Reduction of insulation thickness and AC loss in a superconducting cable under lightning-surge-free circumstances

When a large amount of electric power is directly supplied through superconducting power cables from a satellite power plant to a future computer-based city center, they can be operated under lightning-surge-free circumstances. The insulation thickness necessary to withstand a lightning surge is left out of the consideration of such a condition. The authors point out that the reduction of insulation thickness is very effective in helping decrease not only the AC loss, but also the total transmission loss in the superconducting cable. Quantitative investigations are carried out with respect to a liquid-nitrogen-cooled high-T_c superconducting cable. A reduction of 20-30% of the insulation thickness is shown to result in a decrease of 15% of the total loss for a 3000-MVA, 275-kV cable. For a transmission capacity of 5000 MVA the reduction rate of the total transmission loss of a 275-kV superconducting cable is 35%