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In this paper, the role of the accumulated surface charge on the surfaces of nanoparticles on breakdown strength for liquid and solid dielectrics is presented. The breakdown strengths of a nanofilled liquid dielectric and a solid dielectric are evaluated. The evaluation was conducted considering different nanoparticle material types with different nanofiller loadings. Accordingly, the preparation of transformer oil nanofluid and silicone rubber nanocomposites was performed with different nanofillers of the same average particle size. Breakdown voltage was measured for all the prepared samples, both liquid and solid. The interpretation of the obtained results is presented. [ABSTRACT FROM AUTHOR]

Studying the effect of adding nanosized ZrO2 to mineral transformer oil on the AC breakdown voltage is presented. The study is carried out considering different concentration levels of nanosized ZrO2. These concentrations are 0, 0.001, 0.002, 0.003 and 0.006%w. The AC breakdown voltage of both nanofilled and base oil is measured according ASTM D1816 standard at room temperature. The evaluation is carried out based on AC breakdown voltage for the nanofilled and base oil considering average and Weibull statistical techniques. Both 50 and 10% breakdown voltage probabilities are obtained and analysed for all samples. Also, the effect of temperature (to take the effect of real operating conditions) on breakdown voltage of base and nanofilled oil is experimentally evaluated. The studied temperatures are 50, 80 and 130°C. The obtained results show that the performance of nanoparticles is significantly affected by increasing the temperature of nanofilled transformer oil. Finally, a proposed mechanism for the effect of temperature on the nanofluids breakdown strength is introduced. [ABSTRACT FROM AUTHOR]

This study presents theoretical as well as experimental studies in order to obtain interpretations about the role of nanoparticles in the breakdown mechanism of transformer oil. The published breakdown mechanisms for nanofilled transformer oil are briefly discussed in order to highlight the points of agreement and disagreement with these mechanisms. Moreover, a proposed breakdown mechanism for nanofilled oil is presented depending on a proposed particle charging mechanism that is theoretically discussed and experimentally validated. Finally, the obtained experimental results prove the efficacy of the proposed theoretical mechanisms. [ABSTRACT FROM AUTHOR]

• The effect of thermal aging on flashover voltage of unfilled oil/pressboard is evaluated. • The effect of thermal aging on the flashover voltage of nanofilled oil/pressboard is evaluated. • The effect of paper coating on the performance of nanofilled transformer oil is investigated. • The obtained results are validated using finite element method. The service life time of oil filled transformers is mainly dependent on its insulating system; either the mineral oil or oil/paper insulation. Thermal aging of these transformer insulating systems is carried out in this work. Accelerating aging is achieved by inserting the samples in an electric oven at 120 °C for 8 weeks. The effect of aging 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 aging 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 aging 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. [ABSTRACT FROM AUTHOR]

• A proposed breakdown mechanism of nanofilled transformer oil is presented for the first time. • The proposed mechanism is based on electric field distortion. • Effect of oil temperature is studied and analyzed in the light of the proposed mechanism. • Effect of size, concentration level, and type of nanomaterial is studied. • Electric field distortion in the nanofilled oil is validated using finite element analysis. In this paper, a proposed breakdown mechanism of nanofilled transformer oil is presented. The proposed mechanism is based on electric filed distortion results from charge accumulation over the surfaces of nanoparticles when exposed to external electric field. Different factors affecting breakdown strength of nanofilled transformer oil are considered. These factors are oil temperature, type, concentration levels and size of nanofiller. Therefore, breakdown strength of nanofilled transformer oil is experimentally evaluated at 35, 70, 100 and 130 °C to simulate the real operating conditions from no load to heavy load. Accordingly, preparation of nanofilled transformer oil samples is carried out considering different nanofiller material types and concentration levels. The adopted nanofiller material types are SiO 2 , TiO 2 , and ZrO 2 considering the same particle size of 25 nm. The selected material types have different relative permittivities of 4.3, 70 and 100 for SiO 2 , ZrO 2 , and TiO 2 , respectively. The studied nanofiller concentration levels are 0.05, 0.1, 0.2, and 0.4 g/L. Also, the effect of particle size on breakdown strength is studied considering TiO 2 nanoparticles of 25 nm and 100 nm particle sizes at the adopted concentration levels. The breakdown strength test is carried out on all prepared samples according to ASTM D1816 standard for all prepared samples. The evaluation of breakdown strength is based on average breakdown voltage. Electric field distortion in the nanofilled transformer oil is validated using finite element analysis. The obtained results show that concentration levels, type, and size of nanofiller as well as oil temperature have a significant effect on breakdown voltage of nanofilled transformer oil. [ABSTRACT FROM AUTHOR]