• 한국전기전자재료학회논문지
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• 제23권10호
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• pp.804-808
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• 2010

In this paper, we studied the dielectric breakdown voltage characteristics by the AC withstand voltage test on using green insulation dry air instead of $SF_6$ insulation gas used in the GIB (gas insulated bus) of 362 kV GIS (gas insulated switchgear). The AC withstand voltage test applied to the standard KEPCO's 362 kV GIB with dry air insulation, and the equivalence of dielectric breakdown voltage for dry air and $SF_6$ gas were examined, and the empirical formulas of dielectric breakdown voltage for dry air were calculated, and the criterion of AC withstand voltage test for dry air insulation was derived. Using the criterion, dry air can be used instead of $SF_6$ gas for 362 kV GIB in the factory acceptance test was confirmed.

• 전기학회논문지
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• 제58권4호
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• pp.788-794
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• 2009

To assess the condition of stator insulation, nondestructive tests were performed on twenty five coil groups and twenty six motors. The stator windings has nominal ratings of 6.6kV and are classified into five coil groups ;one group with healthy insulation and four groups with four different types of artificial defects. After completing nondestructive tests, the AC voltage applied to the stator windings was gradually increasing until insulation failure in order to obtain the breakdown voltage. No.1, No.2 and No.6 of 6.6kV motors failed near rated voltage of 14kV, 8.7kV and 14kV, respectively. The breakdown voltage of three motors was lower that expected for good quality coils(14.2kV) in 6.6kV motors. No.3 and No.6 of 4.16kV motors failed near rated voltage of 5.6kV and 4.2kV, respectively. Almost all of failures were located in a line-end coil at the exit from the core slot. The breakdown voltages and the types of defects showed strong relation to the stator insulation tests such as in the case of AC current, dissipation factor(tan${\delta}$) and partial discharge magnitude.

• Transactions on Electrical and Electronic Materials
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• 제17권5호
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• pp.297-301
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• 2016

The effects of ambient temperature and diameter on the insulation lifetime of winding coils prepared with polyamideimide (PAI), flexural PAI (nanosilica 5 wt%) and anti-corona PAI (nanosilica 15 wt%) wires were investigated. The winding coils were made of enameled wire with enamel thickness of 30~50 μm. The thickness and width of the rectangular copper wires were 0.77~0.83 mm and 1.17~1.23 mm, respectively. The insulation breakdown lifetime decreased with increasing ambient temperature regardless of wire type and winding coil diameter under an inverter surge of 1.5 kV/20 kHz. The insulation breakdown lifetimes of φ5 mm winding coils at 150, 200, and 250℃ were 11.38, 5.19, and 4.22 min respectively, and those of φ10 mm winding coils at 150, 200, and 250℃ were 11.32, 5.79, and 4.57min respectively. The winding coil diameter had little effect on the insulation lifetime.

• 한국산학기술학회논문지
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• 제19권1호
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• pp.69-74
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• 2018

산업사회의 발달과 더불어 신뢰성 높은 양질의 전기에너지와 운전 및 보수의 간편화, 계통 운용의 신뢰성, 안전성 확보가 요구되고 있다. 본 논문에서는 각종 전력설비에서 SF6을 대체하여 사용되고 있는 친환경절연제 $N_2-O_2$ 혼합가스 고체 절연물의 절연파괴특성과 고체절연재로 사용되고 있는 테프론의 연면절연특성을 압력에 따른 특성을 확인하였다. 대기와 비슷한 성분비 일 때 상대적으로 절연파괴특성이 테프론의 연면절연특성이 안정화되며, Paschen 법칙에 의해 평등전계에 가까운 전극중의 기체의 절연파괴전압은 압력에 비례하여 높아지고 있음을 실험을 통하여 확인하였다. 연면절연파괴전압은 압력에 따라 선형적으로 증가하였으며, 혼합가스의 $O_2$ 가스 혼합비에 따라 절연파괴전압의 차이가 발생하였다. 이는 $O_2$ 가스의 전기적 부성기체의 영향과 분자 간 충돌거리에 의해 연면절연파괴전압이 달라졌고, 본 연구에서 분자 간 충돌거리의 영향이 더 크게 작용하였다. 연면절연특성에 따른 테프론에 적용 가능한 절연파괴전압 관계식을 산출하였다. 이러한 결과는 전력설비의 절연설계 시 기초자료로 사용될 수 있을 것이라 생각된다.

• 한국초전도ㆍ저온공학회논문지
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• 제5권3호
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• pp.38-42
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• 2003

HTS transformer is promising one of HTS power applications to be commercialized in the near future. To realize the applications, insulation technology in the coolant, liquid nitrogen, should be established. So breakdown characteristics should be considered at insulation components; turn-to-turn, layer-to-layer, winding-to-winding, were investigated. Firstly breakdown strengths of Kapton films were compared with Kraft paper these are as turn insulator. And next the characteristics of surface flashover on FRP were measured and the influence on breakdown strength of bubble generated with joule heat was discussed with the shape of cooling channel between layers. Finally barrier effect at winding-to-winding was discussed.

• E2M - 전기 전자와 첨단 소재
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• 제11권10호
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• pp.32-39
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• 1998

Electrical breakdown strength of paper-oil and polypropylene/film-oil insulation samples was measured under dc, ac and pulsating voltages. The latter was obtained by superimposing ac upon dc volate and provides an attractive method for a simultaneous testing and assessment of the state of insulation of the various parts of HV apparatus in service. The measurements were carried out over a wide range of the pulsation ratio defined as p=Eac/Edc. The results obtained under pulsating voltages follow colsely an experssion which relates the breakdown strength to the sum of arc tangent and arc cotangent function of the parameter p. The study was carried out using dry paper as well as paper containing various degrees of moisture. The presence of moisture showed a pronounced effect upon the breakdown strength which varied with the pulsation parameter p.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 C
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• pp.1781-1783
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• 1996

Recently, the necessity of establishing the way to diagnose the aging of insulation materials and to predict of insulation breakdown become important. The purpose of our work are to investigate the treeing phenomena with a artificial needle shape void by the charge of partial discharge and acoustic emission pulse in each phase angle area at the same time. We have analyzed the ${\Phi}-Q-n$ pattern and the insulation diagnosis of the samples using statistic operators such as charge magnitude and A.E pulse factor, skweness, kurtosis, G,C. Therefore, the relation between the charge of partial discharge and A.E pulse will be helpful and efficient to predict the breakdown just before the breakdown occure.

• Transactions on Electrical and Electronic Materials
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• 제14권1호
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• pp.39-42
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• 2013

The effects of particle size on the mechanical and electrical properties of epoxy/spherical silica composites were studied. The silica particle sizes were varied from 5 to 30 ${\mu}m$ and the filler content was fixed to 60 wt%. Tensile and flexural tests were carried out and the interfacial morphology was observed by scanning electron microscopy (SEM). The electrical insulation breakdown strength was estimated using sphere-sphere electrodes with different insulation thicknesses of 1, 2 and 3 mm. The tensile strength and flexural strength increased with decreasing particle size, while electrical insulation breakdown strength increased with increasing particle size.

• 한국재료학회지
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• 제7권8호
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• pp.650-653
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• 1997

In large generators in power plants, stator winding insulations is exposed to a combination of thermal, electrical, mechanical, environmental stresses in service. These combined stresses cause insulation aging which leads to final insulation breakdown. In order to identify the breakdown mechanism, the stator winding insulation materials which are composed of mica-epoxy is analyzed by the component of materials with EDS, SEM techniques. We concluded that the potassium ions of mica are replaced by hydrogen ions at boundary area of mica-epoxy and/or mica-mica. It is proposed that through these phenomena, the conductive layers of potassium ions enable high voltage fields of multiple stresses to create voids and microcracks.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제52권8호
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• pp.354-358
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• 2003

In this paper, insulations characteristics by temperature changes(＋50～-50[$^{\circ}C$]) of $SF_{6}$ gas in the experimental chamber were studied. From this result, at the low temperature, the breakdown voltage was increased with a drop of temperature and an increase of inner pressure in GIS. In addition the ability of insulation of liquid $SF_{6}$ was higher than that of the highly pressurized $SF_{6}$ gas. That is, with progress of low temperature, the main reason of breakdown was not liquefaction of $SF_{6}$ but rapid decrease of inner pressure. This study will come in greatly handy for the insulation design of GIS in a hard cold region