Shaping of Filamentary Streamers by the Ambient Field
H A. Fowler, J E. Devaney, John G. Hagedorn
We have simulated the fast streamer stage of liquid dielectric breakdown as stochastic growth of a branching fractal tree. Breakdown and threshold properties of the fluid are represented in the random filter procedure. A range of fractal densities, from sparse to bushy, is approximated by the choice of power-law (cube to linear). The choice of threshold (cutoff) voltage also significantly affects the growth form. These parameters combine with the shape and concentration of the electric field, to regulate the distribution and directedness of the local discharge growth pattern. A large grid (128 cubed) is used for the discretization. Diagonal growth paths to neighbor-vertices are included, increasing the choice of available directions for each discharge event. We use a combination of data-parallel programming and three-dimensional visualization. Complete growth histories, evolving from the voltage distribution, can be displayed in animation or in color banding against the trials variable, which simulates a time tick. Side views of structures provide comparison against sub-microsecond snapshots from experiment. Results include sparse, directed trees evolving from a cube-law filter; also dense trees from a linear filter, whose consical upper-envelope boundary is strongly influenced by the choice of threshold (cut-off) potential.
1999 Annual Report, Conference on Electrical Insulation and Dielectric
October 17-20, 1999
Conference on Electrical Insulation and Dielectric Phenomena