Effects of high temperature and high electric field on the space charge behavior in epoxy resin for power modules

In this paper, space charge behavior over a large range of electric field and temperature, of two kinds of epoxy resins are investigated using an improved pulsed electro-acoustic method. Significant influence of high electric field and high temperature on the space charge accumulation in epoxy are found. Hetero charge accumulation starts to build up at 80 °C under 120 kV/mm for amine-type hardener cured epoxy (EP-AM), while at 140 °C under 60 kV/mm for anhydride-type hardener cured epoxy (EP-AH). The accumulated charge increases with the increasing of electric field and temperature. The maximum enhancement of local electric field of is 135 and 123 % at 140 °C for EP-AM and EP-AH, respectively. Quantum chemical calculation is performed to clarify the mechanism of space charge characteristics in the two types of epoxy. It is indicated that ionization of remnant unreacted hardener and electrode injection may be the main sources of space charge. The interaction between molecular chains of EP-AH is stronger than that of EP-AM, which makes it have better space charge characteristics even under high temperature.