Dielectric properties and space charge behavior of MgO-epoxy nanocomposites

Epoxy resin with magnesium oxide filler has already shown a reduced space charge accumulation compared to neat epoxy and composites with other nanofillers. This paper addresses the changes in the structure due to the introduction of surface functionalized nano-MgO into polymers and possible explanations for the unique dielectric behavior. Short term DC breakdown tests were performed alongside space charge measurement and dielectric spectroscopy. The breakdown strength was measured for negative DC voltages with Rogowski shaped electrodes immersed in oil, in order to prevent surface flashover. The base polymer is a commercially available bisphenol A epoxy with anhydrite hardener. As filler material we use magnesium oxide powder with an average particle size of 22 nm and alumina filler with 50 nm average diameter as comparison. The particles were surface modified with a silane coupling agent, in order to achieve a uniform dispersion of particles in the host material. Neat epoxy samples were used as a reference. It is shown that the superior space charge behavior did not reflect on the short term DC breakdown strength however. MgO-epoxy exhibited better short term breakdown results than neat epoxy, but lower breakdown values than epoxy filled with nano alumina.