EFFECTS OF POLE FLUX DISTRIBUTION IN A HOMOPOLAR LINEAR SYNCHRONOUS MACHINE

Linear forms of synchronous electrical machine are at present being co nsidered as the propulsion means in high-speed, magnetically levitated (Maglev) ground transportation systems. A homopolar form of machine i s considered in which the primary member, which carries both ac and dc windings, is supported on the vehicle. Test results and theoretical p redictions are presented for a design of machine intended for driving a 100 passenger vehicle at a top speed of 400 km/h. The layout of the dc magnetic circuit is examined to locate the best position for the dc winding from the point of view of minimum core weight. Measurements o f flux build-up under the machine at different operating speeds are gi ven for two types of secondary pole: solid and laminated. The solid po le results, which are confirmed theoretically, show that this form of construction is impractical for high-speed drives. Measured motoring c haracteristics are presented for a short length of machine which simul ates conditions at the leading and trailing ends of the full-sized mac hine. Combination of the results with those from a cylindrical version of the machine make it possible to infer the performance of the full- sized traction machine. This gives 0.8 pf and 0.9 efficiency at 300 km /h, which is much better than the reported performance of a comparable linear induction motor (0.52 pf and 0.82 efficiency). It is therefore concluded that in any projected high-speed Maglev systems, a linear s ynchronous machine should be the first choice as the propulsion means.