Alternating current (ac) windings in electrical machines basically have a twofold purpose. In electrical generators ac windings are place where electromotive force (EMF) should be induced. In electrical motors, primarily ac windings goal is to produce rotating magneto-motive force (MMF) wave. In any case, ac windings should be designed in such a manner that induced EMF or generated rotating MMF wave consists predominantly of the fundamental sinusoidal component. Therefore, the starting point of an induction machine study is the analysis of MMF waves in the air gap of such machines. This assumes knowledge of winding distribution along the air gap from stator as well as from rotor side. The magnetic flux is analogous to the electric current. The MMF which sets up the magnetic flux is analogous to the EMF. The MMF is equivalent to a number of turns of wire carrying an electric current. If either the current through a coil (as in an electromagnet) or the number of turns of wire in the coil is increased, the MMF will be higher; and if the rest of the magnetic circuit remains the same, the magnetic flux increases proportionally [1]. At least two different approaches exist for describing winding distribution.

Chapter Contents:

• 4.1 Current sheet concept
• 4.2 Winding function concept
• 4.2.1 Concentrated full-pitch coil MMF
• 4.2.2 Distributed full-pitch phase winding
• 4.2.3 Pulsating MMF
• 4.2.4 Three-phase full-pitch (single-layer) winding
• 4.2.5 Three-phase shorted-pitch coil (double-layer) winding
• 4.3 Rotating MMF wave - analytical approach
• 4.4 Fractional slot winding
• 4.5 Wound rotor MMF space harmonics
• 4.6 Cage rotor MMF space harmonics
• References

Inspec keywords: magnetic flux; stators; induction motors; electric potential; rotors

Other keywords: electromotive force; fundamental sinusoidal component; induced EMF; magnetic flux; air gap; rotating magneto-motive force wave; rotor side; electrical generators; electric current; generated rotating MMF wave; three-phase induction motors; magnetic circuit; electrical motors; induction machine study; winding distribution; ac windings; stator; alternating current windings; electrical machines

Subjects: Electrostatics; Asynchronous machines