Space-Charge Characteristics in Epoxy Composites Under Square Pulse Wave of Different Polarities With Various Frequencies at Various Temperatures

Space-charge characteristics of the pure epoxy resin (EP) and epoxy-based hybrid composites under square pulse waves of different polarities and frequencies at different temperatures are investigated. A specially built high-speed pulsed electro-acoustic (PEA) equipment for high-temperature testing is used. The square pulse of 40 kV/mm with different polarities and frequencies at 25 °C, 50 °C, and 80 °C, respectively, are adopted. The findings reveal that a negative electric field with a greater frequency and a positive electric field with a lower frequency can increase the space-charge accumulation. At low temperatures, there is no noticeable difference between the pure epoxy and micro-nano hybrid (MN) samples. The MN sample has fewer accumulated charges than the pure epoxy sample under the same electric field of different frequencies at different temperatures. At different temperatures, the electric field inside the pure epoxy sample distorts more severely than the MN sample, and such distortion increases with the temperature. On the other side, the electric field in the MN sample remains steady even at high temperatures. Negative electric fields have a more significant impact on average charge amounts than positive electric fields, especially at higher frequencies. A relevant mechanism is proposed to explain the results.