Optimization of 1 MVA high TC superconducting transformer windings

It is common practice to wind coils in pancake shape for conventional high voltage transformers because of electrical insulation problems. In HTS superconducting transformers, the perpendicular component of magnetic flux density (B_r) applied to HTS tapes of pancake windings becomes larger than that of solenoid winding, thereby decreasing the critical current in the HTS tapes. This paper introduces several methods to reduce B_r applied to the HTS tapes in the transformer with double pancake windings by changing winding arrangements and the relative permeability of flux diverters. We have conducted a winding design for a single-phase 1 MVA 22.9 kV/6.6 kV HTS transformer. The magnetic field in the spaces occupied by the windings and its vicinity was numerically simulated. We observed a change of B_r due to various gap arrangements of high voltage and low voltage windings and various reciprocal arrangements. We also observed a change of B_r on the HTS tapes due to variation of relative permeability of flux diverters placed between the high voltage winding and the low voltage winding.