• Proceedings of the KSR Conference
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• 2003.10c
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• pp.606-610
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• 2003

The 200 class insulation system which adopted to traction motor have excellent dielectric strength but weaken to thermal stress therefore deterioration phenomena analysis according to thermal stress is necessary. Accelerated thermal aging tests have been used to determine thermal reliability of stator coils used as traction motor in electric multiple unit. The conventional aging test is carried on according to IEC 60034-18-31 and IEEE Std. 275-1992. Variation in insulation resistance, P.I, capacitance, dielectric loss($tan{\delta}$) and partial discharge are measured during the aging cycle. Sample coils for traction motor were tested by accelerated aging test which composed of heat, vibration and moisture. Reliability and expected life were evaluated on the insulation system for traction motor.

• Proceedings of the KIEE Conference
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• 2004.11a
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• pp.3-8
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• 2004

The Pulse Width Modulation (PWM) Inverter plays an important role in express locomotive. Especially after traction motors are fed by fast switching inverters, the interturn insulation is destroyed more heavily. However, a new type of polyimide corona resistant film is developed and used in insulation of traction motors. In order to investigate the service life of this kind of traction motor, the mechanism and characteristics of dielectric breakdown of polyimide corona resistant are studied in the paper. Experiments have been carried out on specimen according to the condition of traction motor. The breakdown point of tested sample film is analyzed through energy spectrum analysis and electron microscopic photograph. At last, it is presented that the characteristics and mechanism of breakdown of polyimide corona resistance film.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.921-922
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• 2007

In recent years, environmental concerns have been raised on the use of poorly biodegradable fluids in electrical apparatus in regions where spills from leaks and equipment failure could contaminate the surroundings. For development of the environmental-friendly pole transformer using vegetable oil, we discussed the insulation construction of the transformer and the dielectric characteristics of the Nomex insulation paper in vegetable oil. Based on the experimental data, the insulation of the transformer is designed.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.8
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• pp.32-39
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• 2015

This paper presents the surface flashover mechanism of a laminated solid dielectric and describes the surface flashover characteristics with the inherent capacitance of the laminated solid dielectric in a $N_2/O_2$ mixture gas (8:2) under an quasi uniform field. It was found that the electron emission at a cathode and the high-local electric field region around an anode were important factors to reasonably describe the surface flashover mechanism. The surface flashover voltage by the mechanism decreased with the inherent capacitance increase of the laminated solid dielectric. In addition to the surface flashover mechanism and its characteristics, the surface flashover voltage equations as a function of the inherent capacitance were derived by considering a gas pressure used in future eco-friendly GIS and the factors influencing the surface flashover.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07a
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• pp.78-81
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• 2004

In this paper, the effect of adhesion properties of semiconductive-insulating interface layer of silicone rubber on electrical properties was investigated. Surface structure and adhesion of semiconductive silicon rubber by surface asperity was obtained from SEM and T-peel test. In addition, ac breakdown test was carried out for elucidating the change of electrical property by roughness treatment. From the results, Adhesive strength of semiconductive-insulation interface was increased with surface asperity. Dielectric breakdown strength by surface asperity decreased than initial Specimen, but increased from Sand Paper #1200. According to the adhesional strength data unevenness and void formed on the silicone rubber interface expand the surface area and result in improvement of adhesion. Before treatment Sand Paper #1200, dielectric breakdown strength was decreased by unevenness and void which are causing to have electric field mitigation small. After the treatment, the effect of adhesion increased dielectric breakdown strength. It is found that ac dielectric breakdown strength was increased with improving the adhesion between the semiconductive and insulating interface.

• Progress in Superconductivity and Cryogenics
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• v.8 no.1
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• pp.45-48
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• 2006

In the response to the demand for electrical energy , much effort was given to develop and commercialize high temperature superconducting (HTS) power equipments has been made around the world. Especially, HTS transformer is one of the most promising devices . but the cryogenic insulation technology should be established during development Hence many types of dielectric tests should be carried out to understand the dielectric phenomena at cryogenic temperature and to gather various dielectric data. Among the many types dielectric tests . the characteristic of barrier effect were conducted using simulated electrode after analysing the insulating configuration of HTS transformer main winding. The influence of a barrier on the dielectric strength was measured according to the position of the harriet the number of the barrier and thickness or the barrier. It was shown that the effectiveness . namely the ratio of the breakdown voltage in presence of barrier to the voltage without barrier, is highest when the barrier is placed at the needle electrode side. On the contrary, in the case of having the barrier between the electrodes, the harrier was placed between the electrodes the characteristic was even improved slightly.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.8
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• pp.1560-1565
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• 2011

The environmental pollution caused by green-house gases such as $CO_2$ and $SF_6$ has been becoming the main issue of industrial society. Many developed countries are making efforts to minimize the amount of $CO_2$ emission come from the operation of high voltage electrical apparatuses. As a part of these efforts, 180 countries signed the Kyoto Protocol in 1997 to cut back on their green-house gas emissions. Nowadays, the study on the development of dry air insulated switchgear (DAIS) which is known as an eco-friendly electrical apparatus is in progress. A DAIS is advantageous for minimizing the effect of impurities and enhancing the dielectric characteristics over an air insulated switchgear (AIS) by applying constant pressure to an enclosed cubicle. Therefore, a study on the electrical insulation performance of dry air as a gaseous insulation medium is conducted in this paper to substitute a gas insulated switchgear (GIS) for DAIS. As results, it is verified that the AC dielectric characteristics of dry air are similar to those of air and the lightning impulse dielectric characteristics of dry air are superior to those of air at 1bar pressure condition. However, dry air is of inferior dielectric characteristics to $SF_6$ at 4bar pressure condition. Finally, it is suggested that the internal pressure of DAIS should be over 4bar pressure to develop a high voltage switchgear which has similar electrical performance to a conventional GIS. Also, the empirical formulae on calculating the maximum electric field intensity at sparkover of dry air are deduced by experiments according to pressures. It is expected that these results are helpful to design and develop a high voltage electrical apparatus.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.55 no.8
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• pp.411-416
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• 2006

A new method on the evaluation of insulation oil was proposed. Terahertz time-domain spectroscopy (THz-TDS) was applied to investigate the properties of the insulating oil. For the diagnostics of oil degradation, three kinds of oils have been analyzed by THz-TDS. The degraded oil showed different optical and electrical constants compared with a new one. Generally, the power absorption coefficient, the refractive index, the dielectric constant and loss $tan{\delta}$ of the oil increase as the aging of insulating oil proceed. And the characteristics of two kind of insulation oil, 1-4 and 7-4, was compared in terahertz spectral region. Difference in refractive index and complex dielectric constant has been observed between the samples. The results of this study suggest that THz-TDS is a promising new means for evaluating degradation and identification of insulating oil.

• Proceedings of the KIEE Conference
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• 1998.11c
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• pp.938-940
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• 1998

In order to improve insulating character and ability of insulating system of power apparatus, the interfacial and complex structure is widely used. However, the interface or complex structure of insulation materials is reported as a weak point which causes breakdown. As the interface of insulation system degrades its electrical property and eventually causes a failure, the datailed phenomenon analysis is reported. The object of this paper is to evaluate dielectric property of PET film with the interface. The $tan{\delta}$ increased with the existence of semiconducting layer and showed prominent decrease as a function of temperature. Also, the $tan{\delta}$ showed prominent increase as a function of frequency. The dielectric properties of interfacial were affected by the interface characteristics.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.256-257
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• 2008

Recently, with the increase of demand of electricity, electric cable or electric transfer machine are rapidly developed and meet the demand with the extra high voltage and massive capacity, the dangers of electrical accident of insulator are increasing by the electric stress, insulation degradation and insulation breakdown in insulator. In this paper, it is investigated that the temperature dependance of dielectric strength in nano-composites. We obtained that breakdown voltage of 0.4 [wt%] specimens is higher than the other $SiO_2$ content.