Superconducting lines for the transmission of large amounts of electrical power over great distances

As an application of high-field, high-current superconductors we sketch the design of a power transmission line to carry 100 GW (10
¹¹
watts) of direct current over a distance of 1000 km. (It is interesting to note that the present peak power generating capacity of the United States is approximately 200 GW, or just twice the capacity of the proposed line.) Such a line, in contrast to one made of ordinary metal, would dissipate none of the power transmitted through it, although it is necessary to tap power from the line for refrigeration. The consequences of negligible transmission loss are substantial: power transmission would be more economical than the present practice of shipping coal to the region in which electricity is generated and consumed; generating-plant site selection could be made almost entirely on economic considerations; at the same time, thermal and air-pollution problems could be minimized; novel power sources could be considered. The power line would be made of Nb
3
Sn and would be refrigerated to 4°K. The power must be transmitted as direct current, rather than as alternating current, because the very large (comparatively) alternating-current losses would require excessive refrigeration capacity. Specifically, we shall discuss a line at 200 kV carrying 0.5 × 10
⁶
A. The investment in the line will be approximately $806 million, or $8.06/kW. Of this, some $6.06/kW is line cost, the remainder being converter cost, which, of course, is the same for an ordinary dc line. In comparison with the shipping of coal, the investment cost would be repaid in ten months. We have investigated in some detail the problems of refrigeration along the line, including those of heat leak through the wires which deliver power to customers at room temperature. The efficiency of the line is greater than 99.9 percent (power transmitted less the power drawn off to run refrigeration equipment, all divided by transmitted power). While the technical discussion is probably correct, the cost figures do not include engineering expeditures and do not consider in detail the costs involved in providing the redundancy and safety factors for, say, a failure rate of one per ten years with a time of a few seconds to restore power. This is not an engineering study but rather a preliminary exploration of feasibility. Provided satisfactory superconducting cable of the nature described can be developed, the use of superconducting lines for power transmission appears feasible. Whether it is necessary or desirable is another matter entirely.