Answer Posted / pillay

the speed of an AC motor is dependent on number
of poles and frequency driving it as per the
speed formula already given by Mr sridher nayak
as SPEED =120f/p
So with the use of a frequency converter (vsd)one
can easily and safely vary the speed(by changing
the frequency to make the motor run at whatever
speed you want) OR
if your motor comes prewound with multiple pole
selectable winding, then with the help of change
over contactors you may have options for different
speed but they come with limitations in power and
fixed speed like 750,1000,1500 3000 rpm
Other means as rheostat, variable voltage and anything else will
not give you a safe, economical and reliable long term speed
control.

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