Thermal characterization of polyethylene-metal oxide nanocomposites used as electrical insulation in HVDC cables

Abstract

The design of insulation for HVDC extruded cables is one of the most challenging issues, mainly due to the dependence of its dielectric properties on temperature, electric field distortion due to accumulation of space charge in the insulation. Polyethyelene-metal oxide nanocomposites are used to achieve the space charge reduction, enhance the volume resistivity and also achieve higher dielectric stress withstand capability. However, the study of thermal ageing characteristics of nanocomposite is very necessary to understand its long term performance and its reliability when used in HVDC extruded power cables. Different metal oxide nanoparticles such as MgO and SiO 2 have been investigated as fillers in low density polyethylene in concentrations of 1 phr to 4 phr (1gm in 100 gm). The surface modification of the oxide nanoparticles were done with Polyethylene Graft Maleic anhydride (PEMAH) and functional methyl, ethyl or octyl silanes. Surface pre-treated nano sized metal particles were dispersed in a rheometer with low density polyethylene at 100 oC for 20 minutes and nanocomposites were prepared. The distribution and dispersion of the nanoparticles in the LDPE is determined by SEM (Scanning Electron Microscopy). The samples were thermally aged at 110o C for 250 hrs and 500 hrs. Studies were carried out by measuring surface resistivity, volume resistivity, melting temperature, deposition temperature using simultaneous thermal analyser. The effect of thermal ageing on the physical and electrical properties of nanocomposites were studied at different ageing hours.