# Repair Performance of Self-Healing Microcapsule/Epoxy Resin Insulating Composite to Physical Damage
## 3 Results and Discussion
### Repair Performance of Electrical Damage  
In the actual operation process, the electrical tree is the main factor leading to the insulation failure of insulating material [30]. The electrical tree can cause the irreversible structural damage of micron and above, thus directly threatening the safe operation of power system [30; 31]. Therefore, the self-healing performance to electrical tree can greatly improve the service life of insulating material. However, there are still few reports about it. This paper mainly studies the propagation stage of electrical tree in epoxy resin. The results are shown in Figure 7. From Section 3.1.1, the heating condition is 60 \({}^{\circ}\)C/30 min. This paper observes the panorama of the electrical tree by the mosaic of multiple graphs to ensure the clarity.  
Compared with pure epoxy resin, the size of the electrical tree in composite is decreased significantly, which is similar to the result in [23]. In addition, the electrical tree in composite tends to develop into a microcapsule and branches near the microcapsule. It can be concluded that the local electric field can be affected by the microcapsule, which attracts the propagation of the electrical tree. When the electric tree develops into the microcapsule, it can break the wall structure of the microcapsule and consume some energy. The residual energy will turn into a new branch, thus the propagation of the electric tree is inhibited. On the other hand, the continuity of the original structure in epoxy resin can be destroyed by microcapsule, thus hindering the propagation of the electrical tree. Therefore, the electrical tree in the composite tends to develop towards the microcapsule area, and its overall size is decreased.  
Figure 7: Morphology of the electrical tree. (**a**) Unheated pure epoxy resin. (**b**) Heated pure epoxy resin. (**c**) Unheated composite. (**d**) Heated composite.  
After heating, the morphology of electrical tree in pure epoxy resin has no obvious change. In composite, except for the main branch of electric tree, the other branches disappeared after heating. Moreover, the width of the main branch in the composite is decreased after heating. Thus, the composite exhibits the obvious self-healing ability to electrical damage. The repair mechanism is similar to that described in Section 3.1, the wall structure of the microcapsule can be broken by the electrical tree, while the core material (repairing agent) can flow into the tubules of the electrical tree through the action of capillary and molecular diffusion. Thus, the partial tubules of the electric tree are filled with repaired product. In addition, due to the dielectric constant of the reaction product being close to that of the epoxy resin, the compatibility between the PDCPD and the matrix is good. Therefore, the local high electric field is weakened, which can further inhibit the development of the electric tree.  
Due to the influence of the voltage condition in this paper, the size of the electrical tree is relatively large. Thus, the repairing agent cannot completely repair all the tubules of the electrical tree. However, the temperature and electric field coexisted in the actual operation of the epoxy resin insulating material. And the propagation time of the actual electrical tree is longer [23; 30]. Therefore, the repairing agent in the microcapsule has a good opportunity to repair the electrical tree in its early stage. In other words, on the premise of reasonable control of the microcapsule concentration, epoxy resin insulating composite is fully capable of repairing the electrical damage.  
The damage to the electrical tree has been regarded as an irreversible permanent defect [24]. In this paper, the microcapsule can not only inhibit the propagation of electrical tree, but also repair the tubules of electrical tree effectively. It has good application value in reducing the harm of electrical damage to insulating material.