AC Motors
AC MOTOR TYPES
Figure 6 Split-Phase Motor
Single-Phase AC Induction Motors
If two stator windings of unequal impedance are spaced 90 electrical degrees apart and connected
in parallel to a single-phase source, the field produced will appear to rotate. This is called phase
splitting.
In a split-phase motor, a starting winding is utilized. This winding has a higher resistance and
lower reactance than the main winding (Figure 6). When the same voltage VT is applied to the
starting and main windings, the current in the main winding (IM) lags behind the current of the
starting winding IS (Figure 6). The angle between the two windings is enough phase difference
to provide a rotating magnetic field to produce a starting torque. When the motor reaches 70 to
80% of synchronous speed, a centrifugal switch on the motor shaft opens and disconnects the
starting winding.
Single-phase motors are used for very small commercial applications such as household
appliances and buffers.
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