To overcome the degradation of insulating properties caused by the water tree aging of cross-linked polyethylene (XLPE), a self-repairing material for XLPE based on a microcapsule system is proposed. Three-layer shell nucleus microcapsules/XLPE composites with different microcapsule doping content are prepared. The water tree aging experiments are carried out using the water-needle electrode method to analyze the ability of microcapsules to repair the damaged areas of water trees. The results show that, compared with the XLPE material without microcapsules, the electrical properties of composites decline significantly when the doping concentration of three-layer shell nucleus microcapsules is large. When the doping concentration is 1.0 wt%, the microcapsule/XLPE composite breakdown strength has no noticeable change, and the dielectric loss factor does not change significantly, the space charge density decreases, and the space charge properties have been improved considerably. When the water tree branch develops to the position where the microcapsules are located, the microcapsules will rupture and release their internal repair materials and catalysts and react with water to produce an organic silicone resin to fill the water tree cavity, which can achieve an excellent self-healing effect. In addition, the nano-SiO₂ on the surface microcapsules can make the microcapsules and matrix better integrated, which avoids the microcapsule accumulation that tends to occur when incorporating microcapsules, thus improving the repair rate.

This paper proposes a self-repairing material for cross-linked polyethylene (XLPE) based on a microcapsule system to solve the problem of insulation degradation caused by water tree aging. The microcapsules are extrinsic self-healing systems, which not only have good stability and high repair rates but also have little impact on the performance of the matrix. Plasma-modified tri-layer shell-nucleated microcapsules/XLPE composites were prepared by room temperature air radio frequency plasma discharge, and their insulation properties were tested to analyze the effect of microcapsule doping content on material properties. The accelerated water tree aging experiment was carried out by water needle electrode method, and the repair capability of microcapsules to water tree damage area before and after plasma modification was analyzed. The results show that compared with pure XLPE samples, when the content of microcapsules is 1.0 wt. %, the AC breakdown field strength and DC conductivity of the composites change little, and the dielectric properties of composites are improved. When the water tree breaks the microcapsule wall, due to the capillary effect, repair solution and catalyst flow into the water tree branch damage channel and react with water to repair the water tree damage. The average water tree length of plasma-modified microcapsules/XLPE specimens after water tree aging was reduced by 24.86% compared to non-plasma-modified microcapsules/XLPE specimens. The outermost layer of plasma modified microcapsules is nano-SiO2 modified by plasma hydroxylation, which can graft more silane coupling agents, so that the distribution of microcapsules in XLPE matrix is more uniform, the agglomeration of microcapsules is reduced, and the water tree repair ability of composite materials is improved.