For power engineering applications, the HT Superconductors need to have current densities (j) in the superconducting core of a wire or tape of up to 10{sup}5 Acm{sup}(-2), in magnetic fields (H) of up to 10 Tesla. At present, these j-H characteristics only appear to be attainable with BSCCO materials at temperatures significantly below 77K. Between about 30K and 80K, the j-H characteristics decrease monotonically with increasing temperature, due to thermal deactivation of the flux pinning centres and {OX flow effects. At temperatures above about 70K, the current densities in BSCCO 2223 tapes decrease rapidly with applied field, and therefore the use of liquid nitrogen as a refrigerant at 77K and 1 bar is not a viable option at present. There are indications however that YBCO materials offer satisfactory performance with high current densities at liquid nitrogen temperatures; but the production of long lengths of high current 10-100A tapes or wires is proving difficult. At present, therefore, power engineering applications require temperatures below 65K, possibly down to 50K or even 30K.
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