grown by MBE.

• Journal of Electrical Engineering and information Science
• /
• v.2 no.3
• /
• pp.71-76
• /
• 1997

A lot of experiments and analyses have been done to determine the aging mechanism of mica-epoxy composite material used for large generator stator windings in order to estimate remaining life of the generator for last decades. After degrading artificially the mica-epoxy composite material, the surface analysis is performed to analyze breakdown mechanism of insulation in air and hydrogen atmosphere; i) In the case of air atmosphere, it is observed that an aging propagation from conductor to core by partial discharge effect and the formation of cracks between layers is widely carbonized surface. ii) In case of hydrogen atmosphere, the partial discharge effect is reduced by the hydrogen pressure (4kg/$\textrm{cm}^2$). Potassium ions forming a sheet of mica is replaced by hydrogen ions, which can lead to microcracks. It is confirmed that the sizes of crack by SEM analysis are 10∼20[$\mu\textrm{m}$] in length under air, and 1∼5[$\mu\textrm{m}$] in diameter, 10∼50[$\mu\textrm{m}$] in length under hydrogen atmosphere respectively. The breakdown mechanism of sttor winding insulation materials which are composed of mica-epoxy is analyzed by the component of materials with EDS, SEM techniques. We concluded that the postassium ions of mica components are replaced by H\ulcorner, H$_3$O\ulcorner at boundary area of mica-epoxy and/or mica-mica. It is proposed that through these phenomena, the conductive layers of potassium enable creation of voids and cracks due to thermal, mechanical, electrical and environmental stresses.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.56 no.2
• /
• pp.343-348
• /
• 2007

The physical properties of DMPC monolayer were made for dielectric relaxation phenomena by the detection of the surface pressures and displacements current. Lipid thin films were deposited by accumulation and the current was measured after the electric bias across the manufactured MIM device. It is found that the phospolipid monolayer of dielectric relaxation takes a little time and depend on the molecular area. When electric bias is applied across the manufactured MIM device by the deposition condition of phospolipid mono-layer, it wasn't breakdown when the higher electric field to impress by increase of deposition layers.