Analysis of electromagnetic characteristics of 6.5 MVA/25 kV HTS traction transformer using T-A formulation

Low AC loss of the winding of high-capacity high temperature superconducting (HTS) traction transformer is a very important link to introduce large capacity traction transformer into commercialization. A new winding structure is proposed for the transformer. The HV windings are made of double pancake coils (DPCs), which are wound by 4.8 mm-wide tapes, and the LV windings, which are wound by 12 mm-wide tapes, are solenoid coils. The electromagnetic characteristics of the new winding structure of the traction transformer are analyzed by H-formulation homogenization method and T-A formulation homogenization method respectively. Significant HTS tape cost reduction could be achieved without compromising AC loss by using hybrid windings into the new winding structure. We report that the H-formulation homogenization model and T-A formulation homogenization model are used to calculate the AC loss of the new winding structure with flux diverters (FDs) at the end. The results meet the design requirements of less than 2 kW, which shows the feasibility of the new winding structure. Due to the good convergence of H-formulation and poor convergence of T-A formulation under the homogenization model of the transformer, no one has used T-A formulation to calculate the electromagnetic characteristics of the transformer before. Due to the simplicity of T-A formulation applied to large-scale superconducting system, a new form of mesh generation is proposed to improve the convergence and accuracy of T-A formulation homogenization model calculation of the transformer in this paper. This paper verifies the correctness of the calculation of HTS transformer by T-A formulation, and provides a reference for the application of T-A formulation in more superconducting fields.