Research on the defect development of cable accessories under AC voltage

As cable insulation failure usually started with PD activity, a PD detection system based on pulse current was built to study the PD characteristics of typical defects in XLPE cable. To facilitate the test, the oil cup test terminal was used. Considering the installation procedure, three different kinds of insulation defects in cable accessory samples were made, which were knife incision defect, metal floating potential defect and misplaced stress cone defect. Under long time power frequency voltage of U», 1.7U0, 2.5U0 and 3.5U0 (U0=8.7kV), this paper proposed a variety of methods to characterize partial discharge of these samples by PRPD spectrum, δ t spectrum and PSA spectrum. Results showed the δ t spectrum presented a clear distribution of the peak and the sub-peak. The distribution regularity of partition probability in PSA pattern before the breakdown was found that the probability in the area 1.1 as from 50% to 60%, and the probability in the area 3.1 was from 30% to 40%.