Mechanical Systems 379
flux in the main poles induces a voltage into the shaded sections of the
poles. Since the shaded section acts like a transformer secondary, its volt-
age is out of phase with the main field voltage, as shown in the waveform
diagram of Figure 14-22. Note the four time intervals that are shown in se-
quence in Figure 14-22. The voltage induced in the shaded pole from the
main pole field causes movement of the rotor to continue. Study Figure
14-22 carefully to understand the basic operating principle of the shaded-
pole AC induction motor more fully.
The shaded-pole motor is inexpensive, since it uses a squirrel-cage
rotor and has no auxiliary starting winding or centrifugal mechanism.
Application is limited mainly to small fans and blowers, and other low-
torque applications.
Repulsion Motors—Another type of AC induction motor is the repul-
sion-start induction motor. This motor was once used for many applica-
tions, but is now being replaced by other types of single-phase motors.
The principle of operation of the repulsion motor provides an interesting
contrast to other induction motors.Figure 14-21. Other types of capacitor motors: (A) Capacitor-start, capacitor-run
motor, (B) Permanent capacitor motor