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Lookup NU author(s): Dr Rafal Wrobel, Dr Zaynah Ahmad
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© 2015 IEEE.High-specific-power electrical machines for transportation applications require effective thermal management to enable elevated power density and efficiency. Hollow-conductor windings offer direct internal cooling, reducing temperature rise and increasing allowable current density. This paper investigates the thermal performance of copper hollow-conductor windings fabricated using additive manufacturing (AM) and evaluated via reduced-complexity motorette demonstrators. The windings were produced using a filament-copper AM process, enabling continuous hollow channels along the full conductor length. Experiments demonstrate winding-to-coolant heat transfer exceeding 2000 W/m2K, corresponding to a 0.7l/min corresponding to a 37 × increase in allowable winding power loss relative to a baseline design employing conventional round copper conductors with liquid-cooled housing. Complementary theoretical analysis of complete machine variants shows that hollow-conductor cooling can significantly enhance machine operating envelope and efficiency, extending high-efficiency regions and torque-speed capability. The findings illustrate that direct cooling of hollow-conductor windings, enabled by AM, provides a viable route to higher specific output and improved thermal robustness in propulsion-relevant electrical machines. Practical considerations for integrating hollow-conductor windings into full machine assemblies are also discussed, including manufacturing, assembly, and thermal design implications.
Author(s): Wrobel R, Ahmad Z
Publication type: Article
Publication status: Published
Journal: IEEE Transactions on Transportation Electrification
Year: 2026
Pages: epub ahead of print
Online publication date: 15/06/2026
Acceptance date: 02/04/2026
ISSN (electronic): 2332-7782
Publisher: Institute of Electrical and Electronics Engineers Inc.
URL: https://doi.org/10.1109/TTE.2026.3703538
DOI: 10.1109/TTE.2026.3703538
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