Quench in High-Temperature Superconducting Motor Field Coils: Reduced-Temperature Modeling of HTS Tapes

The concept of reduced temperature for the characterization of the electrical properties of HTS tapes is presented. The formulation was developed based on experimental data from [1] and verified by experimental data from [2], [3]. Also, the experimental data from [4]-[6] indicate that the same formulation may be applicable to NbTi and Nb₃ Sn LTS superconductors. In general, the electric field in a superconductor is a function of four parameters: temperature, perpendicular and parallel magnetic flux densities and current. In the proposed formulation, the electric field is determined from only two parameters; the current and a quantity which we have chosen to call the reduced temperature. The latter is defined as the difference between the actual temperature and the critical temperature as determined by the perpendicular and parallel components of the magnetic flux density. This formulation results in considerable simplification in the application of the well-known power law for the DC electric field in HTS tapes. First, the characteristic current and the power exponent can be expressed as functions of the reduced temperature only. Second, the power exponent reduces to a function of the critical current alone.