Abstract
Expressions are derived for the inception voltage at which discharges occur in gaseous voids entrained within the insulation of single and three-core, screened as well as belted, power cables. The inception voltage V sub(i) depends upon the conductor diameter, the insulation thickness, the dielectric permittivity, the location, shape and length L of the void as well as the pressure P of the gas inside the void. It is shown that for a given cavity, V sub(i) depends upon the product PL as well as P. For a cavity of known shape, size, and location, a minimum voltage V sub(min) exists below which partial discharges do not occur. V sub(min) decreases with increasing void size and is lower for cylindrical voids when compared to the spherical ones.