الفهرس 
Chapter 1: IntroductionOnly 14 pages are availabe for public view
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Abstract
The service lifetime of oil filled transformer is mainly dependent on its
insulating system; either the mineral oil or oil-paper insulation. Creeping
flashover (surface creeping discharge) at oil-pressboard interface is considered a serious failure of the insulation system in power transformers. In this thesis, creeping flashover voltage at oil-pressboard interface using the concept of nanofluids is experimentally evaluated. The creeping flashover test is carried out using a needle-plate electrode configuration considering 5 mm gap spacing. Three different types of nanofiller (CuO, MgO and ZnO) with different concentration levels (0.05, 0.1, 0.2 g/l) are used for enhancing oil-pressboard creeping flashover voltage. The effect of temperature on creeping flashover
voltage is experimentally studied for all nanofiller types at the adopted
concentration levels. The considered temperatures are room temperature (30 oC), 50 oC, 80 oC and 120 oC. These temperatures are considered to study their effect on creeping flashover voltage taking into consideration a wide range of transformer loading. Average of ten creeping flashover voltages is investigated for all studied conditions. Also, Weibull distribution is used for analyzing the creeping flashover voltages at 10% and 50% probabilities for the studied conditions. Also, interpretations of the obtained results are presented through a proposed mechanism. Thermal ageing of these transformer insulating systems is also carried out in this thesis. Accelerating ageing is achieved by inserting the samples in an electric oven at 120 °C for 8 weeks. The effect of ageing is evaluated considering different tests. Firstly, the creeping flashover voltage of oil-pressboard is studied considering epoxy coated and non-coated pressboards. Also, the effect of thermal ageing on the breakdown voltage of oil-kraft paper insulation as well as transformer oil is carried out. All the aforementioned tests are performed considering unfilled transformer oil (base oil) as well as the same base oil modified by adding 0.08 g/l of MgO nanofiller. The effect of thermal ageing considering all the studied cases is discussed and interpreted. Finally, it is found that the epoxy coating and nanofillers significantly affect the performance of oil paper insulation system.