DC breakdown strength of crosslinked polyethylene based nanocomposites at different temperatures

Polyethylene based nanocomposites have been widely researched for being potential insulating materials in high voltage DC equipment. One of their key properties is the enhanced DC breakdown strength (E_b-DC). For a long time, the E_b-DC of polyethylene nanocomposites has been attributed to the deep charge traps located at the interphase region between the nanofiller and polymer matrix. In this work, we prepared XLPE/Al(OH)₃ nanocomposites with 0.1 to 3 wt% nano-Al(OH)₃ and studied their E_b-DC at 20 to 90 °C. The results show that the XLPE/Al(OH)₃ nanocomposites possess significantly increased E_b-DC, although having a large amount of shallow charge traps, and more likely causing homocharge injection. The results of breakdown tests show that E_b-DC first increases and then decreases at 20 to 70 °C with increasing nanofiller while it shows a totally opposite trend at 90 °C. E_b-DC decreases dramatically with increasing temperature, a crossover phenomenon of E_b-DC appears at about 80 °C. The elastic modulus of XLPE/Al(OH)3 at different temperatures was obtained and it shows a similar trend with E_b-DC. Therefore, the mechanical properties influenced by morphology and space charge properties modulated by charge trap characteristics were analyzed to jointly determine the E_b-DC of XLPE/Al(OH)₃ nanocomposites at different temperatures.