Polymer nanocomposites as insulation for HV DC cables - Investigations on the thermal breakdown

With the advent of nano-particle fillers in insulating materials, the insulating materials of superior quality have come to fore. In the recent past, nanocomposite LDPE/XLPE (low density polyethylene/cross linked polyethelene) power cable dielectrics have been synthesized. A preliminary evaluation of these new class of materials seem to show that, addition of small amounts of sub-micron inorganic fillers improved the dielectric properties of the composite, in particular, the volume resistivity, and the dc breakdown strength. The thermal behaviour, for example, the stability of composites against decomposition and ensuing electrical failure, do not seem to have been addressed. In a conventional XLPE insulated cable, the average thermal breakdown strength and maximum temperature at the onset of breakdown were seen to be markedly lower than the corresponding intrinsic breakdown strength and decomposition temperature. In the present paper, the Authors have presented and demonstrated the methods of estimating the limiting thermal breakdown voltages on a few nanocomposite materials used as power cable insulation. Experimental data on the volume resistivity reported in recent literature has been used in the series of computations. Nanocomposites of LDPE doped with small amounts of nano-particles of MgO, are chosen. The results show a considerable improvement in the thermal maximum voltage and other related parameters.