Effect of Cryogenic Temperature on DC Electrical Tree Initiation Characteristics of Epoxy Nanocomposites

The widely used epoxy resin for high temperature superconducting (HTS) HVDC transmission system suffers the issue of electrical tree aging under high electrical field. Improving the DC electrical performance of epoxy resin at cryogenic temperature is the key to the safe and stable operation of HTS transmission. In this paper, electrical tree initiation characteristics at room and cryogenic temperature are tested. Moreover, thermogravimetric analysis (TGA) characterization of nanoparticles is carried out. The results show that the thermogravimetric process of nanoparticles modified with KH560 can be divided into physical and chemical thermogravimetric process, which indicates KH560 can effectively modify the surface of nano-alumina. With the increase of applied voltage cycles, the probability of tree initiation increases until all samples are triggered. At room temperature, it is found that the higher content of nano-alumina has the lower the tree initiation probability. In addition, the probability of DC tree initiation at cryogenic temperature is lower than that at room temperature. Furthermore, the tree initiation probability at 1 kV/s is much higher than that at 0.1 kV/s at both room and cryogenic temperatures.