## 1 Introduction
The microcapsule technology refers to using the repairing agent encapsulated in microcapsules to repair the defect in the matrix [1]. The results of many studies show that at the appropriate size and concentration, the microcapsule can withstand the effects of high temperature and stress, and has better repair ability [1; 22; 31]. Moreover, the microcapsule in composite can concentrate stress, thus attracting and repairing the crack defect [17; 19]. However, these studies pay more attention to the mechanical performances of materials, and do not involve the field of electrical insulating materials. In addition, the analysis of the typical physicochemical and electrical performances of materials before and after doping microcapsules are lacking. At present, there are few reports about external self-healing insulating materials [18; 19; 20], and the application prospects in the electricity field are not considered in most of the research on microcapsules [20; 22]. In the aspect of simulation, the static stress distribution of microcapsules used for epoxy resin insulating material was simulated [32]. The results confirmed that the internal stress of insulating material can lead to the rupture of microcapsule, thereby completing the repairing behavior. However, it does not involve the repairing ability of actual insulating material. In terms of experiments, the ability of microcapsules to repair electrical tree damage in epoxy resin was studied [33]. The results showed that the microcapsules can not only repair the damaged area, but also delay the development of electrical trees, but the change rules and mechanism of typical performances are still insufficient. In addition, the migration behavior of superparamagnetic nanoparticles was used to repair the electrical tree damage in polymers, while ensuring that the basic electrical properties of the material were not affected [34]. However, this method requires the stimulation of the external magnetic field, which belongs to the inductive repair system, and there is still a certain gap with the active self-healing target of insulating materials. Therefore, the research on the self-healing polyethylene insulating material remains to be deepened. In this paper, the preparation methods of microcapsule and polyethylene composites were creatively explored and improved to meet the self-healing ability requirements of insulating material. Based on the successful preparation of microcapsule/polyethylene insulating composites, the ability to self-heal structural damage, such as mechanical and electrical damage, was proven by electrical tree, scratch, and breakdown tests. Moreover, the appropriate self-healing conditions of composites were explored. Furthermore, considering the application requirements and performances of polyethylene insulating materials, the crystallinity, volume resistivity, permittivity, and space charge characteristics were selected as the important typical performances to study. The change mechanism of typical performances was innovatively studied from the preparation technology of polyethylene and the doping of microcapsules. In addition, the effect mechanism of doping microcapsules on the typical electrical performances of polyethylene was emphatically analyzed, based on the crystallinity of the matrix, interface, and impurity characteristics of the microcapsule. The pioneering work in this paper can provide an experimental and theoretical basis for optimizing the performances of self-healing insulating material. Besides, the results can be widely applied to plastic polymer insulating materials. Furthermore, this study can provide new ideas for the development of solid insulating materials and self-healing materials.