Effects of diffusion activity of injected liquid on water-treeing cables' electrical properties after injection

In order to further understand the rejuvenation mechanism of water tree in cross-linked polyethylene (XLPE) cables, the diffusion activity of rejuvenation liquid in a XLPE cable was investigated in the process of the water-treeing rejuvenation. The diffusion activity of rejuvenation liquid was also analyzed along axial and radial direction in the XLPE cable, and influence factors of the changes of the rejuvenation liquid concentration were discussed in this paper. Firstly, needle-shape defects were previously made inside XLPE cable samples to create water tree in the XLPE layer. The water tree cables were injected with the rejuvenation liquid, and the dielectric loss factor was measured in the process of the rejuvenation. Moreover, the diffusion activity of rejuvenation liquid in the cables was simulated and analyzed by a finite element method. According to the investigation of the diffusion activity of the rejuvenation liquid in the XLPE cable, the minimum effective concentration of rejuvenation liquid is presented. The results indicate that a sharp decline of tanδ values is observed in 4~6 hours and gradually returns to a lower level after injection. The concentration of the rejuvenation liquid is proportional to the cross-sections of cables and the injection pressure. The diffusion efficiency of the rejuvenation liquid non-linearly increases with the injection pressure increasing. Therefore, the diffusion efficiency of the repair liquid is one of the main reasons for electrical properties changes of the water-treeing cable samples. © 2015 Chinese Society for Electrical Engineering.