A theoretical study of extruded, graded dielectric cables

Power cables designed for 115-KV and above require a relatively thick insulating wall that results in a large overall cable diameter and a large volume of insulation per foot of conductor, A typical 138-KV cable may be made with an insulating wall of nearly one inch. The radial electric stress in this insulation is a maximum at the strand shield-insulation interface and decreases (inversely with radius) to the insulation-insulation shield interface. By using two or more dielectric layers with different dielectric constants one can reduce the maximum electric stress near the strand shield.