Cost analysis of dielectric systems for ac superconducting power transmission line

The EEl sponsored Linde study of ac superconducting power transmission lines dealt primarily with a pressurized helium dielectric system having an average electric stress of 200 kV /cm at the specified impulse voltage rating of the line. In this paper I have explored the effect on the overall system economics of varying the maximum allowed dielectric stress through the use of pressurized helium, vacuum or a solid dielectric. While a number of approximations have been made in the course of deriving the relation used to produce the curves shown in Figure 4, the following general conclusions can still be drawn from these results. First, for a reasonable choice of dielectric parameters the increase or decrease in the total system cost from that calculated for the pressurized helium system with EB = 200 kV / cm would generally be less than 15%. Second, for a given value of EB the solid dielectric system will be more expensive than a pressurized helium or vacuum dielectric system. Third, the cost of both the vacuum and pressurized helium dielectric systems decrease monotonically as the value of EB is increased. Fourth, for the solid dielectric system the cost initially decreases as EB is increased, reflecting the decrease in solid dielectric volume and hence dielectric cost, as well as the cost decreases arising from the decrease in size and cost of both the cryogenic envelope and its associated refrigeration requirements. Eventually, however, at high values of EB, the cost will increase with increasing EB, reflecting the increasing cost of the refrigeration needed to overcome the increase in dielectric loss as EB and, hence, the line capacitance increases.