Effects of Thermal Properties on Insulation Breakdown Behaviors of Epoxy/AlO Composite With Boron Nitride Doping

Temperature gradient generated by a huge current load is an adverse situation that insulation components of high-voltage (HV) apparatuses have to withstand. It could induce thermal stress, mechanical crack or even dielectric breakdown in epoxy-based insulation. In this article, micrometer-sized hexagonal boron nitride ( ${h}$ -BN) particles with high thermal conductivity were doped into the epoxy/Al2O3 composite to regulate its thermodynamics and further improve the insulation performance under a temperature gradient. The dielectric properties, ac breakdown strength, and electrical treeing degradation were studied with varying volume ratios of Al2O3 and BN. Results show that when the volume ratio of Al2O3 and BN reaches 6:4, the thermal conductivity increases to 1.68 W/( $\text {m}\cdot \text { K}$ ). The introduction of BN particles improves the ac breakdown strength and electrical tree breakdown time of epoxy/Al2O3 composite. The effects of BN doping were analyzed by phase field simulation, and results show that the epoxy/Al2O3/BN compounds are able to increase the number of discharge channels, improve the thermal diffusion efficiency, and reduce the internal stresses, thus enhancing the insulation performance of the epoxy composites.