Answer / yuvi

Induction motor is nothing but a transformer with a
rotating short circuited secondary coil.

Applying AC supply to the field causes rotating magnetic
field influencing the armature. This induces secondary
current which inturn creates its own magnetic field.

Now we have two magnetic fields that react to each other.
The armatures magnetic field tries to catchup with the
rotating magnetic field of the field circuit causing the
armature to rotate. How ever, when the RPM equals RPM of
magnetic field, there wont be any variation in magnetic
field with respect to the armature and hence there will be
no current flowing through the armature, resulting in zero
torque. Hence there will always be a difference in RPM of
magnetic field and RPM of armature. This difference is
called slip.

Higher the slip>> Higher difference in RPM>> Higher
variation in flux crossing armature>> Higher armature
current >> Stronger magnetic field by armature >> Greater
torque the motot has.

Answer / virendra joshi

Above ans is correct but for better understanding s = Ns-
N where is a (synchronous) speed of magnatic flux & n is
the actual spee of the motor .

also %s = Ns - n / NS

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