Propagation and partial discharge characteristics of electrical trees in 110 kV XLPE cable insulation at power frequency applied voltage

Based on the combined methods of real-time microscope digital imaging technology and partial discharge (PD) continuous measurement, we studied the electrical tree structure properties, propagation law and PD characteristics in 110 kV XLPE power cable insulation at different power frequency applied voltages by the conventional needle-plane electrodes structure. The experimental results showed that trees at 9 kV displayed the features of diversity, namely, stagnation-type tree, branch tree and branch-pine tree, and the initiation and propagation time of stagnation-type tree were the longest, during the stage of stagnation, the PD erosion effect was remarkable. The initial time of branch tree and branch-pine tree at 9 kV was comparable, the propagation time of branch tree was short, and PD at stagnation stage was stable. During the stagnation stage, the PD of branch-pine tree was weakened; meanwhile, the pine structure occurred and grew rapidly. The trees at 11 kVrms, 13 kV, and 15 kV were branch tree and bush tree, respectively. The initial time of branch tree was long, but its propagation time was the shortest, and the PD effect for the tree growth was obvious. The initial time of bush tree was short. We calculated the fractal dimension of electrical trees by the box-counting method, according to the discharge-avalanche model theory, it was found that with the increase of applied voltages, the bush part of tree was more dense, the fractal dimension of electrical tree was increased, the damage of tree for insulation was expanded, the PD effect was weakened, and the propagation time of electrical tree was extended.