Answer / eugene

Speed control control of induction type motors (also known
as squirral cage motors), are mainly achieved by
controlling the input voltage to the motor terminals. This
can be done by altering the frequency of the supply by
using a Variable Speed Controller, or if the speed control
is allowed to be multi-staged, resistive circuits can be
inserted using contactors and resistors, thus limiting the
voltage applied.

Answer / jaimin modi

1.control from stator side
a.by changing applied voltage
b.by changing stator no. of poles
c.by changing applied frequency

2.control from rotor side
a.by rotor rheostate
b.by cascade operation
c.by injecting emf in rotor ckt.

Answer / ravi roushan

through vfd.

Answer / karpagam

The motor speed control for controlling the speed
of an electric induction motor is by modulating the
amplitude and frequency of the driving voltage. When load
increases the speed control controls the speed of the
machine so as to be relatively constant with respect to
frequency of the driving voltage. Obviously,the speed
control controls the amplitude of driving voltage in
proportion to the square of the frequency.

Is a contactor (or master relay) required between incoming lines and a VFD? The question goes to safety. If a contactor were used before the VFD and an e-stop engaged then the motor will coast to a stop (i.e. VFD loses power) instead of stopping much faster if the VFD braking fucntion were used. It would make more sense to keep power on the VFD.

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