Experimental and Numerical Studies of Thermoelastic Behavior of High Temperature Superconductors

Superconducting Fault Current Limiters (SFCL) are decisive solutions to limit faults in the electric grid. They make use of High Temperature Superconducting (HTS) tapes and operate at cryogenic temperatures. Such tapes are subjected to thermo-mechanical stresses due to 1) the mechanical constraint of the specific configuration of the SFCL and 2) the different thermal contractions of the tape and the other SFCL components. Experimental and theoretical studies aimed at estimating such stresses were developed and applied to a commercial HTS tape in test configurations at 77 K, based on strain gage methods and numerical simulations respectively. The results of both approaches agreed satisfactorily. The stresses ranged between 70 MPa to 85 MPa in linear test configurations and between 300MPa and 320 MPa in cylindrical ones, in both cases resulting well below the tape safety thresholds. A strain gage-based method was also set up and applied to measure the tape Coefficient of Thermal Expansion (CTE) at 77 K. It resulted close to that of the main metallic component of the tape. Such method is applicable to all the components of an SFCL.