Studies of the polarization/depolarization current characteristics of XLPE cable

Abstract

Cross-linked polyethylene (XLPE) insulation cable is the main type of cable in use now. Its main insulation is aging with the increasing of service years. This problem seriously affects the stability of the power system, particularly for the distribution cables. Therefore, the diagnosis of XLPE insulation cables has important social and economic significance. Polarization and depolarization current (PDC) measurement, a non-destructive dielectric response analytic method based on the dielectric slow response theory, can directly and effectively obtain the polarization information, which is closely related to dielectric states. Many researchers pay much attention to this diagnosis method. Firstly, this paper analyzes different types of polarization/polarization and notes three main types in XLPE based on the dielectric polarization theory. Meanwhile, the paper considers overheat and water tree as the main reasons for distribution XLPE cable aging. Based on the above analysis, this paper puts forwards three R-C series branch extended Debye model as the basis for computing the aging criterion. Then, we also conducted accelerated thermal aging test, obtaining cable samples of different degrees of aging, and then PDC was tested. By observing the different traits of depolarization curves, this paper can initially determine the age of the cable. In order to verify the results, we also measured three XLPE cables' PDC data in power system and use these conclusions to make the qualitative analysis of its aging condition. In order to describe the degree of aging quantitatively, this paper uses aging factor A and Q. It can be concluded that the more severe the degree of aging of cables, the bigger values of A and Q are.