Chapter 3: AC Losses in Superconducting Fault Current Limiters

In spite of having zero electrical resistance, superconductors exhibit dissipation in AC transport. We show that the physical origin of this phenomenon is intimately linked with the ability to carry large electrical currents, and critically depends on the way in which the magnetic field interacts with the superconducting material. Therefore, the AC loss is not a property of material itself, but can be significantly influenced by the configuration of conductors in a superconducting device. From the variety of arrangements in which the AC loss has been investigated, those that are most relevant for the design of superconducting fault current limiters (SFCLS) are discussed: AC transport by a single wire and by a bifilarly wound coil. Basic engineering formulas are presented allowing the reader not familiar with the issue to obtain the first guess for the expected AC loss level.