Evaluation of superconductors for large scale switching of electrical power

The extreme difference between the electrical resistance of a superconductor in the superconducting and the normal state suggests its application in various large scale switching operations of electrical power. We have performed a theoretical evaluation of such applications in a superconducting rectifier operating at 60 Hz both for magnetic and thermal switching. Operation in both liquid helium and hydrogen has been considered. Based on an optimistic evaluation of the materials parameters expected to become available, neither mode of operation appears feasible. For magnetic switching the difficulty arises mainly from the large magnitude of the switching losses. This requires operation using a relatively low critical field, which is incompatible with the high normal resistivity needed in an efficient switch. Thermal switching at 60 Hz appears infeasible because of the incompatibility of a fast thermal time constant and a reasonably large temperature increment above the temperature of the liquid coolant. These problems are absent in devices operating at frequencies much less than 60 Hz, and various potential applications will be discussed.