Breakdown mechanism Analysis of Silicone Oil Flocculation in XLPE Cable Terminations

In order to find out the fundamental cause of terminal breakdown of a porcelain-covered oil-filled cable for a 220 kV cable line, a theoretical model of particle phase flow was adopted to analyze the breakdown mechanism by means of finite element simulation. The results show that the breakdown of cable terminal was caused by the flocculation produced by the aging of the silicone oil filled material. When the critical state of the flocculation was reached, the grounding channel was formed along the stress cone, and the electric field in the cable terminal was distorted. The electric field intensity of cable insulation had reach 8.25kV/mm, which was 13.4 times that of normal operation. Under the combined action of high electric field and moisture, many water tree had appear on the outer surface of the cable insulation layer, which leads to the breakdown of the cable insulation layer on the top of the stress cone. The research results can provide an important reference for the design and maintenance of HV and UHV cable termination.