Simulation of partial discharges and electrical tree growth in solid insulation under ac voltage

An off-lattice three-dimensional stochastic-deterministic model of electrical tree growth in solid insulation and of the partial discharges within the tree has been developed. The electrical tree growth is described by a stochastic propagation of the channel structure in the insulator. The channel growth is driven by the electric field and an irreversible damage accumulation in the insulation. The damage accumulation is considered to be a local process in the dielectric material surrounding the tree channels. The rate of the damage accumulation is proportional to the energy release within the channels. The charge redistribution results from the partial discharge inside the electrical tree. The partial discharge starts, when the electric field along the channels exceeds a specified inception value and stops, when the field falls below the threshold quenching value. The model has been used for computer simulations of partial discharge and tree growth under sinusoidal and triangular voltage in the needle-plane geometry. Phase-resolved and time-sequence patterns of partial discharges for different forms of electrical trees at different stages of their growth have been obtained. The simulation results have been compared with experimental data.