Breakdown Strength and Electrical Tree in Homo-Crosslinked-Polyethylene Bilayer

The return insulation structure of submarine cable factory joint can be simplified as homo-crosslinked-polyethylene (H-XLPE) bilayer, and its dielectric property under power frequency is the key to the offshore alternating current (AC) electric field transmission system. This paper focuses on the AC breakdown field strength and electrical tree of H-XLPE bilayer insulation by using the power frequency high voltage generator and relevant electrode system. The results show that overall AC breakdown field strength of H-XLPE is lower than that of XLPE. The electrical branches diverge obviously in H-XLPE bilayer, which is not existence in XLPE under the same conditions. There is a homo-junction region in H-XLPE bilayer, which is acted as an electrical tree initiation, then this region would reduce the withstand voltage performance further. This study indicates the effect of H-XLPE bilayer on the factory joint return insulation, which should be fully taken into account in the design of AC submarine cable accessories.