Propagation mechanism of electrical tree in XLPE cable insulation by investigating a double electrical tree structure

This paper presents our experiments and analysis of the electrical tree growing characteristics. The relationship between electrical tree propagation and the material morphology in XLPE cable insulation has been studied by researching the structure and growth characteristics of a double structure electrical tree. It has been found that, due to the influence of uneven congregating state, difference in crystalline structure, and the existence of residual stress in semi-crystalline polymer, five types of electrical tree structures (branch, bush, bine-branch, pine-branch, and mixed configurations) would propagate in XLPE cable insulation. Three basic treeing propagation phases (initiation, stagnation, and rapid propagating phases) are presented in electrical tree propagating process. If initiation phase is very active, the single branch tree will propagate while if this phase is weak then the bush tree will occur more easily. There would be a clear double structure of electrical tree when it grows at submicroscopic structure uneven region of the material. A new parameter, the expansion coefficient is introduced to describe the electrical tree propagation characteristics. In addition, two other coefficients being used to describe our experimental results are dynamic fractal dimension and growth rate of electrical tree.