The influence of cavity shape and sample geometry on partial discharge behavior

Analytical expressions are developed for the apparent charge and the energy dissipation of partial discharges (PD). Both are dependent upon the volume and shape of the cavity. Contrary to the energy dissipation, the apparent charge also depends on the insulation thickness, sample geometry and position of the cavity in the sample. The apparent charge is proportional to the relative permittivity of the dielectric which has little or no effect on energy dissipation in disk-shaped or nearly spherical cavities. Based on these findings it appears that the discharge energy is an appropriate measurable quantity to characterize PD inside the dielectric.