# Repair Performance of Self-Healing Microcapsule/Epoxy Resin Insulating Composite to Physical Damage
## 3 Results and Discussion
### Repair Performance of Mechanical Damage
#### 3.1.3 Change of Insulation Strength to Scratch Damage
Therefore, the physical damage (such as a scratch) has a greater impact on the electrical breakdown characteristics of insulating material. And the degradation of insulation property is permanent and cannot be recovered by itself. Compared with the pure sample, the insulation strength of the composite obviously rises after heating. Moreover, the breakdown strength of composite can be restored to about 83% of its initial state. The microcapsule can not only repair the physical structure of damage site, but also eliminate the impact of damage on the electrical insulation property of the epoxy resin. On the one hand, the thickness of the defect in the breakdown direction is increased by the filling ability of the microcapsule, improving its microstructure. In other words, the repair ability of the microcapsule can inhibit the distortion and concentration of the electric field at the damage site. On the other hand, the dielectric constant of the repair product (PDCPD) is about 2.78 which is closed to that of epoxy resin (about 3). Therefore, the repair product can effectively uniform the local high electric field and reduce the electrical-mechanical stress of the damage site [11]. Thus, the development of electrical breakdown can be effectively inhibited. In addition, the local state can be introduced by the interface area between the repair product and matrix martial. The discharge energy initially concentrated on the defect can be dispersed by the charge transport of the lower barrier around the local state [1]. Therefore, the electrical insulation property of damaged composite can be restored after repair. Based on the self-healing mechanism, the incomplete repair phenomenon of breakdown strength in composite is explained in this paper. On the one hand, the reaction rate of repairing agent is too fast and the scope of scratch damage is relatively large. So, the reaction process of the repairing agent may have been completed when the damaged part is not completely covered by the repairing agent. In other words, a part of the physical damage gap is still retained, which is similar to the repair result in Figure 2h. Moreover, as shown in Figure 5d (i.e., the reaction result of cross-section), the surface of the product is uneven and there is a physical difference between the product and the matrix. Thus, there are still some physical defects in the damaged area after repair. So, the insulation performance of the material cannot be restored to its initial state. On the other hand, although the electrical properties of PDCPD and epoxy resin are similar, there are still some differences in the material properties. The density of PDCPD (about 1.03 g/cm\({}^{3}\)) is less than that of epoxy resin (about 2 g/cm\({}^{3}\)), so the local low-density area will be formed in the repair site [5]. Thus, the disorder of structure and the density of charge trap are increased, reducing the electrical insulation property. Therefore, the breakdown strength of the damaged composite can be raised after the repair, but it still cannot be restored to the initial state. In general, the experiment results prove that the composite can do repair its electrical insulation property. Therefore, the decrease of breakdown strength caused by physical damage in insulating material can be alleviated, improving the reliability of the power system. At present, the research on self-healing insulating material is still in the exploratory stage. Although a small part of insulation strength is sacrificed, composite can quickly restore its insulation performance after damage. Thus, the composite has good research value.