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Open AccessConcept Paper

Superconducting AC Homopolar Machines for High-Speed Applications

Kalsi Green Power Systems; Princeton, NJ 08540, USA
Robinson Research Institute, Victoria University of Wellington, PO Box 33436, Lower Hutt 5046, New Zealand
Author to whom correspondence should be addressed.
Energies 2019, 12(1), 86;
Received: 5 October 2018 / Revised: 20 December 2018 / Accepted: 25 December 2018 / Published: 28 December 2018
(This article belongs to the Section Energy Storage and Application)
PDF [2982 KB, uploaded 28 December 2018]


This paper presents a novel high-speed alternating current (AC) homopolar motor/generator design using stationary ReBCO excitation windings. Compact, lightweight, high-efficiency motors and generators are sought for a multitude of applications. AC homopolar synchronous machines are an ideal choice for such applications as these machines enable very high rotational frequencies. These machines include both AC armature winding and direct current (DC) excitation winding within the stationary part of the machine. The stationary excitation winding magnetizes a solid steel rotor, enabling operating speeds limited only by the mechanical stress limit of the rotor steel. The operating speeds are many multiples of conventional power 50/60 Hz machines. Significant cooling requirements limit machines of this type utilizing copper excitation windings to only a few kilowatts. However, megawatt ratings become possible when superconductor coils are used. This paper describes the design and analysis of an AC homopolar machine in the context of developing a 500 kW flywheel system to be used for energy recovery and storage in commuter rail subway systems. Different approaches are discussed for an AC armature employing conventional copper coils. Challenges of building and cooling both armature and field coils are discussed and preferred approaches are suggested. Calculations of the machine performance are then made. View Full-Text
Keywords: superconducting machines; superconductors; high-speed machines; AC homopolar machines; energy storage; flywheel energy storage superconducting machines; superconductors; high-speed machines; AC homopolar machines; energy storage; flywheel energy storage

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Kalsi, S.; Hamilton, K.; Buckley, R.G.; Badcock, R.A. Superconducting AC Homopolar Machines for High-Speed Applications. Energies 2019, 12, 86.

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