Partial discharge. III. Cavity-induced PD in solid dielectrics

For pt.II see ibid., vol.6, no.5, p.35 et seq. (1990). The question of how to relate the magnitude of the measured, effective, partial discharge (PD) to the size, shape, and position of the cavity within a solid dielectric system is addressed. The causes of cavities are examined, and a brief review of gas breakdown is given. It is then shown that for a range of geometries, such as parallel plate and coaxial, one can develop analytic solutions (i.e. formulas), and that for any system the solution can be found using computer-based methods for calculating the electric field throughout a sample. Scaling rules are derived from the physical model.<>