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In this study, the dielectric properties of unfilled as well as nanofilled polystyrene-silicone rubber blends are evaluated. Accordingly, the preparation of polystyrene-silicone rubber blends is carried out considering three different concentrations of polystyrene (3, 7 and 10%wt). Also, the preparation of polystyrene-silicone rubber nanocomposites is carried out considering different two types of nanoparticles. These nanoparticle types are TiO2 and SiO2 with the same average particle size of 20 nm. Different nanoparticle concentration levels of 1.5, 2 and 3%wt are studied. The effect of thermal aging on the dielectric properties of unfilled as well as nanofilled polystyrene-silicone rubber samples is evaluated. The samples are subjected to thermal aging for two months at a temperature of 130 °C. The average breakdown strength as well as the breakdown strength at 10% and 50% probabilities is evaluated before and after the thermal aging process. The dielectric response includes relative permittivity and dissipation factor which measured and evaluated under thermal aging. The obtained results show that adding small amount of polystyrene to silicone rubber improves its dielectric properties. Finally, adding small amounts of TiO2 and SiO2 nanoparticles to polystyrene-silicone rubber blends give more improvements in its dielectric properties. [ABSTRACT FROM AUTHOR]

Electric cables play a crucial role in transmission and distribution systems. Polyvinyl chloride (PVC) is extensively used in cable insulation. In this work, PVC samples filled with nanosized ZnO and MgO particles are prepared. The effect of external electric field during sample preparation on the dielectric properties of PVC nanocomposites (NC) is evaluated. Accordingly, the samples are subjected to horizontal and vertical external electric fields during the preparation process. The evaluation is carried out considering different nanoparticle concentration levels. The studied concentration levels are 0.5, 1, 3 and 5 wt% for both adopted nanofiller types. Breakdown strength of the prepared NC samples is measured according to American society for testing and materials standard. Also, relative permittivity and dielectric loss of the prepared NC samples are measured. The evaluation is carried out considering horizontal and vertical electric fields. The obtained results show significant effects on the dielectric properties of the tested samples. Hence, the results show that the external electric field decreases relative permittivity and dielectric loss; however, it increases the breakdown strength of PVC NC. Applied horizontal electric field during sample preparation gives more improvement in dielectric properties of PVC NC compared to vertical electric field. Finally, the interpretation of the obtained results is highlighted and discussed. [ABSTRACT FROM AUTHOR]

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]

Accelerated thermal ageing test on nanocomposites of polyvinyl chloride (PVC/SiO2) is conducted at constant temperatures of 110 °C and 140 °C. Accordingly, different PVC/SiO2 nanocomposite samples with different silicon dioxide (SiO2) filler loading are prepared. The preparation of the samples was carried out based on the solution casting technique. The loading concentrations of SiO2 in the investigating samples are 0, 1, 2.5, 5 and 7.5 wt%. The breakdown strength of the prepared PVC/SiO2 nanocomposite samples is evaluated before and after the thermal ageing test. The evaluation of breakdown strength is carried out based on American Society for Testing and Materials (ASTM) standard. Also, dielectric spectroscopy, which includes dielectric constant (έ) and tangent loss (tan δ) of nanocomposite, is performed before and after the thermal ageing test. Also, the mass losses during thermal ageing of all samples are evaluated. The results show that the breakdown strength, tan δ, and the dielectric constant (έ) of pure PVC and PVC/SiO2 nanocomposites are significantly affected by the thermal ageing test. Adding a small amount of SiO2 nanoparticles to PVC leads to improvement in its dielectric properties before and after the thermal ageing process as compared to the pure PVC. The mass loss of PVC/SiO2 nanocomposite during thermal ageing is less than that of pure PVC and confirms the obtained result from breakdown strength. [ABSTRACT FROM AUTHOR]

Many day-to-day operation decisions in a smart city need short term load forecasting (STLF) of its customers. STLF is a challenging task because the forecasting accuracy is affected by external factors whose relationships are usually complex and nonlinear. In this paper, a novel hybrid forecasting algorithm is proposed. The proposed hybrid forecasting method is based on locally weighted support vector regression (LWSVR) and the modified grasshopper optimization algorithm (MGOA). Obtaining the appropriate values of LWSVR parameters is vital to achieving satisfactory forecasting accuracy. Therefore, the MGOA is proposed in this paper to optimally select the LWSVR's parameters. The proposed MGOA can be derived by presenting two modifications on the conventional GOA in which the chaotic initialization and the sigmoid decreasing criterion are employed to treat the drawbacks of the conventional GOA. Then the hybrid LWSVR-MGOA method is used to solve the STLF problem. The performance of the proposed LWSVR-MGOA method is assessed using six different real-world datasets. The results reveal that the proposed forecasting method gives a much better forecasting performance in comparison with some published forecasting methods in all cases. [ABSTRACT FROM AUTHOR]