Analysis of low-frequency dielectric loss of XLPE cable insulation based on extended Debye model

Dielectric response technology is an effective method on state detection of dielectric materials. However, when the technology is employed to evaluate the aging extent of the cable, the interpretation of the microscopic mechanism, which leads to changes in the dielectric loss factor spectrum, is lacking in the research. It also does not refine the frequency range with strong polarization loss caused by defects, such as water trees and impurities. In this paper, the loss characteristics of XLPE cable insulation at low frequencies were studied. First, the frequency domain parameters were obtained by the time–frequency domain dielectric conversion principle through the polarization current measurement. Second, the polarization loss and conductivity loss based on the extended Debye model were effectively distinguished. Finally, the frequency domain dielectric spectrum of polarization loss caused by water treeing defects was extracted and discussed. The research results show that in the low frequency range, the conductivity loss and polarization loss of the XLPE cable increase as the aging degree of the cable deepens. Among them, the contribution of polarization loss to the overall loss is gradually increasing. At the same time, the polarization loss (tan δp3) caused by defects, such as water trees and impurities, inside the cable insulation has an obvious effect in the ultra-low frequency band. As the degree of aging increases, the extreme value of tan δp3 increases, and it moves to higher frequencies.