Cryogenic Cooling of Motor Armature Windings for Aircraft Applications

Electric machines for mobile and transport applications are under intensive development at present. In order to successfully electrify transport and mobile applications, high power, lightweight motors and generators are required. Pushing machine performance above 20kW/kg or 30kW/kg requires a step change in air-gap field and hence current density. Superconducting windings show great promise for application to the DC field winding of Synchronous AC machines, where the high currents and low thermal loads allow for high magnetic fields. However, the armature windings present a greater challenge. Even superconductors suffer loss mechanisms under AC currents and in AC magnetic fields, producing kilowatts of heating in MW-scale machines. This heating load at cryogenic temperatures of 20-40K presents a significant thermodynamic and materials challenge. This paper will present a number of different armature options for MW-scale electric machines. We will consider superconductor armatures in MgB2, CORC and Roebel cables made of REBCO, as well as cryogenically cooled nonsuperconductor armatures made with aluminum Litz wire.