Influence of impedance contrast on field distribution and tree growth in laminate dielectrics

The effect of the impedance characteristics of an imbedded barrier and inclusions on tree growth and field distribution characteristics was explored through Monte Carlo and finite element method based simulations. A stochastic tree propagation computer model was developed for the laminate composites that were comprised of a high-permittivity barrier layer imbedded in the low permittivity matrix. The impedance of the high-permittivity barrier was altered by systematically changing the permittivity (ε_r) of the barrier, resulting in a permittivity contrast ranging from 1 to 100. The model showed that there is a significant change in the various breakdown tree propagation characteristics such as number of breakdown steps, speed and shape with impedance contrast. A compilation of several simulation runs was statistically analyzed for each barrier and the number of breakdown steps increased significantly as the barrier permittivity approached 100. The results of this model can be generalized to impedance contrast between dielectric layers that include complex permittivity.