The implementation of a dual wound machine using a fractional slot winding

Christopher Hodge, Boyuan Yin, Xiaoze Pei, Fred Eastham, Vincent Zeng, Oliver Simmonds

Research output: Chapter or section in a book/report/conference proceedingChapter in a published conference proceeding


The benefits to be gained from high and directed energy weapons make them attractive, however they will require further electrification of warships. An important design requirement for the resultant total power system will be to achieve close integration between the weapons’ and ship’s power system segments, accounting for their differing time constants and establishing high levels of segregation and decoupling to minimise disturbances moving between the two segments. Above all the need to minimise cost and weight will dominate the design and its acceptability. A dual wound machine with two windings contained in the same stator slots, but nevertheless electrically isolated and magnetically decoupled from each other, will solve much of the system design challenge. The machine, employed as an alternator, with two independent outputs, one for each use, and yet driven by a single prime mover, and with little impact on overall length, will be highly attractive and may simplify the retrofit of high and directed energy weapons in mechanically propelled warships.
This paper describes the general background to a dual wound machine winding design including the calculation of its magnetic space harmonics, the requirements necessary to achieve magnetic decoupling between the two windings, and those to avoid unbalanced magnetic pull. These considerations lead to a dual winding of four and eight poles being the lowest pole numbers that give a practicable winding.
The paper then continues to describe a specific four and eight pole dual winding design aimed at installation on an existing laboratory machine at the University of Bath. Once rewound it is intended that the machine will serve as a small-scale demonstrator. The machine has 36 slots and while the four-pole winding can be achieved as an integral slot winding the eight-pole winding is by necessity fractional.
The resulting dual winding space harmonics are calculated by algebra and by a powerful computer method and these are used to demonstrate that the main pole face fluxes of the two windings do not couple magnetically. The winding is also analysed by two-dimensional flux modelling which confirms the main pole flux isolation and demonstrates that the tooth leakage flux does not lead to any loss of magnetic decoupling.
The demonstration that the end turn leakage flux does not lead to magnetic coupling between the two windings is left as one of the key design aspects to be demonstrated by the small-scale demonstrator.
Original languageEnglish
Title of host publicationINEC 2020: The 15th International Naval Engineering Conference and Exhibition
Number of pages10
Publication statusPublished - 8 Oct 2020


  • Electric Propulsion
  • Generators
  • Space Harmonics
  • Magnetic Coupling


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