Material challenge of MgO/LDPE nanocomposite for high field electrical insulation

Polymeric electrical insulating materials are widely used in various power equipments and cables. Additives and fillers are often adopted to polymeric materials for improving insulating and mechanical properties. Recently, nano-fillers are attracting attentions of many researchers and engineers, since they seem to bring higher potentials for advancement of electrical insulating properties as nanocomposites. This paper reports evaluation results of various insulating properties of a MgO/LDPE nanocomposite, jointly carried out by several organizations, aiming at development of an electrical insulating material for higher DC electric field. The DC breakdown strength and the volume resistivity increased with the addition of MgO nanofillers. The thermally stimulated depolarization current (TSDC) peak that spreads over a wide temperature range was observed in all the MgO/LDPE nanocomposites. Furthermore, by adopting a partial heating method, the wide TSDC peak was resolved into several component peaks and it turned out that one of the peaks was attributed to MgO nano-filler, from which it is suggested that a new trap is generated in the nanocomposites. And it was observed from space charge measurement that addition of MgO nano-fillers suppressed packet-like charges in the nanocomposite. The relative permittivity once decreased slightly by addition of MgO nano-fillers and then increased by more addition of them. The electrical treeing inception voltage increased with increasing MgO nano-filler content and it is also recognized that the tree propagation in the MgO/LDPE nanocomposite was suppressed significantly by the addition of MgO nano-fillers. The partial discharge erosion depth of the MgO/LDPE nanocomposite also becomes smaller than that of base LDPE. It is summarized that addition of a small amount of nano-fillers brought excellent insulating performances of the MgO/LDPE nanocomposite. The MgO/LDPE nanocomposite exhibits promising electrical insulating properties to cope with severe requirements and is expected as a new generation of electrical insulating materials for higher electric field application, especially for DC voltages.