Dr Antony Anderson C.Eng FIEE

Helical Windings in Electrical Machines

Helical windings are not new and found limited favour for dynamos in Germany in the late 1880s.[Fritsche] Today they are widely used for small d.c. machines of the ironless type, where they offer the advantage of low inertia and smooth torque at low speeds. They have also been used for linear motors [Eastham & Laithwaite] and transverse flux tubular motors [Eastham & Alwash]. The use in large a.c. machines was first proposed by Ross, Anderson and Macnab of the International Research and Development Company Ltd, who suggested it as a suitable armature for superconducting a.c. generators [UK patent 1975] and this was followed up by a detailed theoretical analysis [Anderson, Bumby and Hassall] published in 1980. A 4 MVA helical armature winding was used by Watnabe et al. as the armature winding for use in either a slotless or a superconducting generator. Conley et al. used a helical winding in an experimental 10 MVA superconducting generator at MIT in the late 1970s.

Relationship of helical to conventional lap and diamond windings

Helical armature for a small DC motor

Explanation of the helical winding

Unlike the conventional winding, the helical winding has no distinct division into active and end regions, because each conductor follows a helical path of constant pitch and diameter from one end of the machine to the other. In the conventional winding, each conductor follows an axial path in the active region and only has a circumferential component to its path in the end regions.

To understand how a helical winding works, consider the winding length of a diamond lap winding shown in the adjacent figure (a) to be progressively reduced as (b), by eliminating the so-called central "active" region and allowing the two diamond end windings to coalesce and form a semi-helical winding (c). The true helical winding (d) evolves from the wave wound diamond winding (d).

One phase of a two pole helical winding is shown above. Each phase consists of two parallel-connected helical loops, each of which is termed a phase group. Each phase group comprises one right-hand (inner) helical phase band connected in series with a returning left-hand (outer) helical phase band; a right hand phase band being defined as that which traces a right hand screw.

Notes on helical windings

FRITSCHE	British Patent 13080, 1887
The Electrician	April 12 1889, pp 655-657
Eastham, J.F., Laithwaite, E. R.	'Linear motor topology', Proc. IEE, 1973, 120, (3), pp 337 - 343
Eastham, J.F., Alwash, J. H.	'Transverse-flux tubular motors, Proc IEE, 1972, 119, (12), pp. 1709-1718
Ross, J.S.H., Anderson, A.F., Macnab, R.B.	Alternating Current dynamo-electric machine winding'. British Patent 1395152, 1975
Anderson, A. F., Bumby, J.R., Hassall, B. I.	Analysis of helical armature windings with particular reference to superconducting a.c. generators. Proc IEE, Vol 127, Pt C, No 3, May 1980 pp. 129 - 144. Download pdf file
Watnabe, M., Takahashi, M., Takahashi, N and Tsukui, T.	'Experimental study of a practical airgap stator arrangement for large turbine generators'. IEEE Winter Power Meeting, New York 1979, Paper F 79, 190-0
Conley, P. L., Kirtley, J. L., Hagman, W. H., Ula, A.H.M.S.	'Demonstration of a helical armature for a superconducting generator IEEE PES Summer Meeting Vancouver 1979 Paper F 79, pp 716-2