HTS POWER TRANSMISSION CABLES -- OVERVIEW

The major players in development of power transmission cables using high temperature superconductors are Pirelli and Southwire Corporation in the United States; Siemens, Pirelli, and BICC in Europe; and Sumitomo Electric Corporation, Furukawa, and Fujikura in Japan. Each of the major Japanese corporations manufactures its own HTS tapes. Siemens also manufactures its own HTS tapes, but it has also purchased material from others for use in earlier experiments. Pirelli has an arrangement with American Superconductor Corporation (ASC) that gives it exclusive access to ASC's tapes for use in power transmission cables. IGC also supplies high performance HTS tapes to this marketplace (Beales et al. 1996). All experimental and prototype HTS cables have been manufactured with multifilamentary tape containing the BSCCO-2223 compound.

The German government is providing half the funds (DM 20 million over three years) necessary to complete the cable program carried out and cost-shared by Siemens. In both the United States and Japan, on the other hand, the utilities are playing a major role in promoting the development of HTS cables. Tokyo Electric Power Company (TEPCO) provides nearly a million dollars annually to both Sumitomo and Furukawa to develop HTS cable prototypes and terminations, respectively. Chubu Electric Power Company has also worked with both Fujikura (Kume et al. 1995) and Sumitomo (Masuda et al. 1995) to develop related technology. In the United States, the Electric Power Research Institute, with some financial assistance from the Department of Energy, has invested heavily in power cable technology by forging a close alliance with Pirelli and ASC; total program costs are estimated to be $6 million over three years. Pirelli, Siemens, and BICC Cables have benefited from an earlier European collaboration, which included GEC, ABB, and Alcatel Cable, and which was financially supported by the European Commission under both the JOULE and BRITE-EuRAM initiatives.

The European project resulted in a very useful techno-economic study (Ashworth, Metra, and Slaughter 1993) that allowed individual members of the consortium to decide whether there was sufficient incentive to pursue further development of cable technology on their own. The significant conclusions of this study were (1) that for transmitted powers greater than 1 GVA, the HTS conductor's critical current density must exceed 200,000 A/cm² at liquid nitrogen temperatures in order for the overall costs to be comparable to conventional cables; and (2) that, in a 150 mm fixed diameter duct, an HTS cable can transmit up to seven times more power (to 700 MVA at 66 kV) at the same transmission cost.

HTS conductors, like so many other materials in their embryonic development phases, must exhibit improved performance and become less expensive if they are to gain widespread acceptance as articles of commerce. The Joule study presented a target performance-price window for HTS conductors (Fig. 3.1): for transmission of 400 MVA in a fixed diameter duct (believed to be an early application of HTS cables), the superconductor must carry in excess of 150,000 A/cm² if the price is about $40/meter. If the price falls to, say, $5/meter, the superconductor performance may be as low as 50,000 A/cm². For a given conductor price, say $5/meter, the "economic" critical current density is greater for application in a high power link than in a fixed diameter duct. This seems reasonable, as HTS must compete with the best available conventional cable solution in the former case, whereas HTS can be considered enabling in the latter.

Fig. 3.1. Performance-cost limits from a "break-even" analysis (1 ECU ~ $1.20).