The interest in applying superconductivity (SC) to electric power and energy storage applications is directly related to expectations for improved performance and efficiency advantages over conventional room-temperature devices. Use of superconducting wire or tape in power generators or large magnets, for example, provides the ability to transport large dc currents with no measurable resistive losses. High magnetic fields can thus be produced at a significantly reduced cost for the energy required for operation. This economic advantage is also driven by a simple caveat that the superconductor should provide the ability to generate sufficient amp-turns within a specific volume. A practical superconductor must thus have a current density, at high magnetic fields, in excess of ordinary copper in order to be technologically useful. The early so-called "low temperature" superconductors (LTS) that operated in liquid helium easily satisfied this requirement and as a result spurred the development of many prototypes for generators, motors, transmission lines, and energy storage magnets. All of these demonstrations were compromised by the costly and technologically complicated requirement for liquid helium; consequently, they were not easily accepted by utilities or end-users, especially in the United States.
The 1986 discovery of high temperature superconductors (HTS) excited the scientific community and provided new impetus for pursuing superconducting electric power applications because of the prospect for higher temperature operation at liquid nitrogen (77 K) temperatures or above. It is fair to say that this HTS discovery would have been of little importance if the earlier work of Shubnikov and Abrikosov in the Soviet Union had not recognized that certain superconducting alloys identified as Type II superconductors had the ability to carry high transport currents in technologically useful magnetic fields (Larbalestier 1990, 1027).
It was eventually determined that highly cold-worked alloys, such as Nb-Ti and Nb-Zr, contain a wide range of defects, impurities, and precipitates that act as "pinning centers" limiting the movement of flux, which results in a highly hysteretic magnetization and the ability to carry high transport currents at high magnetic fields. These materials with high pinning and outstanding transport properties, referred to as "hard" superconductors or "dirty" Type II materials, have been rapidly developed to provide fairly cost-effective wires or tapes with acceptable mechanical properties (Berlincourt 1987).