• Journal of Electrical Engineering and Technology
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• v.12 no.3
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• pp.1245-1249
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• 2017

Recently, unusual transformer failures have been reported in 25kV power systems connected with a VCB and transformer. In this study, performance of the protection system, dielectric strength of the transformers, characteristics of switching surges and resonance phenomena were analysed and assessed. All investigations regarding the insulation breakdown of the transformers were carried out by simulations, laboratory tests, factory tests and on-site measurements in order to thoroughly investigate the root causes. Furthermore, experimental methods for investigating the resonance phenomenon were derived and tests were conducted applying the derived method to recreate the phenomenon in the transformer. It is found that resonance between the transformer and switching surge generated by closing a VCB can initiate the breakdown of internal windings of a transformer.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.542-543
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• 2005

In this paper, describes the fabrication and dielectric insulation characteristics experimental results of the model cable for the 22.9kV class HTS power cable. The model cable were tested with partial discharge(PD), AC and impulse withstand voltage in liquid nitrogen($LN_2$) and liquid nitrogen pressure. In these test results, PD inception stress and AC, impulse breakdown strength increase as the pressure of the liquid nitrogen increases.

• Journal of the Korean Vacuum Society
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• v.15 no.3
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• pp.266-272
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• 2006

Application of power higher than the optimum operation value to an external electrode fluorescent lamps(EEFL) leads to the formation of small holes, called pinholes, which subsequently leads to lamp failure. The pinholes come from the insulating breakdown of the capacitor which is the dielectric layer between an external electrode and glass tube. The power of insulation breakdown is proportional to the electric power applied to the lamp. When a lamp current is low in the glass tube of dielectric constant K, the dielectric field strength of pinholes is about 3K kV/mm. The field strength of insulation breakdown decreases as the lamp current increases.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.4
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• pp.381-387
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• 2007

The excellent dielectric properties of $SF_6$(sulfur hexafluoride) have lead to its wide range of application in the field of high voltage insulation. Because there has been some recent concern regarding the environmental impacts of $SF_6$ binary gas mixtures, with $SF_6$ as the main component, have been the subject of active research. Scientists have long been interested in the possible use of gaseous fluorocarbons, including $CF_4$ (Carton Tetrafluoride), in high voltage applications due to their inert character and high dielectric strength. This paper presents experimental results concerning the AC breakdown characteristics lot various mixtures of $SF_6/CF_4$ in a test chamber and 25.8 kV GIS (Gas Insulation Switchgear) at practical pressures (0.1-04 MPa) and gap lengths (0.5 mm, 1 mm) in a test chamber. In the result, it was observed that an increase in the dielectric strength is attained through the addition of $SF_6$ to $CF_4$. It is possible to make an environment friendly gas insulation material while maintaining the dielectric strength by combing $SF_6$ and $CF_4$ which generates a lower level of the "global warming" effect.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.544-547
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• 1999

To develop the better insulants. the zeolite particle, which is aluminosilicate mineral, was filled In the DGEBA/MDA/SN epoxy resin system. Dynamic DSC curves of cured specimens with various contents of zeolite were observed and the glass transition temperature(T$_{g}$) was obtained. According to this result, we could carry out the experiment concerned with the dielectric breakdown strength around T$_{g}$ and find the limit temperature for the application of the DDEBA/MDA/SN system filled with natural zeolite. T$_{g}$ increased with the content of zeolite. As the temperature increased, the dielectric breakdown strength decreased rapidly, in the region of T$_{g}$. At the high temperature, the deterioration by electrical stress was activated. The diameter of puncture at the high temperature was larger 7han that at the room temperature.erature.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05a
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• pp.61-64
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• 2003

The degradation of the dielectric properties of insulating papers that were used under loaded conditions at cryogenic temperature was paid attention. Electrical and tensile stress properties of dielectric paper at cryogenic temperature have been investigated to optimum insulating design of high-Tc superconducting(HTS) cable. Tensile strength of PPLP in liquid nitrogen was high more than that of air, but tensile strain could know that decrease sharply. According as tensile strength increases, the breakdown stress of PPLP in liquid nitrogen was decreased.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2006.05a
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• pp.487-492
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• 2006

Inverter driven induction motors with high speed switching and advanced PWM techniques are widely used for variable speed applications. Recently, the insulation failures of stator winding have attracted much concern due to high dv/dt of IGBT PWM inverter output. In this paper, the detailed insulation test results of 26 low-voltage induction motors are presented. Six different types of insulation techniques are applied to 26 motors. The insulation characteristics are analyzed with partial discharge, inception voltage, AC current, and dissipation factor tests. Also, breakdown tests by high voltage pulses are performed. From the above test data the effects due to different wires and insulation techniques on the insulation characteristics of low-voltage induction motors are compared and analyzed. The insulation technique to enhance the insulation strength is suggested from the test results.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.99-99
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• 2010

Polymer nanocomposite has been attracting much attention as a new insulation material, since homogeneous dispersion of nm-sized inorganic fillers can improve various properties significantly. In this paper, various kinds of epoxy based nanocomposites were made and AC breakdown strength of Nano-TiO2 and micro-silica filler mixture of epoxy based composites were studied by sphere to sphere electrode. Moreover, nano- and micro-filler combinations were adopted as an approach toward practical application of nanocomposite insulation materials. Nano-TiO2 particle size is about 10nm and composites ratio was resin (100) : hardener (82) : accelerator (1.5). AC breakdown test was performed at room temperature (25 [$^{\circ}C$], 80 [$^{\circ}C$] and 100 [$^{\circ}C$] in the vicinity of Tg (90[$^{\circ}C$]). And thermal conductivity were measured by ASTM-D5470.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1608-1610
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• 2000

In this work, the effect of annealing on physical and electrical properties of XLPE cable insulation was investigated. One sample was non-annealed and the other two samples were treated under air circulated oven at 80$^{\circ}C$ for five and ten days. In the DSC patterns of annealed specimen, new peaks appeared at near 80$^{\circ}C$ as a proof of thermal history. The degree of crystallinity increased by annealing effect. In the FT-IR spectrums, the change of absorbances to acetophenone and cumyl alcohol were observated according to the radial direction of cable insulation. They slowly diffused into both semi-conductive layer of the cable in proportion to annealing time and lastly led to near equilibrium state through cable insulation. The AC breakdown strength did not increased but the values were stabilized by effects of crystallinity and diffusion of by-products.

• Proceedings of the KIEE Conference
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• 1999.07e
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• pp.2120-2122
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• 1999

$SF_6$ gas has been widely used the gas insulated transmission line, gas insulated transformer and gas insulated substation and Polyester film used as the turn insulation with other material. $SF_6$ gas has been actively studied in domestic and foreign countries. In general, when dielectric surface electric field exceed any electric field strength on air, corona discharge is occurred from the dielectric surface. This paper presents the insulation strength of turn insulation of $SF_6$-PET film studied under application of AC voltage, constitute of the plane to plane with PET Film. The results obtained in experimental are summarized that Partial Discharge Initial Voltage(PDIV) of turn insulation depend on gas pressure, but Breakdown Voltage(BDV) did not depend on gas pressure.