Thermal aging status diagnosis of XLPE cable using polarization/depolarization current method

Correctly diagnosing the aging status of cross-linked polyethylene (XLPE) power cable is very important for judging its insulation condition. In order to get XLPE cable samples with different aging status, artificial accelerated aging experiments(aging temperature is 140℃ and aging time is 10 d, 20 d, 30 d, 40 d) were carried out. We also designed a structure to eliminate the surface current and then measured the polarization/depolarization current of aging sample. Based on the measurement data, polarization intensity was calculated. The results show that different PDC curves can judge aging degree to some extent but not practical enough. To quantify the cable aging degree, the aging factor A, a parameter describing the dielectric traps inside the XLPE, is adopted. The results show that A rises gradually with the increase of aging degree. Under 140℃ aging temperature, 20~30 day aging cable is in middle-heavy aging status. Consequently, it is suggested that a power company should carry out PDC test especially for 15 years-old cables.