THREE-PHASE ROTATING FIELDS The three-phase induction motor also
operates on the principle of a rotating magnetic field. The
following discussion shows how the stator windings can be
connected to a three-phase ac input and have a resultant
magnetic field that rotates. Figure 4-4, views A-C show the
individual windings for each phase. Figure 4-4, view D, shows
how the three phases are tied together in a Y-connected stator.
The dot in each diagram indicates the common point of the
Y-connection. You can see that the individual phase windings are
equally spaced around the stator. This places the windings 120°
apart. Figure 4-4. - Three-phase, Y-connected stator. The three-
phase input voltage to the stator of figure 4-4 is shown in the
graph of figure 4-5. Use the left-hand rule for determining the
electromagnetic polarity of the poles at any given instant. In
applying the rule to the coils in figure 4-4, consider that
current flows toward the terminal numbers for positive voltages,
and away from the terminal numb