Electrical Tree Inhibition Characteristics of AOS Grafted Epoxy Resin Composites Considering the Coupling Effects of High Frequency and Temperature

Abstract

Encapsulation insulation materials for high-frequency transformers endure coupled electrothermal stresses from sustained high-frequency pulsed voltages and elevated operational temperatures, exhibiting inherent limitations in electrical treeing resistance that trigger premature insulation degradation. To address this, 4-acetoxystyrene (AOS) is chemically grafted onto $E$ -51 bisphenol-A epoxy resin (DGEBA) via free radical grafting, forming DGEBA-g-AOS composites with varied AOS contents. The electrical tree growth characteristics under high-frequency (10 kHz) conditions at both room temperature ( $25~^{\circ }$ C) and high temperature ( $90~^{\circ }$ C) are systematically investigated through physicochemical characterization, quantum chemical calculations, and trap property analysis. The results demonstrate that at $25~^{\circ }$ C and 10 kHz, AOS effectively delays electrical tree initiation and propagation by trapping high-energy electrons and increasing trap density. Under $90~^{\circ }$ C and 10 kHz conditions, although the electrical tree growth rate shows no significant reduction, branch complexity decreases, and the damage area diminishes. This study provides critical insights for the development of advanced encapsulation insulation materials in high-frequency/high-temperature transformers.