AC Losses in Superconducting Coils

Abstract

AC Supercoducting wire is being developed for electrical equipment such as superconducting transformers and superconducting generators. AC loss reduction is of primary concern in the development of such high-efficiency equipment. In reducing AC losses, it is necessary to develop assessment methods for AC loss in test samples which have shapes similar to the end-product equipment.
This paper describes a least squares calculation of AC losses of superconducting wire as a function of frequency and magnetic field strength measured in test coils.
Two sample solenoid coils were made to test the influence of different capacities and winding methods on AC losses in AC superconducting coils with rated capacities of 500kVA and 20kVA, and impregnated (epoxy resin) and non-impregnated windings.
The AC losses in the superconducting coils were measured by a calorimetric method using the evaporating rates of liquid helium. Estimated AC losses in the superconducting wire of the two coils were compared with joule losses of copper conductors at ambient temperature. As a result of this comparison, a low-loss AC superconducting wire winding can be made for electrical equipment rather than using conventional copper winding when used under low magnetic fields under 0.5 T.