Slip of Induction Motor
We know that an induction motor produces 2 fluxes. One is
stator flux and the other is rotor flux. The stator flux is also called the
main flux. And from this main flux, the rotor flux is made in the process of
induction. You can read this article to know how stator and rotor flux is
made.
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The speed of the stator flux of a motor is also called
synchronous speed. Induction motors never run at synchronous speeds. And this
synchronous speed will always be higher than the speed of the rotor. But why?
What is the problem if it is equal?
Why Synchronous speed of the induction motor is not equal to rotor speed.
We consider an induction motor that runs at
synchronous speeds. Then the rotor coil will be fixed relative to the magnetic
field. And there will be no voltage induction. And if no voltage is induced, no
current will flow through the rotor.
As a result, no magnetic field will be
created in the rotor and the amount of induced torque will be zero. Then the
rotor speed will gradually decrease due to friction and will stop at one stage.
The induction motor can travel at speeds close to
synchronous speeds but not at speeds equal to perfectly synchronous speeds.
Because if it runs at synchronous speed then the motor will stop.
What a slip
The difference between the speed of the rotor flux as
far as the rotor flux is behind the synchronous speed of the motor or the speed
of the rotor flux is called slip. The slip is basically expressed by S. Slip
values range from 2% to 6% when the motor is running at full load.
Here,
S = motor slip
NS = speed of motor stator flux or synchronous speed
N = Speed of motor rotor flux or rotor speed
That is, with a slip we can basically measure the
speed of the rotor relative to the stator speed. Now if,
NS = Synchronous speed of the motor, Revelation Per Minute
or R.P.M unit.
NR = Rotor speed R.P.M units.
Then we can also express the slip speed of the motor
in the following way.
We can also call the part of the slip Per Unit Slip or
Functional Slip. This Per Unit Slip is called Motor Slip.
From the above equation, we can find the speed of the
rotor.
And we can also express slip with angular velocity.
Slip requirements
The requirement of a slip in the induction motor is
undeniable. We know that the difference between synchronous speed and the
relative speed of the rotor is called slip. And as a result of this relative
speed, voltage is induced in the rotor. So we can say,
Again the current flow in the rotor due to that
induced voltage. So,
And the torque is generated in the rotor depending on
the rotor current.
We know from the equation of torque,
Thus the production torque in the rotor depends on the
industry.
By this equation, we can understand the relation of
slip to torque. This means that the higher the value of the slip, the more
torque will be induced in the rotor. And the more torque is induced, the higher
the rotor speed. The speed of the induction motor can be changed a lot through
this slip.
The slip of the motor is reduced when the load of the motor is low.
And when the motor is running at full load, its slip is kept at maximum so that
more torque is induced.