Abstract: A pole-amplitude modulation (P.A.M.) three-phase, pole-number changing machine having star-connected and delta-connected stator winding components, thereby providing additional means for reducing m.m.f. harmonics in the resultant three-phase field. Pole-number changing is effected by reversing the star-connected winding component relatively to the delta-connected component.A design method defines relationships between alternative pole-numbers and stator slot number, and slot-spacing between star- and delta-connected components.

Abstract: The invention provides improved stator windings for pole-amplitude modulation (P.A.M.) pole-changing electric motors and generators. In large machine of high pole-numbers, the effect of adjacent harmonics of m.m.f. waveform becomes evident in the form of low-frequency vibration of the frame. In small machines the effect, although present, is less important. The invention provides stator windings, particularly for large machines, wherein the phase-winding coil grouping, selected primarily for sinusoidal modulation, is selected secondarily to include a third-harmonic content, whereby the adjacent harmonic m.m.f. content may be reduced for both alternative pole-numbers.

Abstract: Three-phase, alternating current, pole-amplitude modulation (P.A.M.) pole-changing electric motors or generators having series/parallel connection of phase winding parts for the alternate pole-members. To obtain approximately equal air-gap flux-density for both pole-numbers, selected coils are provided in branch connection with the main phase winding parts and switched in circuit for one pole-number only. Such selection, to be consistent with normal coil-reversal requirements of pole-changing by P.A.M., is shown to necessitate branch coils represented by similarly angularly positioned vectors in each phase-winding and of equal number in the reversed and non-reversed phase-winding parts.