Impact of presence of water tree and microcavities on the electric field distribution in XLPE insulation

The aim of this work is to investigate the influence of presence of water and air cavities close to the front of vented water tree growing from interior of semiconducting layer of power cable on the electric field distribution. For the determination of the electric field, a numerical method has been used under Comsol Multiphysics environment. This paper shows that, the presence of water tree induce a significant variation of electric field in the insulation. The electric field is amplified at the periphery of the water tree and in front of it; this effect is further enhanced if natural or created defects are present in the polymer in front of the water tree zone. The distribution of field may scarcely be affected by the number and the size of the micro-cavities, as well as the distance between water tree and these cavities. The increased enhancement of the field due to the presence of cavities of small diameters in regions either near the vented water tree can leads to the appearance of local electric fields higher than partial discharge inceptions and electrical treeing. Moreover, the initiation of electric tree is more probable in the case of water cavities than in the case of air cavities. The mutual interaction between cavities contributes much more to this apparition.