• Title, Summary, Keyword: Mica/epoxy

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A Study on Mechanical, Electrical Properties of Epoxy/MICA Composites with MICA Filled Contents (Epoxy/MICA 복합체의 MICA 충진함량 변화에 대한 기계적, 전기적 특성연구)

  • Park, Jae-Jun
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.62 no.2
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    • pp.219-227
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    • 2013
  • This paper reported a study on the thermal, mechanical and electrical insulation properties of epoxy/mica composites. To investigate the effect of mica content, glass transition temperature, mechanical properties such as tensile and flexural strength, and insulation breakdown properties for epoxy composites with various contents of mica. The effect of insulation thickness on insulation breakdown property was also studied. It was observed that tensile and flexural strength decreased with increasing mica content, while elastic modulus increased as the mica content increased. AC insulation breakdown strength for all epoxy/mica composites was higher than that of neat epoxy and that of the system with 20 wt% mica was 14.4% improved. As was expected, insulation breakdown strength at $30^{\circ}C$ was far higher than that at $130^{\circ}C$, and it was also found that insulation breakdown strength was inversely proportion to insulation thickness.

AC Electrical Breakdown Characteristics of an Epoxy/Mica Composite

  • Park, Jae-Jun
    • Transactions on Electrical and Electronic Materials
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    • v.13 no.4
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    • pp.200-203
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    • 2012
  • Epoxy/mica composite was synthesized, in order to use it as an impregnation resin in a vacuum pressure impregnation (VPI) process, for manufacturing a high voltage rotary machine. The average particle size of the mica was 5~7 ${\mu}m$ and its content was 0, 20, 30 and 40 wt%. A plasticizer or a low molecular aliphatic epoxy was also used, to decrease the viscosity of the composite. The AC electrical breakdown strength was estimated in sphere-to-sphere electrodes, and the electrical breakdown data were estimated by Weibull statistical analysis. The electrical breakdown strength became higher with the addition of mica; and that of the system with 20 wt% mica was highest. The electrical breakdown strength of the system with an aliphatic epoxy was higher than that of the system with a, plasticizer.

A Study on Thermal, Mechanical and Electrical Properties as Silane Treated Epoxy/MICA Composites (실란처리된 Epoxy/MICA 콤포지트의 열적, 기계적 전기적 특성연구)

  • Park, Jae-Jun
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.62 no.2
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    • pp.213-218
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    • 2013
  • In this study, epoxy/mica composite was prepared by mixing with mechanical stirrer together with homogenizer, and the effect of amino-type silane coupling agent was also studied. To reduce the viscosity without any decrement of other properties, 1,4-Butanediol diglycidyl ether (1,4-BDGE) as an aliphatic epoxy reactive diluent was introduced to the epoxy/mica composite in order to use as vanish for high voltage motor and generator stator winding. It was confirmed by scanning electron microscopy (SEM) observation that interfacial characteristics between organic epoxy and inorganic mica was modified by coupling agent treatment so that glass transition temperature increased, and tensile strength and electrical breakdown strength increased. The properties were estimated by Weibull statistical analysis and the ac electrical breakdown strength was 20.2% modified by treating silane coupling agent.

A Study on the Insulation Breakdown of Mica-Epoxy Composites (Mica-Epoxy 복합재료의 절연파괴에 관한 연구)

  • Kim, Hui-Gon;Kim, Hui-Su
    • Korean Journal of Materials Research
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    • v.7 no.8
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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.

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The Aging Characrteristic Analysis of Mica-Epoxy Insulation Materials (마이카-에폭시 절연재료의 열화특성분석)

  • Yoo, Yeong-Sik;Kim, Hee-Gon;Song, Woo-Chang;Lee, Jae-Hyung;Park, Yong-Kwan
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.11 no.2
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    • pp.82-89
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    • 1998
  • The experimental results using the X -ray technique, the position and structure of mica crystal are not observed the phase change of aging and sound specimen respectively. However, We could observe the intensity difference of crystal element in both atmospheres. The analysis of mica-epoxy materials by optical microscope are shown that the each surface of sound and aging specimens are different in both atmospheres Also, the experimental results have shown that the potassium ions of mica cristal are substituted by hydrogen ions at boundary area of mica-epoxy and/or mica-mica. On components made of mica, a potassium ion of big atomic radius, is replaced by hydrogen ion of small atomic radius. The voids are created by the difference of radius progressed by combined stresses. Through these phenomena, it has been proposed that the conductive layers made of potassium enable the voids to form and the cracks to create by high electric field.

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A Study on the Breakdown Mechanism of Rotating Machine Insulation

  • Kim, Hee-Gon;Kim, Hee-Soo;Park, Yong-Kwan
    • Journal of Electrical Engineering and information Science
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    • v.2 no.3
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    • pp.71-76
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    • 1997
  • A lot of experiments and analyses have been done to determine the aging mechanism of mica-epoxy composite material used for large generator stator windings in order to estimate remaining life of the generator for last decades. After degrading artificially the mica-epoxy composite material, the surface analysis is performed to analyze breakdown mechanism of insulation in air and hydrogen atmosphere; i) In the case of air atmosphere, it is observed that an aging propagation from conductor to core by partial discharge effect and the formation of cracks between layers is widely carbonized surface. ii) In case of hydrogen atmosphere, the partial discharge effect is reduced by the hydrogen pressure (4kg/$\textrm{cm}^2$). Potassium ions forming a sheet of mica is replaced by hydrogen ions, which can lead to microcracks. It is confirmed that the sizes of crack by SEM analysis are 10∼20[$\mu\textrm{m}$] in length under air, and 1∼5[$\mu\textrm{m}$] in diameter, 10∼50[$\mu\textrm{m}$] in length under hydrogen atmosphere respectively. The breakdown mechanism of sttor winding insulation materials which are composed of mica-epoxy is analyzed by the component of materials with EDS, SEM techniques. We concluded that the postassium ions of mica components are replaced by H\ulcorner, H$_3$O\ulcorner at boundary area of mica-epoxy and/or mica-mica. It is proposed that through these phenomena, the conductive layers of potassium enable creation of voids and cracks due to thermal, mechanical, electrical and environmental stresses.

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A Study of development on Mica/Epoxy Composite (2) (마이카/ 에폭시 복합재료의 개발에 관한 연구(2))

  • Park, Chung-Hoo;Jeung, Eun-Shik;Kim, Ki-Beom
    • Proceedings of the KIEE Conference
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    • pp.216-219
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    • 1987
  • Dielectric and Mechanical Properties of Mica flake/ Epoxy Composite are investigated. The Mica content is about 50 wt % and its thickness is about $240{\mu}m$. The finished Mica flake/Epoxy Composite contains about 0.1-1.0 wt % of aminosilane coupling agent. Ruby Mica filler and high temperature curing Epoxy resin are used. From the viewpoint of dielectric and mechanical properities. the optimum properties is obtained for the sample post cured at $130^{\circ}C$ for 5 h ours after curing at $80^{\circ}C$ for 2 hours and with 0.5 weight % silane coupling agent.

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Analysis of Insulation Aging Mechanism in Generator Stator Windings (발전기 고정자 권선의 절연열화 메카니즘 분석)

  • 김희동
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.15 no.2
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    • pp.119-126
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    • 2002
  • The mica/epoxy composite used in generator(rated 22 kV and 500 MW) stator windings was aged at 180$\^{C}$ for up to 1000 hours in air and hydrogen. The degradation mechanism was investigated through the defect of evolution and microstructural analysis by performing SEM(Scanning Electron Microscope). As the thermal aging time increases, the number of voids per unit volume increases at the mica/epoxy interface of generator stator windings. The aged specimens in hydrogen showed retarded generation and growth of voids. Accelerated aging tests were conducted using the combination of thermal and electrical aging in air and hydrogen. The aging was carried out at a combined stress such as thermal aging at 110$\^{C}$, electrical aging at 5.5 kV/mm and frequencies 420 Hz in air, and electrical aging at 5.5 kV/mm and frequencies 420 Hz in hydrogen (pressure 4 kg/㎠). Thermal and electrical aging generates large voids at the mica/epoxy interface in air. Electrical aging in hydrogen also generates small voids, delaminations and cracks in mica tapes.

A Study on the Relationship between Aging and Partial Discharge Characteristics of the Mica/Epoxy Composite Insulation Systems (l) (Mica/Epoxy 복합 절연계통의 부분방전 특성과 열화 관계에 관한 연구(I))

  • Kang, D.S.;Lee, W.Y.;Park, C.H.;Kwak, Y.S.;Kim, K.Y.
    • Proceedings of the KIEE Conference
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    • pp.976-979
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    • 1992
  • There are lots of problem which are delaminations and partial discharge of insulation materials in high-voltage rotating machines caused by mechanical, electrical and thermal aging. Several experiments have been aiming at finding the useful diagnostic parameters from the partial discharge characteristics by applying a new measurement techniques. This paper deals with the partial discharge characteristics (pulse height, pulse angle, pulse frequency spectrum and time interval), which may be a useful diagnostic concept in predicting insulation condition of mica/epoxy composite insulation materials, by using several measurement equipments (frequency spectrum analyzer. multichannel analyzer and time interval analyzer).

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