A Discussion on recent advances in heavy electrical plant - Superconducting cables for a.c. and d.c. power transmission

Abstract

The growth of electricity demand has led to a steady increase in the power-carrying capacity of underground power transmission lines. Some present cables are water cooled to increase their current rating, and further increases could be achieved by refrigerating the conductors to reduce their resistivity. The ultimate and best use of refrigeration is to cool to a few Kelvins above absolute zero so that superconductors can be used. The technical problems of both a.c. and d.c. superconducting cables are described, with particular attention to the choice of superconductor and the choice of dielectric. The conductor choice is heavily influenced by fault current requirements. Some possible cable designs are then discussed, and present progress towards such designs briefly summarized. The electrical parameters of superconducting cables are deduced, and tentative economic assessments put forward. For high-power levels, exceeding 2 GVA, superconducting cables may offer real advantages; on the other hand, it may be 20 years before substantial requirements for such cable will arise.