Factors influencing the electrical insulation of glass fiber composite tubes
Palmu, Niina (2021)
2021
Materiaalitekniikan DI-ohjelma - Master's Programme in Materials Engineering
Tekniikan ja luonnontieteiden tiedekunta - Faculty of Engineering and Natural Sciences
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Hyväksymispäivämäärä
2021-10-11
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202109237249
https://urn.fi/URN:NBN:fi:tuni-202109237249
Tiivistelmä
Glass fiber composite tubes are used in high voltage insulators used in power transmission lines, and insulating tools used in the maintenance of live apparatus. Composite tubes can be hollow or foam-filled and they consist of glass fiber reinforced polymer. They are produced by pultrusion, which is a process used to manufacture continuous, constant cross section profiles. Main functions of high voltage insulators are support the weight of the structures and insulate the live conductors. This thesis examines factors influencing the electrical insulation of glass fiber composite tubes. The main goal is to study how different materials and structures of the tubes affect electrical insulation and mechanical properties.
In the literature research, current materials used in the insulators and their important properties are explored. In addition, a survey of material selection was conducted for material suppliers. The main findings for glass fibers were the effect of boron content on strength and formation of brittle fractures, the effect of seeds in the glass fibers on leakage currents and the compatibility of sizing with the resin. In case of the resins, the most important property was found to be moisture absorption, which affect leakage currents and the formation of brittle fractures.
In the experimental part, the structure of the composite tubes is examined by microscopic examination and dye penetration test. Mechanical properties are studied with bending and compression test and electrical insulating properties by dielectric test. Studied materials consist of combinations of different glass fibers and resins. The glass fibers have varying boron content and sizings. The resins used were polyester, vinyl ester and epoxy based. Tubes have three different lay-ups.
Test results showed that the glass fiber sizing has clear effect on structural integrity and mechanical properties, but not in electrical insulation. Boron-containing glass was found to be inferior to boron-free in both mechanical and electrical insulation properties. Of the resins, epoxy performed best both in electrically and mechanically. Polyester cannot be recommended on electrical insulation applications because of its low resistance to moisture. The number of layers does not affect electrical insulation, but the smaller layer number have degrading effect on mechanical properties. The addition of glass tissue impaired the electrical insulation properties after the moisture exposure, but its effect on the mechanical properties would need further studies.
In the literature research, current materials used in the insulators and their important properties are explored. In addition, a survey of material selection was conducted for material suppliers. The main findings for glass fibers were the effect of boron content on strength and formation of brittle fractures, the effect of seeds in the glass fibers on leakage currents and the compatibility of sizing with the resin. In case of the resins, the most important property was found to be moisture absorption, which affect leakage currents and the formation of brittle fractures.
In the experimental part, the structure of the composite tubes is examined by microscopic examination and dye penetration test. Mechanical properties are studied with bending and compression test and electrical insulating properties by dielectric test. Studied materials consist of combinations of different glass fibers and resins. The glass fibers have varying boron content and sizings. The resins used were polyester, vinyl ester and epoxy based. Tubes have three different lay-ups.
Test results showed that the glass fiber sizing has clear effect on structural integrity and mechanical properties, but not in electrical insulation. Boron-containing glass was found to be inferior to boron-free in both mechanical and electrical insulation properties. Of the resins, epoxy performed best both in electrically and mechanically. Polyester cannot be recommended on electrical insulation applications because of its low resistance to moisture. The number of layers does not affect electrical insulation, but the smaller layer number have degrading effect on mechanical properties. The addition of glass tissue impaired the electrical insulation properties after the moisture exposure, but its effect on the mechanical properties would need further studies.