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Adding nanoparticles (NPs) to a base polymer matrix which is known as nanocomposites results in improving its dielectric properties. In this paper, the evaluation of polyvinyl chloride (PVC)/silica nanoparticles (SiO2) nanocomposites is carried out considering the effect of water absorption. PVC nanocomposites are prepared considering different filler loadings of SiO2 NPs (1, 2.5, 5, and 7.5 wt%). The preparation of PVC/SiO2 nanocomposites is chemically carried out by casting the solution. The chemical structure of PVC/SiO2 nanocomposites after water adsorption is investigated by Fourier transform infrared (FTIR) spectroscopy. The effect of water absorption is carried out by immersing nanocomposite samples in tap water. The AC breakdown strength of PVC/SiO2 nanocomposites is measured before and after water immersion. In addition, both dielectric constant (έ) and loss tangent (tan δ) are measured considering different frequencies before and after the water immersion. The results show that the dielectric properties of PVC/SiO2 nanocomposites are significantly affected by water absorption, where PVC/SiO2 nanocomposite sample with filler loading of 7.5 wt% is found to have lower water absorption compared to the other adopted filler loadings. Under the effect of water absorption, the breakdown strength of the base and PVC nanocomposite samples is decreased, and its value for PVC nanocomposite still exceeds the base polymer. Finally, the dielectric constant and dielectric loss of PVC samples are increased under the effect of water absorption. The increase in dielectric constant and dielectric loss is small at the higher filler loadings. [ABSTRACT FROM AUTHOR]

Effect of adding nanofillers on transformer oil breakdown voltage and its thermal performance finds a great interest from researchers and scientists. The impact of oil circulation considering oil forced cooling method on nanoparticles stability in transformer oil is investigated. The stability is considered from breakdown voltage and thermal performance points of view. Titanium dioxide (TiO2) nanoparticles are chosen due to the safety of TiO2 nanomaterial as well as its good performance. First, the optimal concentration of nanosized TiO2 at which maximum breakdown voltage of nanofilled transformer oil is determined and chosen to study the effect of oil circulation on breakdown voltage as well as thermal performance of nanofilled oil. Two reduced experimental models are designed. The first model consists of a galvanized steel tank containing TiO2‐nanofilled transformer oil, at the pre‐determined optimal concentration. This tank is designed to simulate the natural oil cooled transformer. However, the second model that uses a similar tank is designed to simulate a forced cooled transformer. This model consists of a tank containing TiO2‐nanofilled transformer oil, at the pre‐determined optimal concentration, and an oil pump. Breakdown voltage and thermal performance considering the two adapted models are measured in a time period of 60 days. [ABSTRACT FROM AUTHOR]

Oil‐paper composite is the main insulation system in oil‐filled transformers. In recent years, the use of nanotechnology to improve the electrical and thermal properties of transformer oil has become a field of research interest. In this paper, the electrical properties such as breakdown strength, volume resistivity, and dielectric response of nano‐filled oil‐paper insulation are evaluated. The evaluation is carried out on a double‐layer of oil‐paper composites insulation. The double‐layer samples are prepared considering different nano‐filler types. The studied nano‐filler types are Pb3O4, Al2O3, and SiO2 with average particle size 25 nm of each. For each nano‐filler type, oil‐paper samples with different concentrations (0.04, 0.06, 0.1, 0.2, and 0.4 g/L) are prepared. The effect of nano‐filler types on the breakdown strength, volume resistivity, and dielectric response of oil‐paper composites are highly evaluated. The results show that the filler types as well as filler permittivity affects the breakdown strength, volume resistivity, and dielectric response of oil‐paper composites insulation. Also, the results show that nano‐filler with high permittivity gives higher improvement in breakdown strength of Oil‐paper composite compared nano‐filler with low permittivity. Finally, the interpretation of all obtained results considering breakdown strength, volume resistivity, and dielectric response is highly reported. [ABSTRACT FROM AUTHOR]

SUMMARY The wind turbine is subjected to lightning due to its geographical location and size. The struck wind turbine suffers from backflow current-overvoltages affected by the grounding system. This issue is highlighted in this paper, and, therefore, the grounding system of the wind turbine is modified. In order to accurately examine the proposed grounding system, we present a model that takes into account both soil ionization and frequency-dependence effect. Also, wind farm components, such as wind turbine down conductor, transformers, surge arresters, overhead, and distributed line, are modeled using high-frequency models. More factors affecting backflow current-overvoltages are analysed such as the lightning inception angle, in-service and out-of-service wind farm, and the number of wind turbines. The simulation is carried out using ATP/EMTP software. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]