374 Electrical Power Systems Technology
pole becomes a south polarity. The rotor will align itself horizontally, since
no polarity is developed in the vertical poles at this time. Now, as we prog-
ress to time t 2 , phase 1 is minimum and phase 2 is maximum. Assume that
the upper stator pole becomes a south polarity, and the bottom stator pole
becomes a north polarity. The rotor will now align itself vertically, by mov-
ing 90°. At time t 3 , phase 1 becomes maximum in the opposite direction,
and phase 2 is minimum. This time interval results in a north pole on the
left and a south pole on the right. Thus, the rotor moves 90° further in a
clockwise direction. This effect will continue as two-phase voltage is ap-
Figure 14-17. Illustration of how AC motors develop rotation: (A) Single-phase
situation, (8) Two-phase situation, (C) Three-phase situation