Alternating Current (AC) Losses Associated with High Temperature Superconductors

Because on their high current carrying capacity in large magnetic fields, biaxially oriented superconducting films (coated superconductors) are the only superconducting materials that offer the possibility of operating in power applications at liquid-nitrogen temperatures in AC fields. Their use is predicated on the assumption that ac losses in these materials can be reduced to a very low level. To do so requires the use of innovative conductor geometries. Present superconductor loss theory is inadequate for predicting the loss in coated superconductors with these geometries under realistic conditions found in generators and transformers. New loss theory is required. This Phase I program will develop new ac loss models for coated superconductors. The program will: (a) extend ac loss theory to apply to coated conductors, (b) develop practical conductor geometries which minimize ac losses under conditions which exist in generators and transformers, (c) investigate generator and transformer designs which best take advantage of coated conductors, and (d) prepare a test plan for a Phase II demonstration of loss prediction and conductor performance in a short sample of YBCO and in a USAF generator presently under construction. The advanced ac loss models developed in this Phase I program and the novel new HTS coated superconductor geometries developed to minimize the combined transport current and applied magnetic field losses in these new conductors will allow us to determine if coated conductors can function at high temperatures in emerging AC hardware. The development of these analytical models and conductor geometries will be essential to the successful application of these HTS conductors to the lightweight generators and transformers that are needed for military (and ultimately commercial) applications of superconducting hardware.