Numerical solution of space charge distribution in high field dielectrics

Electrical insulation often fails as a result of defect-induced highly inhomogeneous electric fields and the high field phenomena induced thereby. An understanding of what goes on in the microscopic high field region surrounding a small defect is therefore of great interest. Experimental investigation is made difficult by the small size of the high field region, typically just a few μm. The region cannot be made larger for experimental purposes, as the power densities involved in the high field phenomena would cause thermal runaway if dissipated throughout a larger volume. The difference between impulse and dc electric strength, the influence of prestressing and impulse risetime on breakdown voltages, and the polarity dependence of breakdown voltage in needle-plane geometry have all been explained by invoking high field-induced space charge. The present contribution therefore focuses on the computation of such space charge in a two-dimensional system