Comparison between plate and wound secondaries for linear induction motors with concentrated winding primaries

Concentrated windings that use planar non overlapping coils are simple in construction with comparatively narrow end regions. This leads to linear induction motor stators that can be butted together in sections to form long stator machines for urban transport and electromagnetic launch systems. The windings however produce two components of travelling field moving in opposite directions. The response of the plate rotor to the windings is therefore poor since opposing forces will be produced by the two fields. The use of a wound secondary rather than a plate dramatically improves the response. Here substantial emfs, currents and forces are produced only by the pole number for which the secondary is wound. The wound rotor therefore selects one of the fields produced by the concentrated winding for operation. The new principle is explored by the use of Finite Element Analysis and practical tests and it is shown that good force profiles and efficiencies are possible from concentrated stator wound rotor machines.