ASSESSMENT STUDY OF SUPERCONDUCTING FAULT-CURRENT LIMITERS OPERATING AT 77-K

The possible impact of nitrogen-cooled superconductors on the design a nd cost of superconducting fault-current limiters is assessed by consi dering the technical specifications such devices must meet and by comp aring material properties of 77-K and 4-K superconductors. The main ad vantage of operating superconductors at 77 K is that the refrigeration operating cost is reduced by a factor of up to 25, and the refrigerat ion capital cost is reduced by a factor of up to 10. The heat capacity at 77 K is several orders of magnitude larger than at 4 K. This pheno menon increases conductor stability against flux jumps but makes switc hing from the superconducting to normal state slow and difficult. Cons equently, a high critical current density, probably at least 10(5) A/c m2, is required.