Partial discharge measurements in distribution class extruded cables

Several distribution-class extruded-cables subjected to laboratory-accelerated aging were examined for partial discharges (PD). The cables were subjected to different load cycling while fully immersed in water to obtain different aging conditions. PD initiated in these cables was measured at rated and at elevated voltages. Correlation between the PD-signature and the insulation-defects type was examined. This was achieved by comparing the PD frequency, magnitude and phase angles of different insulation defects. Correlation between the PD level and ac breakdown voltage of these cables also is presented in this paper. The same investigations also were repeated on several cables removed from service after 15-20 years of service. Correlation between the PD levels and the cable remaining life also was investigated.