Abstract
Creeping flashover (surface discharge) at oil-pressboard interface is considered a serious failure of the insulation system in power transformers. In this paper, 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°C), 50 °C, 80 °C and 120 °C. 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. Finally, interpretations of the obtained results are presented through a proposed mechanism.
Highlights
Power transformers are considered vital parts in electric power system; generation, transmission or distribution
EXPERIMENTAL RESULTS experimental results considering the effect of temperature on breakdown voltage of nanofilled oil as well as nanofilled oil-pressboard is investigated
The results match with the results presented in [11,12], where the relative humidity of the transformer oil is decreased with increasing temperature that causes increase in the breakdown voltage
Summary
Power transformers are considered vital parts in electric power system; generation, transmission or distribution. The insulating system for these transformers depends largely on oil-pressboard combination which has a high dielectric strength. Oil-pressboard interface is considered the weakest insulation point. As this interface has the lowest creeping flashover dielectric strength. This comes due to the difference in the relative permittivities of transformer oil and the impregnated pressboard, which supports charge growth under high voltage stresses. Creeping flashover stresses are responsible for serious damage of transformer insulating system under normal AC voltage operating conditions [1,2,3,4,5,6,7]. It is found that adding few percentages of nanoparticles to transformer oil forming nanofluid, improving various electrical properties of oil and oil impregnated pressboard
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