A Concept for the Intrinsic Dielectric Strength of Electrical Insulation Materials

There are analytical solutions of Laplace's Field equation which can be used to calculate the maximum potential gradient EMAX on an electrode surface as a function of voltage difference V, separation t, and radius R. Such solutions can be series-expanded and, after combining the first two terms of the series algebraically, they yield the general expression V/t= EMAXan (t+a)-n, where (V/t)= VA is the average voltage across the separation t, and a is a term involving radius of curvature only. If K is defined as EMAXan , then the expression becomes VA=K(t+a)-n which is strikingly similar to the expression VA= K(t)-n, an historically observed data correlation between VA and t, if a is ignored. The experimental observation that VA decreases with increasing t has been interpreted as a material property. However, the similarity with the series expression suggests that, at constant EMAX, this is a manifestation of the thickness-dependence of the spatial distribution of the electric field. If true, then voltage breakdown of an insulation material is occurring whenever a critical but constant value of the potential gradient EMAX is reached or exceeded on an electrode surface. It is suggested that this critical value of EMAX may be the intrinsic dielectric strength of an insulation material, herein designated as S.