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Lightweight ironless-stator PM generators for direct-drive wind turbines

Spooner, E.; Gordon, P.; Bumby, J.R.; French, C.D.


E. Spooner

P. Gordon

J.R. Bumby

C.D. French


A permanent-magnet electrical machine that employs lightweight spoked structures for both rotor and stator is described. The stator is ironless so that there is no direct magnetic attraction between rotor and stator. The lightweight structures are sufficient to carry the small forces due to the interaction of the permanent magnet field with the stator winding current. Despite the absence of stator iron and a large airgap, rare-earth magnets are able to create a working flux density of about 0.25 T at the winding. This is sufficient for an effective generator design because the lightweight structures offer the opportunity to build generators of unprecedented diameter. The outcome is a generator that has a mass typically 20–30% of equivalent designs based on iron-cored magnetic circuits, and with efficiency greater than 90%.


Spooner, E., Gordon, P., Bumby, J., & French, C. (2005). Lightweight ironless-stator PM generators for direct-drive wind turbines. IEE proceedings. Electric power applications, 152(1), 17-26.

Journal Article Type Article
Publication Date 2005-01
Deposit Date Apr 23, 2008
Journal IEE proceedings. Electric power applications.
Print ISSN 1350-2352
Electronic ISSN 1359-7043
Publisher IET
Peer Reviewed Peer Reviewed
Volume 152
Issue 1
Pages 17-26
Keywords Permanent magnet generators.