• Transactions on Electrical and Electronic Materials
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• 제16권3호
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• pp.146-150
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• 2015

Insulation breakdown voltage and insulation lifetime were investigated in straight lines or twisted pairs with polyesterimide-polyamideimide enameled round wires (EI/AIW ). The enamel thickness was 50 μm and the conducting copper radius was 0.50, 0.75, 1.09, and 1.50 mm, respectively. There were many air gaps in a twisted pair therefore, when voltage was applied to the twisted pair, enamel erosion took place in the air gap area because of partial discharge according to Paschen's law. Insulation breakdown voltage and insulation lifetime were highest in the sample of 0.75 mm conductor radius, which was higher than those values for 0.50 mm or 1.09 and 1.55 mm.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 전기설비
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• pp.23-24
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• 2006

Stator winding of hydro generator is gradually deteriorated by multi-stress and steady degradation of insulation results in insulation breakdown. The region where insulation breakdown occurs in stator winding is part where the multi-stress causes the defect of insulation material and electrical stress has been concentrated. Therefore, we judged locations of insulation breakdown to be varied according to various stress factors in service. In this paper, we drew the stator winding of hydro generators which has run for a long time and separated it into 3 parts(central part, end winding part, drawing part) according to the positions laid on the core. We performed electrical and thermal stress on these specimens for 1000 hrs under the same condition, measured the condition regularlyand analyzed the insulation status of each winding by performing partial discharge test. In addition, we analyzed the trend of partial discharge concerning specimens that caused the insulation breakdown during aging.

• 전기학회논문지
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• 제65권10호
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• pp.1712-1720
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• 2016

AC and DC insulation breakdown voltage was studied for magnet wire coated with double layers of high flexural PAI layer and high anti-corona PAI/nanosilica (15 wt%) layer. The specimens were prepared at various drying temperatures (T/D): $22^{\circ}C$, $240^{\circ}C$, and $260^{\circ}C$, respectively. The increase effects of nanosilica on AC and DC insulation breakdown voltage were not so significant compared to that of magnet wire coil coated with original PAI. And the AC and DC insulation breakdown voltage was improved by decreasing diameter of winding coil. As T/D temperature increased, AC and DC insulation breakdown voltage decreased.

• Journal of Power Electronics
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• 제3권3호
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• pp.159-166
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• 2003

The winding insulation of low-voltage induction motors in adjustable-speed drive system with voltage-fed Inverters is substantially stressed due to the uneven voltage distribution and excessive voltage stress (dv/dt), which result in the premature insulation breakdown 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, discharge inception voltage, AC current, and dissipation factor tests Also, insulation breakdown tests by high voltage pulses are performed, and the corresponding breakdown voltages obtained.

• 한국전기전자재료학회논문지
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• 제16권2호
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• pp.151-156
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• 2003

High temperature superconductor can only be applied against an engineering specofication that has to be determined for each particular application form the design requirements for economic viability and for operation margins in service. However, in order to realize the HTS transformer, it is necessary to establish the high voltage insulation technique in cryogenic temperature. Therefore, the composite insulation of double pancake coil type transformer are described and AC breakdown voltage characteristics of liquid nitrogen(LN$_2$) under HTS pancake coil electrode made by Bi-2223/Ag are studied. The Breakdown of LN$_2$ is dominated electrode shape and distance. The influence of pressure on breakdown voltage is discussed with th different electrode. For the electrical insulation design of turn-to-turn insulation for the HTS transformer, we tested breakdown strength of insulation sheet under varying pressure. And we investigated surface flashover properties of LN$_2$ and complex conition of cryogenic gaseous nitrogen(CGN$_2$) obove a LN$_2$ surface. The surface voltage of GFRP was measured as a function of thickness and electrode distance in LN$_2$ and complex condition of CGN$_2$ above a LN$_2$ surface. this research presented information of electrical insulation design for double pancake coil(DPC) type HTS transformer.

• 한국전기전자재료학회논문지
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• 제20권7호
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• pp.631-635
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• 2007

Diagnostic, surge and ac breakdown tests are widely used to evaluate the insulation condition of stator winding in traction motor. Diagnostic test included ac current, tan delta and maximum partial discharge. The result of diagnostic test indicates that five kinds of stator windings are good condition. Surge test was peformed to confirm the healthy of turn insulation in stator windings. This test is very easy to detect the turn insulation failure between normal and defect stator windings. After completing the diagnostic test, ac breakdown test has conducted gradually increasing ac voltage, until the stator winding punctured. No. 5 stator windings failed near rated voltage of 18.9 kV The breakdown voltage of No. 1 stator windings was 13.0 kV The ac breakdown voltage of normal winding is about 1.45 times higher than that of defect windings. The failure was located in a line-end coil at the exit from the core slot.

• 한국전기전자재료학회논문지
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• 제21권11호
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• pp.1024-1028
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• 2008

It is important that study on cryogenic electrical insulation design to develop the cold dielectric(CD) type HTS cable because the cable is operated under the high voltage environment in cryogenic temperature. This paper proposes two types of insulation design to carry out the maximum insulation design for 154 kV-class HT cable. The proposed insulation design method takes into consideration AC and lightning impulse withstand voltage so as to prevent AC breakdown for power frequency operating voltage during operating the cable and breakdown for lightning impulse voltage. The final insulation thickness is determined by selecting high value out of two insulation thickness calculated through the two insulation design methods. And we researched electrical insulation characteristics of HTS cable according to bending ratio and the number of bending.

• 한국전기전자재료학회논문지
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• 제18권10호
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• pp.950-955
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• 2005

For the insulation design of a high temperature superconducting(HTS) cable, three kinds of design method were proposed, which used AC and impulse withstand voltage and partial discharge inception strength. However, the designed insulation thickness by AC and impulse could not be applied to cable fabrication process due to much low electrical breakdown strength. The effect of the multi-layered insulation paper was not considered on the previous insulation design and the insulation thickness by partial discharge inception strength could be applied only. In this paper, the electrical breakdown characteristic, which considered the effect of multi-layered of LPP, was investigated to design the insulation thickness.

• 전기학회논문지
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• 제61권5호
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• pp.711-716
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• 2012

To assess the insulation deterioration of stator windings, diagnostic and AC breakdown tests were performed on the eleven high voltage (HV) motors rated at 6kV. After completing the diagnostic tests, the AC overvoltage test was performed by gradually increasing the voltage applied to the stator windings until electrical insulation failure occurred, to obtain the breakdown voltage. Stator winding of motors 1, 3, and 8 failed at above rated voltage at 14 kV, 13.8kV, and 16.4kV, respectively. The breakdown voltage of three motors was higher than expected for good quality windings in 6kV motors. Based on deterioration evaluation criteria, the stator winding insulation of eleven HV motors are confirmed to be in good condition. The turning point of the current, $P_{i2}$, in the AC current vs. voltage characteristics occurred between 5kV and 6kV, and the breakdown voltage was low between 13.8kV and 16.4kV. There was a strong correlation between the breakdown voltage and various electrical characteristics in diagnostic tests including Pi2.

• Journal of Electrical Engineering and Technology
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• 제13권4호
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• pp.1682-1691
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• 2018

Natural ester is a suitable substitute for mineral oil and has been widely used in AC transformer in many countries. In order to further application of natural ester in direct current (DC) equipment, it is needed to investigate its long term insulation property under DC condition. In this paper, a thermal ageing experiment was conducted for both mineral oil-paper and natural ester-paper insulation. The DC breakdown and space charge characteristics of insulation paper impregnated with natural ester and mineral oil was compared. Results show that the resistivity of the paper immersed in natural ester and mineral oil both increase as the ageing goes on. While insulation paper impregnated with natural ester has higher resistivity and DC breakdown voltage than the paper impregnated with mineral oil. The DC breakdown voltage for the oil impregnated insulation paper being DC pre-stressing is higher than that without pre-stressing. The average DC breakdown field strength difference between the test with pre-stressing and without pre-stressing clearly shows that there is an apparent enhancement effect for the homo-charge injection on the DC breakdown.