> In an induction motor, speed is
>determined only by the frequency of the applied voltage, and not the
>voltage.

This is almost true but there is another small but significant effect.
(A Heavy Current man/woman may do a better job of explaining this  - feel
free).-

An induction motor is actually a rotary transformer and it works by
"slipping" the physically rotating cage relative to an electrically rotating
field that is produced by the AC supply. The difference between these two is
a low frequency component (typically in the low Hz region which is the
frequency which "induces" current in the rotor.

As you play with various voltage and current phase and amplitude
modification schemes you can (will) affect the slip frequency. As you push
the motor to its limits slip will increase and the motor will run slower
relative to the supply. Push it too far and it will suddenly not have enough
torque to continue to "chase" the rotating field and will tend to stall.

Summary: An induction motor's speed is relatively fixed but can be
controlled over a small range by maniuplating input voltage and
voltage/current relationships.

The speed is ALWAYS slower than the speed of the rotating field which
rotates at supplyu frequency or a sub-multiple thereof..



RM