Frequency-Dependent Breakdown Strength of Epoxy Composites: Role of High Thermal Conductivity and Low Dielectric Loss

The degradation of insulation performance in epoxy resin under high-frequency voltage presents a significant barrier to advancing power electronic devices, such as solid-state transformers (SST), to operate at higher frequencies and voltages. Effective management of dielectric heating and heat dissipation within insulation materials is crucial for enhancing high-frequency insulation performance. In this study, an epoxy resin (EP)/boron nitride (BN) composite is developed using a curdlan-assisted gelation process and the breakdown strength was evaluated across a frequency range of 1-20 kHz. The composite achieves an enhanced thermal conductivity of 2.37 W/(m·K) and a 32.8% reduction in dielectric loss at 160°C and 100 kHz, compared to the neat epoxy. It is observed that electrical breakdown due to carrier migration at low frequencies transitions to thermal breakdown induced by polarization loss at high frequencies. The composite effectively mitigates the degradation of breakdown strength in EP as the frequency increased, exhibiting a 24.8% improvement in breakdown strength at 20 kHz compared to EP. Additionally, the thermal runaway boundary under high-frequency and high-voltage conditions is expanded by 29.8% and the design limit of electric field strength under high-frequency conditions is nearly doubled. This work offers valuable insights for designing insulation boundaries in high-frequency power electronic devices.