On the intrinsic space-charge in a d.c. power cable

In a d.c. power cable in operation, the temperature, and hence the conductivity σ of the insulation, increases from sheath to core. Combined with the local field, this radial conductivity gradient builds up an “intrinsic space-charge. In his treatment of charge buildup, Lau (1970) considered the temperature dependence of σ but not its field dependence. Here, this topic is revisited using the mean radius r¯ and the reduced field, ratio of the actual field over the field without space-charge. By comparing the predictions with the field distribution measured by the techniques now available, the “extrinsic” injected charges, important for the cable life, should become distinguishable