الفهرس 
صفحة العنوانOnly 14 pages are availabe for public view
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Abstract
IIABSTRACTOil/pressboard interface zone is considered one of the weakest paths in high voltage and large power transformerswith increased possibility of electrical discharge. So, this study aimed to enhancethe flashover strengthof such interface through using the concept of nanofluids. Initially,nanofluids were prepared by mixing and dispersing a certain weight fraction ofnanoparticles into the base transformer oil. Then, pressboard samples wereimpregnated into the nanofluid sample.Two types of nanoparticleshave been used, Alumina (Al2O3) and Titania (TiO2) nanoparticles. These typeshave different values of surface charging.For characterization purpose of applied nanoparticles, zeta potential, atomic force microscopy (AFM)and infra-red spectroscopy (IR) had been applied. Flashover strength of nanofluid impregnatedpressboard was tested for different weight fractions of nanoparticles and was comparedto that of the base mineral oil. Both static oil and oil flow conditions were considered. In each test, the value and polarity of applied high voltage AC at theinstant of flashover was recorded. Weibull distribution was used for analyzing flashoverstrength data. The polarity at which flashover occurred was positive in most of casesstudied, eitherwith oil or with nanofluids. Based on this observation, physical mechanisms have beendiscussed considering the surface charging and double layer modelof nanoparticles as well as double layer formed at oil/pressboard interface. Both Al2O3nanoparticles and TiO2nanoparticles have succeeded in enhancing flashover strength of nanofluid impregnated pressboardunder static conditions. This enhancement was explained in terms of the interface double layer for Al2O3nanoparticles and the electron trapping ability for TiO2nanoparticles.Under dynamic flow conditions, the interface double
IIIlayer around Al2O3nanoparticles became less effective forto enhance flashover strength, whereas the electron trapping ability was kept effective for TiO2nanoparticles