Estimating driving-force of electrical deterioration of insulators based on energy-release rate.

Detailed analyses of mechanisms of electrical treeing phenomenon have been carried out yet. In this study, we analyze electrical trees as very thin 3D tubes between a treeing needle and a plate electrode and calculate the energy-release rate to estimate and evaluate the driving force required for crack propagation. This study implements a new method applying an analogy between concepts of fracture mechanics and Maxwell stress to calculate the energy-release rate in a 3D model. As a result, we obtained the energy-release rate around a volume near the needle-electrode and electrical trees. In addition, path independence is verified, and it is found to be conserved only when the path does not include the interface between the needle-electrode and the insulation material. Then, the values of energy-release rate obtained in each condition of tree length and applied voltage were compared, respectively. It is revealed that the 1D-growth of the tree has a small effect on the value of the energy-release rate, and that the value is proportional to the square of applied voltage on the needle-electrode. These results imply that calculating energy- release rate exhibits a potential to mathematically evaluate the growth of electrical trees, connecting its results to experimental results such as partial discharge phenomenon and/or space charge accumulation. [ABSTRACT FROM AUTHOR]