• 한국전기전자재료학회논문지
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• 제29권12호
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• pp.829-834
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• 2016

Coil specimens were prepared by continuous coating on a copper wire with flexible PAI (polyamideimide) and PAI/nanosilica (5 wt%) varnish and thermally aged at 150, 200 and $250^{\circ}C$ for 5, 10 and 15 days, respectively. AC insulation breakdown voltage was investigated under inverter surge condition at 60 Hz and 1,000 Hz and insulation breakdown voltage decreased with increasing aging temperature and aging time at each 60 and 1,000 Hz.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1999년도 춘계학술대회 논문집
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• pp.529-531
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• 1999

In this Paper, the variable dielectric breakdown strengths of epoxy composites were investigated at belling absorption condition in order to observe the influences of moisture in out door use. Also. in order to improve withstand voltage properties at moisture absorbtion condition, IPN(interpenetrating polymer network) method was Introduced and the Influence was investigated. As Adding filler(SiO$_2$) classified by o(phr), 50(phr) and 100[phr] to two kinds of matrix resin, six kinds of specimens were manufactured. As a result, it was confirmed that dielectric breakdown strength wer degraded with boiling time and filer content increasing. But, it was confirmed that dielectric breakdown strength degrading rate were lowered by the Improvement of adhesion strength in IPN specimens.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1998년도 춘계학술대회 논문집
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• pp.163-166
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• 1998

In this paper, breakdown strength and dielectric characteristics were experimented in the structures of insulation/insulation/insulation and insulation/semiconductor/insulation by using of insulation material of polyethylene terephthalate film. The breakdown strength and the permitivity of each specimen were measured as a function of temperature and frequency respectively. The breakdown strength of PET/PET/PET did not changed greatly but that of PET/SEMl/PEr increased as a function of temperature. As the frequency inclosed, the permitivity of PET/PET/PET and PET/SEMI/PET decreased. The tan $\delta$ of PET/PET/PET showed lower than that of PET/SEMl/PET in low frequency but higher in high frequency .

• Journal of Electrical Engineering and Technology
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• 제5권2호
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• pp.264-269
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• 2010

This paper presents the analysis of the dielectric characteristics of a hot $SF_6$ gas in a gas circuit breaker. Hot gas flow is analyzed using the FVFLIC method considering the moving boundary, material properties of real $SF_6$ gas, and arc plasma. In the arc model, the re-absorption of the emitted radiation is approximated with the boundary source layer where the re-absorbed radiation energy is input as an energy source term in the energy conservation equation. The breakdown criterion of a hot gas is predicted using the critical electric field as a function of temperature and pressure. To validate the simulation method, breakdown voltage for a 145kV 40kA circuit breaker was measured for various conditions. Consistent results between the simulation and experiment were confirmed.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 추계학술대회 논문집 학회본부
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• pp.273-275
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• 1996

In order to investigate the electrical properties of naphthanic transformer oils for insulating and cooling, the characteristics for breakdown in temperature range of $20{\sim}100[^{\circ}C]$, that of AC breakdown in 1.0[mm] of gap length were made researches. As a result the characteristics for AC breakdown, it is confirm that the dielectric strength was increased to 6[ppm], 9[ppm] but decreased to 3[ppm].

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 추계학술대회 논문집
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• pp.65-68
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• 2000

Polyethylene, has long history and is widely used, was researched due to good electrical properties by many authors. But PE under stress has the critical defects of space charge accumulation and tree growth, so various methods such as catalyst, additives and blend to improve these problems have been execute, of which we selected blending method. As in our previous papers we investigated electrical conduction, dielectric and AC dielectric breakdown characteristics, we did DC dielectric breakdown characteristics in this paper. We selected pure LLDPE, pure EVA and LLDPE films mixed with EVA as specimens, which were mixed with the weight percentages of 50, 60, 70 and 80[wt%] to be thin film. DC applying voltage speed was 500[V/sec]. The relation between dielectric breakdown characteristics and the variations of super structure due to mixing was investigated, and especially trap level at amorphous region, threshold energy increment of conductive electron at free volume were considered.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2000년도 제18회 학술발표회 논문개요집
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• pp.187-187
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• 2000

Properties of electrical discharge in flames are investigated by making use of the ionization cross section of air. Fames have three distictive features. They are hot, emit light and are weakly ionized. We investigate influence of these three characteristics of flames on the electrical breakdown. It is found that the breakdown electric field in flames is inversely proportional to the flame temperature, thereby easily generating plasmas in flames. A swarm of low-energy electrons in flames would allow significant population of electronically excited states of flame molecules to be formed. Therefore, the analysis shows that the electronic excitation of flame molecules may also considerably reduce the breakdown field. Plasma electrons generate atomic oxygens by the electron attachment of oxygen molecules in high-pressure flames. These oxygen atoms are the most reactive radicals in flames for material oxidation. How are you and your family in this new year\ulcorner Professor Choi! I plan to go back Korea on February 6. All my family members are fine and have good time because I am here. Once I am in Korea, I will call you. I am always grateful for your helpful hand. Thank you so much.

• Transactions on Electrical and Electronic Materials
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• 제16권5호
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• pp.260-263
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• 2015

Epoxy/micro-sized alumina composite was prepared and the effects of alumina content on the electrical and mechanical properties were investigated in order to develop an insulation material for gas insulated switchgear (GIS). Nano-sized alumina (average particle size: 30 μm) was also incorporated into the epoxy/micro-sized alumina composite. An electrical insulation breakdown strength test was carried out in sphere-sphere electrodes and the data were estimated by Weibull statistical analysis. Tensile strength was measured at a crosshead speed of 10 mm/min using a universal testing machine. Alumina content was varied from 0 wt% to 70 wt%.). As micro-sized alumina content increased, insulation breakdown strength increased until 40 wt% alumina content and decreased after that content. The tensile strength of a neat epoxy system was 82.2 MPa and that value for 60 wt% alumina content was 91.8 MPa, which was 111.7% higher than inthe neat epoxy system. The insulation breakdown strength of micro-sized alumina (60 wt%)/nano-sized alumina (1 phr) glycerol diglycidyl ether (GDE) (1 phr) composite was 54.2 MPa, which was 116% higher than the strength of the system without nano-sized alumina.

• 한국전기전자재료학회논문지
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• 제31권7호
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• pp.496-501
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• 2018

In this study, we prepared 40, 45, 50, 55, 60, 65, and 70 wt% content composites filled in epoxy matrix for two micro silica and three micro alumina types for use as a GIS heavy electric machine. As a filler type of epoxy composite, micro silica composites showed excellent AC breakdown strength properties compared to micro alumina composites in the case of electrical properties of micro silica and alumina. The electrical breakdown properties of micro silica composites increased with increasing filler content, whereas those of micro alumina decreased with increasing filler content. In the case of mechanical properties, the micro silica composite showed improved tensile strength and flexural strength compared with the micro alumina composite. In addition, mechanical properties such as tensile strength and flexural strength of micro silica and alumina composites decreased with increasing filler content. This is probably because O-H groups are present on the surface of silica in the case of micro silica but are not present on the surface of alumina in the case of micro alumina.

• 한국세라믹학회지
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• 제51권3호
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• pp.177-183
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• 2014

Alumina-silica composite coating layers were prepared by electrophoretic deposition (EPD) of plate-shaped alumina particles dispersed in a sol-gel binder, which was prepared by hydrolysis and the condensation reaction of methyltrimethoxysilane in the presence of colloidal silica. The microstructure and the electrical and thermal properties of the coatings were compared according to the EPD process parameter: voltage, time and the content of the plate-shaped alumina particles. The electrical insulation property of the coatings was measured by a voltage test. The coatings were prepared by EPD of the sol-gel binder with 5-30 wt% plate alumina particles on parallel electrodes at a distance of 2 cm for 1-10 min under an applied voltage of 10-30 V. The coatings experienced increased breakdown voltage with increasing thickness. However, the higher the thickness was, the smaller the breakdown voltage strength was. A breakdown voltage as high as 4.6 kV was observed with a $400{\mu}m$ thickness, and a breakdown voltage strength as high as 27 kV/mm was achieved for the sample under a $100{\mu}m$ thickness.