AN APPROACH TO THE MODELING OF PARTIAL DISCHARGES IN ELECTRICAL TREES

A partial discharge model has been developed to simulate experimental partial discharge activity within electrical tree structures grown in polymeric based insulation. A pin plane electrode arrangement and tree were defined on a 41 x 44 grid representing an area 2 mm by 2.1 mm. A sinusoidal 50 Hz voltage was applied to the pin tip and 3600 time ste ps per cycle were used to give a phase resolution of 0.1 degrees. Part ial discharges were simulated at each time step by adding one or more dipoles of charge onto the tree structure to reduce the potential diff erence between adjacent points in the tree from V-on to V-off. Each di pole of charge represents a local electron avalanche occurring over a distance equal to the grid spacing. The model parameters, V-on and V-o ff, represent the discharge properties of the decomposition gas. Parti al discharge current pulses in the external circuit and the induced im age charge were calculated as a function of time. The spatial distribu tion of the emitted light in the tree structure over one cycle of the applied voltage was also calculated. The close agreement between the c alculated and experimental data suggests that the underlying assumptio ns used in the construction of the partial discharge model are appropr iate for the case of electrical trees grown in the flexible epoxy resi n.