Space Charge Accumulation Characteristics of LDPE/TiO2 Nanocomposites under Thermal Aging

Space charge gradually accumulates in the polyethylene insulated cables and directly threatens the stable operation of cables under the high voltage direct current (HVDC) field. In addition, the degradation of low-density polyethylene (LDPE) under thermal aging can increase the space charge accumulation, but the nanoparticles can enhance the ability of LDPE to suppress space charge. However, the ability of nanocomposites to suppress space charge under thermal aging needs to be further studied. In this paper, the space charge accumulation characteristics and the crystallinity of pure LDPE and LDPE/TiO2 samples under thermal aging were carried out with a pulse electro-acoustic method (PEA) system and a differential scanning calorimeter (DSC). It is concluded that the TiO2 nanoparticles can improve the crystallinity of LDPE, and the ability of LDPE/TiO2 to suppress space charge is significant with the TiO2 mass concentration of 1wt%. In addition, thermal aging can damage the microstructure and reduce the crystallinity of materials, increasing the sources of space charge. Combining the theories of interfaces, charge traps and electrode injection barrier, it can be concluded that the TiO2 nanoparticles can decrease the sources of space charge, and the ability of LDPE/TiO2 to suppress space charge is mainly related to the increase of crystallinity. In general, thermal aging has an important influence on the space charge characteristics in LDPE, and TiO2 nanoparticles can suppress space charge and delay the process of thermal aging. Therefore, LDPE/TiO2 nanocomposites still can suppress space charge under thermal aging.