Characteristics of restricted ionization and its relation to voids in insulating materials

THE phenomena accompanying the formation of corona about cylindrical conductors and the laws governing such corona formation have been under investigation for a number of years, and the relations of such corona loss to voltage gradient, pressure, temperature, and the geometry of the system are now quite completely rationalized. Corona or ionization also occurs in restricted spaces, such as the voids which frequently are formed in dielectrics during their fabrication, and this corona formation has important effects on the behavior of such dielectrics. An example of such restricted corona formation is to be found in high-voltage impregnated-paper cables^1,2,3 within which occluded-gas spaces occur. Although the characteristics presented in this paper are for gaps longer than those ordinarily occurring in cables,^4,5,6 data obtained with cables show that the characteristics differ only quantitatively. The effect of such gaseous films on the deterioration of the insulation is well known. A knowledge of the characteristics of restricted ionization has made it possible to separate the solid-dielectric and the ionization losses in cables.^2,3