The MMF and Field Distribution of an AC Winding

This chapter introduces the "forcing function" of the magnetic field of a typical AC machine, namely the stator magnetomotive force (MMF). The stator MMF primarily acts to magnetize the machine and is accounted for, in the per phase equivalent circuit, by the magnetizing inductance. The chapter explores MMF distributions for two‐pole, single‐circuit machines, and discusses the actual number of electrical poles, however, depends on design considerations. This number is nearly always greater than two since two‐pole machines are particularly wasteful of stator conductors due to large return paths at the end of the machine (end windings). The chapter shows a schematic representation of a single‐phase full pitch winding, and fractional pitch winding. Windings are generally distributed in several slots in order to better utilize the available space around the periphery of the machine. In most cases, winding distributions are nearly always symmetrical if the number of slots per pole per phase is two or greater.