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, 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 at the end. The results meet the design requirements of less than 2 kW, which show 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 article. This article 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