الفهرس | Only 14 pages are availabe for public view |
Abstract Electrical power cables are an important part of electrical transmission and distribution networks. It is covered with a suitable insulating material, based on the operating voltage level. Underground cables and its accessories are exposed to electrical, mechanical, thermal stress and chemical ageing individually or combined, causing rapid insulation degradation for cables. Recently, the introduction of nanoparticles (NPs) into the base polymer matrix under the name of nanocomposites has approved an improvement in dielectric properties. In this thesis, various PVC/SiO2 nanocomposite samples with different silica (SiO2) filler concentration are fabricated based on the solution casting method. The SiO2 loading concentrations of the prepared samples are 0, 1, 2.5, 5, and 7.5 wt%. The evaluation of breakdown strength is carried out based on the American Society for Testing and Materials (ASTM D149) standard. In addition, the volume resistivity is measured as per IEC 62631-3-1 standard. Also, dielectric spectroscopy, which includes dielectric constant (έ), a.c.conductivity (σac), and tangent loss (tan δ) of the nanocomposite, is performed. The results show that adding a small amount of SiO2 nanoparticles to PVC improves its dielectric properties. In order to examine the performance of nanocomposites for the long term, the dielectric properties of pure PVC as well as PVC/SiO2 nanocomposites were investigated under thermal ageing and after water absorption. In this respect, an accelerated thermal ageing test on polyvinyl chloride (PVC/SiO2) nanocomposites is performed at constant temperatures of 110 °C and 140 °C. Accordingly, the breakdown strength and dielectric spectroscopy of the prepared PVC/SiO2 nanocomposite as well as pure PVC are evaluated during the thermal ageing test. Additionally, the mass loss during thermal ageing of all samples is evaluated. The results show that the breakdown strength, tan δ, Ac conductivity (σac), and the dielectric constant (έ) of pure PVC and PVC/SiO2 nanocomposites are significantly affected by the thermal ageing test. |