Characterizing trap distribution in LDPE and HDPE based on isothermal surface potential decay measurement

Space charge accumulation plays an important role in the service life and the safe operation of DC cables. Focusing on the distribution character of trapped charges and the traps within polyethylene is of great significance to control the space charge accumulation and improve the safe reliable operation of the DC cables. In this paper, isothermal surface potential decay (ISPD) model which considered the detrapping process of charges in polymeric materials was presented. The surface potential decay properties of low-density polyethylene (LDPE) and high-density polyethylene (HDPE) films were measured under the condition of positive and negative corona charging, respectively. Combining the ISPD model, the trap distribution of LDPE and HDPE were obtained and analyzed according to their morphological characteristics. The results show that there are mainly deep trapped charges in these two materials. And the trap density is nearly 10²¹ m^-3, which is consistent with other reported literatures. The density of shallow traps in LDPE is higher than that in HDPE, while the density of the deep traps is lower. In LDPE, the density of electron-type shallow traps is lower than hole-type shallow ones, while the electron-type deep traps is higher than that of hole-type deep ones. It is indicated that the unique aggregation structure of LDPE/HDPE and different performances of electron/hole conduction may have a significant role in determining the distribution of trapped charges.