An AC Homopolar motor recently built at Robinson Research Institute demonstrates high operating speeds, wireless energisation of HTS coils, and a novel hybrid laminated steel stator.
AC Homopolar motors magnetise a solid steel rotor using a non-rotating superconducting field coil rigidly mounted to the stator. As the field coils do not rotate with the rotor, cryogenic cooling and electric current can be supplied without rotating couplings. This architecture enables high speed operation, and large-scale AC Homopolar motors are expected to achieve over 12 kW/kg as required for aircraft powertrain applications.
The 10 kW AC Homopolar motor built at Robinson Research Institute is designed for 30,000 RPM operation, 16,000 RPM faster than any previously demonstrated superconducting motor. This motor is designed as a modular testbed for superconducting technologies, and can be partially disassembled to facilitate modification or replacement of all superconducting components without the need for reengineering of the rotor.
Engineering work towards manufacture of this motor revealed the fully laminated stator described in previous work is not required, as much of the stator experiences non-alternating magnetic flux only. The built motor features a hybrid stator that includes low loss solid steel regions alongside conventional laminated steel stacks.
Current supply to the 200 A ReBCO field coil is supplied by a conventional DC source, but a variable speed HTS Dynamo is also included to demonstrate wireless energisation of closed superconducting circuits. The HTS Dynamo is designed to provide continuous and controllable superconducting circuit current without the large cryogenic load that results from current supply via copper leads.
In this presentation we will describe the operating principle of the AC Homopolar motor, including the revised understanding of the magnetic behaviour as developed through 3D finite element modelling techniques. We will also detail the manufactured motor design, including the unique features that enable this motor to be used as a testbed for a variety of superconducting motor technologies developed at Robinson Research Institute.

Keywords: Synchronous Motor, Hybrid Motor, Partial Superconducting Motor, Wireless Energisation