Design of a single-phase 6.5 MVA/25 kV superconducting traction transformer for the Chinese Fuxing high-speed train

•6.5 MVA HTS traction transformer systems can be employed in Chinese Fuxing trains.•Roebel cable in the LV windings for large current and minimal AC loss.•Winding length ≥ 1 m, high quality wires, and flux diverters gives AC loss < 2 kW.•Open-loop cooling system with sub-cooler can be integrated inside the cryostat.•A nominal efficiency of 99.5% can be achieved for HTS transformer system.