Temperature Driven to Form In Situ Adaptive Graded Permittivity in Epoxy Vitrimers for Improving AC Surface Breakdown

Abstract

Functionally permittivity-graded polymer composites are expected to be used as a solid dielectric for uniformizing the electric field near the metal electrode. In this article, epoxy vitrimers are employed to mitigate the electric field stress near the heating high-voltage (HV) electrode via a permittivity gradient induced in situ by a temperature gradient, thus enhancing the ac surface flashover voltages at high temperatures. Specifically, we uncover a dramatic acceleration in stress relaxation that arises from the topological rearrangement of the epoxy vitrimers, which causes a significant increase in the dielectric constant at high temperatures. The ac surface flashover voltages, dielectric constant, and electric field distribution of the epoxy vitrimers depending on temperature are studied. The epoxy vitrimers containing abundant $\beta $ -hydroxy ester groups show stronger dielectric constant-temperature characteristics than that of the polymer filled with ceramic particles, with a 13.5% rise in the surface flashover voltage as the temperature of the HV electrode increases from room temperature (RT) to $100~^{\circ }$ C, 26 times higher than that of the epoxy vitrimers containing few $\beta $ -hydroxy ester groups. The maximum electric field near the heated HV electrode of the “ ${V}_{{2}}$ ” decreased by 46%, which is the main factor in increasing the ac surface flashover under a temperature gradient. The work presented in this article offers some assistance for the application of environmentally friendly polymer insulation materials in HV electrical equipment.