Propagation of electrical tree growth in a composite solid insulation consisted of epoxy resin and mica sheets: Simulation with the aid of Cellular Automata

Electrical treeing is one of the principal factors affecting the insulating capability of solid insulation. Epoxy resin with mica sheets is used in machine insulation. In the present paper, a point-plane electrode arrangement was used in order to simulate the electrical tree propagation in such an insulating system. The mica sheets investigated were of comparable thickness with the epoxy resin. The simulation was performed with the aid of Cellular Automata (CA). Laplace equation has been solved setting appropriate boundary conditions at the interfaces between epoxy resin - mica sheet and epoxy resin - electrodes. The simulations were based on the local field variation, the local dielectric strength and also on the variation (even slight) of the dielectric constant of the insulating materials. Such local variations of the dielectric constants render possible local variations of the electrical field and, consequently, of the tree propagation. Mica sheets as barriers inside the main insulating material preventing the electrical tree growth. The thickness of mica sheets plays an important role in the propagation of trees. The simulations indicate that even in the case of a partial penetration of the mica sheets, no complete breakdown results. The applied voltage level plays also a crucial role in the resulting type of electrical tree. Higher applied voltages result in a bush-type tree, whereas lower applied voltages result in more pointed trees. The simulation results agree with experimental data.