Tree-inception in PMMA with a barrier

The experimental results of a study of the tree-inception phenomenon for three-layer dielectrics in a divergent field are presented in this paper. It is shown that the tree-inception time depends on both the position of the high-permittivity barrier in the insulating gap and the ratio of the permittivities of the barrier material and main dielectric, and that it has a maximum at the optimal barrier position. It is found that the tree-inception length has a minimum value at this barrier position. Good agreement between the coefficient of the local field non-uniformity and the tree-inception time or the initial tree length was found.