The homogeneity of electric fields also contributes to the
dielectric strength of insulating materials. The dielectric
strength characteristics of porcelain and glass in homogeneous
and inhomogeneous fields are presented in Fig. 1. The figure
shows that the dielectric strength of porcelain is not affected by
the homogeneity of electrical field (Fig. 1, lines 2 and 3) as
much as the dielectric strength of glass (Fig. 1, lines 1 and 4).
As nonuniform fields require a lower value of voltage for
breakdown to occur at any distance between electrodes, the
main task while designing an insulator is to keep the shape of
the electric field in the insulator as homogeneous as possible,
especially when the insulator is subjected to exceptionally
strong electric fields, as in case of lightning strikes.