Space charge and breakdown characteristics of XLPE/BNNSs nanocomposites

Cross linked polyethylene (XLPE) has the excellent insulation properties, but which is easy to accumulate space charge under the electric field owing to its low thermal conductivity. Boron nitride nanosheets (BNNSs) with high thermal conductivity were introduced into XLPE matrix to improve the thermal conductivity and electrical properties of the composite. XLPE/BNNSs nanocomposites were prepared by the melt blending method. The basic characteristics of nanoparticles and composite samples were characterized by FTIR and SEM. Space charge and DC breakdown characteristics of XLPE/BNNSs nanocomposites were studied. The experimental results indicated that the introduction of BNNSs suppressed the accumulation of space charge and enhanced the DC breakdown strength of dielectric. The space charge accumulation in the XLPE/BNNSs nanocomposites was significantly reduced and the charge amounts in the material were 0.67x10^-5 C and 0.71x10^-5 C with doping concentration of 0.1 wt% and 0.5wt%. With the increase of doping concentration, the inhibition effect of space charge in the composite weakened. This is mainly due to the formation of deep traps at the interface between the electrode and the composite material, forming a "charge barrier effect" that suppressed charge injection. With the concentration increases, the "charge barrier effect" becomes weakened and charge amounts in the material increased. In addition, the breakdown strength of the XLPE/BNNSs nanocomposites first increases and then decreases with the increase of BNNSs concentration. When BNNSs concentration was 0.5wt%, the DC breakdown strength of XLPE/BNNSs composite reaches the 403.8 kV/mm, which is about 31% higher than that of pure XLPE. This is mainly because the interaction zone between XLPE matrix and nano filler captures a large number of charge carriers and inhibits the carrier transport.