الفهرس 
Thesis MotivationOnly 14 pages are availabe for public view
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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.