硅脂对硅橡胶电树枝劣化特性的影响机制研究

Electrical tree degradation is one of the main reasons for the decline of insulation performance or even failure of silicone rubber based cable accessories. During the installation of cable accessory, the interface between cable accessory insulation and cable insulation is usually coated by silicone grease. However, the influence of silicone grease on electrical tree degradation is not fully understood. The effect of silicone grease on the electrical tree degradation characteristics of SR was studied in the paper. The results showed that, due to the silicone grease, the electrical tree initiation voltage decreased from 13.5kV to 10.8kV, while the pattern of the electrical tree changed from branch type to bush type. Further analysis were carried out by trap charge characteristic, thermal decomposition analysis and crosslinking density measurement. It was suggested that the break of physical crosslinking and molecular chain caused by silicone grease led to the decline of crosslinking density as well as the increase of free volume and charge mobility. Therefore, due to increased free volume, higher energy of injected charges can be achieved, which consequently led to more broken chains in silicon rubber and eventually a lower electrical tree initiation voltage. At the same time, the charges can also be accelerated to break the molecular chains under weak radial electric field in a larger free volume. Therefore, the pattern of electrical tree was changed from branch type to bush type.