A Numerical Method for Calculating and Optimizing the Coupling Factor of HTS Air-Core Transformer

The coupling factor is a crucial parameter for a high-temperature superconductor (HTS) air-core transformer. This paper proposes a numerical method for calculating and optimizing the coupling factor, which took the influence of insulation distance into account. To verify this method, a laboratory-scale HTS air-core transformer was fabricated and tested in liquid nitrogen. GdBCO HTS tapes were used for HTS windings. The primary windings were six single pancakes (SPs) in series, and the secondary windings were three SPs in parallel. Each SP has 32 turns. The numerical calculation and the experimental measurement were consistent. Because the HTS air-core transformer has no specific path for the magnetic flux compared with the full-core transformer, more attention should be given to optimizing the coupling factor. The relationship between the windings arrangement, the insulation distance, the radial dimension, and the coupling factor was discussed by the numerical calculation method. The conclusion of this paper will guide the design of the 1-MVA/10-kV/400-V HTS power transformer, which is going to be built later this year.