Electrical Insulation Properties of Nanocomposites with SiO2 and MgO Filler

In this paper, we attempt to improve the electrical characteristics of epoxy resin at high temperature (above 80 degrees C) by adding magnesium oxide (MgO), which has high thermal conductivity. Scanning electron microscopy (SEM) of the dispersion of specimens with added MgO reveals that they are evenly dispersed without concentration. The dielectric breakdown characteristics of SiO2 and MgO nanocomposites are tested by measurements at different temperatures to investigate the filler's effect on the dielectric breakdown characteristics. The dielectric breakdown strength of specimens with added SiO2 decreases slowly below 80 degrees C (low temperature) but decreases rapidly above 80 degrees C (high temperature). However, the gradient of the dielectric breakdown strength of specimens with added MgO is slow at both low and high temperatures. The dielectric breakdown strength of specimens with 0.4 wt% SiO2 is the best among the specimens with added SiO2, and that of specimens with 3.0 wt% and 5.0 wt% MgO is the best among those with added MgO. Moreover, the dielectric strength of specimens with 3.0 wt% MgO at high temperatures is approximately 53.3% higher than that of specimens with added SiO2 at 100 degrees C, and that of specimens with 5.0 wt% of MgO is approximately 59.34% higher under the same conditions. The dielectric strength of MgO is believed to be superior to that of SiO2 owing to enhanced thermal radiation because the thermal conductivity rate of MgO (approximately 42 W/m.K) is approximately 32 times higher than that of SiO2 (approximately 1.3 W/m.K). We also confirmed that the allowable breakdown strength of specimens with added MgO at 100 degrees C is within the error range when the breakdown probability of all specimens is 40%. A breakdown probability of up to 40% represents a stable dielectric strength in machinery and apparatus design.