Induction Machine Windings and Their mmfs

Authored by: Ion Boldea

Induction Machines Handbook

Print publication date:  June  2020
Online publication date:  May  2020

Print ISBN: 9780367466121
eBook ISBN: 9781003033417
Adobe ISBN:


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The fundamental concept of magnetomotive force (mmf) as the source of a travelling magnetic field in the airgap of induction machines (IMs) is introduced, first produced with three-phase alternative current (A.C.) windings (coils), then with two-phase A.C. windings (for single-phase A.C. source supplies), and finally (new) with multiphase (5, 7, 2 × 3, 3 × 3 phases) A.C. windings, introduced recently. The placement of A.C. windings in slots is discussed in detail. The winding factor’s three components for distributed windings (integer or fractionary slot/pole/phase, q ≥ 1) are derived both for the fundamental component (average torque producing) and mmf space harmonics. Finally, the “skewing” mmf concept is introduced, only to be, later in this book, used to prove the axially non-uniform magnetic saturation of the stator core, especially at high currents (above 2–3 p.u.; p.u. means relative values to rated current).

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