Prospect of employing conductors at low temperature in power cables and in power transformers

An estimate is made in economic terms of power that could be saved if the conductor in a 760MVA, 275kV a.c. cable were alternatively: niobium at 4°K aluminium at 20° K beryllium at 77° K The first of these metals is a soft superconductor, and the others, if sufficiently pure, are assumed to exhibit resistivities of 3×10¿9 and 2×10¿8¿cm, respectively. The analysis takes into account the effects of eddy currents at these resistivities, and considers the spacing of refrigerating units along the cable and the distribution of refrigerants in order to minimise that part of the cost that stems from refrigeration. The study turns next to a 570 MVA generator transformer with aluminium at 20°K and resistivity 3×10¿9¿cm, or, alternatively, a hypothetical metal at 77°K and resistivity 2×10¿8¿cm, as the winding conductor. The paper finds that these metals would both have to be used in the form of foil, and derives expressions for three components of foil loss. It then compares the possible saving in conductor loss with the drive power used by the refrigerators, and with the cost of refrigeration plant. It finds that neither in power transmission by cable, nor in power-transformer windings, is there any promise of a net saving over conventional costs that would warrant the constructional and operational complexities entailed in deep refrigeration.