Rotor Winding Analysis for Superconducting Electrically Excited Synchronous Machines

The use of superconducting rotor windings in the electrically excited wound field synchronous machines can allow achieving enhanced power density and drastic weight reduction. Indeed, thanks to the large current carrying capabilities offered by the high-temperature superconductors, higher air gap fields can be produced compared to the conventional copper windings. However, the superconductors feature nonlinear performance depending on the transport current, applied magnetic field and operating temperature. In that respect, this paper investigates the resistance, inductance and total losses in steady-state of a high-temperature superconducting rotor winding for a wound field synchronous machine. The analysis is first performed at no-load to evaluate the impact on each superconducting tape of the self-generated field and of the magnetic field simultaneously produced by all the other tapes. Subsequently, the impact of the armature reaction on the resistance and total losses of the rotor superconducting winding is determined for different stator current vectors, causing additional flux lines to cross the tapes. The results of this analysis are useful for the design of the DC supply for the superconductors and of the rotor cooling system.