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| Effects of Moisture Contents on Electrical Treeing Process in Glass Fiber Reinforced Epoxy Resin |
| Li Jin1, Zhao Renyong1,2, Chen Yun1, Li Tianhui3, Du Boxue1 |
1. School of Electrical and Information Engineering Tianjin University Tianjin 300072 China;
2. State Grid Shandong Zibo Power Supply Bureau Zibo 255032 China;
3. State Grid Hebei Electric Power Research Institute Shijiazhuang 050021 China |
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Abstract Insulating pull rod is a key component of circuit breaker and disconnector of gas insulated metal enclosed switchgear (GIS), which is used to transfer movement from the grounding part to the high voltage part. It needs to withstand the recovery overvoltage and frequent mechanical operation, which puts forward high requirements on the comprehensive performance of the glass fiber reinforced epoxy resin (GFRP) composite. However, many internal breakdown and disassembly failures of insulation rods occurred in recent years, which seriously threaten the reliability of power equipment. In this paper, the influence of moisture content on the electrical tree growth characteristics of GFRP was studied. Combined with the dielectric properties and the hydrolysis characteristics of GFRP with different moisture contents, the mechanism of the electrical treeing process of GFRP was explained from the perspective of electric field distortion and insulation degradation.
(1) Based on the relationship between moisture content and exposure time, it is verified that the moisture diffusion behavior in epoxy resin and GFRP composites conforms to the free diffusion Fick model.
(2) When the pure epoxy resin absorbs moisture, the number of electrical tree channels increased and the color gradually deepened. In details, the growth rate of electrical tree length first increased and then decreased. Moreover, the expansion coefficient and the growth angle of electrical tree decreased and then increased, and the deterioration damage area gradually increased, indicating that electrical tree is more likely to grow along the vertical electric field direction with the increase of moisture content in the sample.
(3) When the GFRP absorbs moisture, the number of electrical tree channels increases. In addition, the electrical tree will also grow along the interface perpendicular to the electric field direction. The growth rate of electrical tree length decreases first and then increases, while the growth rate and the growth angle of electrical tree also gradually increases.
(4) It is found that when the moisture content in epoxy resin and GFRP exceeds 0.08% and 0.1% respectively, the deterioration of electrical tree significantly enhanced, which provided a basis for moisture control during the test, transportation and assembly of insulating pull rod. The fiber-epoxy interface may have defects of varying degrees due to hydrolysis and wet mismatch stress, and the moisture gradient diffusion further causes local electric field concentration, which aggravates the deterioration of GFRP.
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Received: 26 July 2022
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2023, Vol. 38 
