Research on aging parameters of XLPE cable based on isothermal relaxation current

Abstract

Dielectric response is closely related to the aging status of XLPE cables, and the isothermal relaxation current (IRC) has been applied to find out the change trend of cable insulation as a non-destructive method. In this paper, 4 groups of XLPE cable samples (16 cables in total) are artificially acceleratedly aged with different time interval at 120, 140 and 160°C, respectively, and their IRC curves are measured by a micro-current device. The results show that with the increasing aging time, IRC curves decrease slower and the absolute values of steady current become larger. In order to quantify the aging characteristics of XLPE cables, the trap parameters calculation theory is employed to work out the peak trap level of different polarization types. The experiment results show that the peak trap level of bulk polarization (type 1) remains stable and is around 0.76eV which is considered to be independent of aging degree. As the aging time increases, the peak trap level of amorphous crystalline relaxation (type 2), which is from 0.785eV to 0.82eV, increases at low temperature (120°C) due to the breaking of molecular chain and decreases at high temperature (more than 140°C) due to the over cross-linking. The peak trap level of impurities interface relaxation (type 3) is highly influenced by aging temperature, which is most sensitive to the aging degree of power cable. It is considered that IRC can be used as a practical way to judge cable insulation in the future.