Epoxy-based ZnO nanocomposites in various configurations: Corona discharges and thermal transition studies

Polymeric epoxy-based nanocomposites have tremendously grown in electronic and indoor high-voltage insulation applications over the last two decades. The interface between the epoxy resin and inorganic fillers surprisingly improves the performance compared to neat epoxy and conventional ceramic insulators. However, several configurations, including the filler loading, filler size, and synthesis process, substantially impact performance. Dielectrics employed in power equipment are often exposed to corona discharges, causing surface erosion and may cause flashover due to prolonged exposure to the discharges. Also, dielectrics must continuously endure heat from leakage currents or surrounding temperatures. The present work examines various configurations of the epoxy/ZnO composites for the corona discharge resistance and thermal stability: the effect of filler loading, preparation method of nanocomposites, and co-filling of nano-micro fillers. The ZnO nanoparticles were disseminated in the epoxy resin using a probe and bath sonicator with and without solvent. It also includes the impact of heated nanoparticles. The corona discharge tests were performed using a set-up similar to CIGRE working group D1.24. The studies of surface degradation were conducted using surface roughness metrics obtained from an optical 3D profilometer. Differential scanning calorimetry (DSC) was used to perform the thermal analyses as per ASTM E1356. It was found that compared to all the filled specimens, the neat epoxy experienced more severe erosion. In addition, the specimen filled with ZnO nanoparticles endured positive corona discharges compared to negative and AC discharges. The specimen prepared with heated nanoparticles without solvent using a probe sonicator showed high heat energy and heat capacity leading to thermal instability. Besides, the interface between nano-micro particles and the host material increases corona discharge resistance and thermal stability.