Concept of slip in three phase induction motor

Apr 28 • General • 11142 Views • 4 Comments on Concept of slip in three phase induction motor

Three Phase Induction Motor:

  • A 3-phase induction motor is widely used electric motors in industry. It has a stator and a rotor. A stator carries 3 phase winding called stator winding and a rotor carries short-circuited winding called rotor winding.
  • 3-phase induction motor has simple and rugged construction. It is very cheap and requires little maintenance.


Concept of SLIP:

  • We know that, an induction motor consists of two assemblies i.e., rotor and stator.
  • The interaction of currents that is flowing in rotor and stator bars generate a torque. In an actual operation, the rotor speed always lags the magnetic field’s speed, thereby allowing the rotor bars to cut the magnetic lines of force and produce torque. This speed difference is called slip.
  • Therefore, the difference between the synchronous speed Ns of the rotating stator field and the actual rotor speed N is called slip.
  • The slip increase with load and is necessary for torque production. Slip speed is equal to the difference between rotor speed and synchronous speed. Percent slip is slip multiplied by 100.


  • Slip is expressed as a percentage of synchronous speed i.e.,

% of slip,s=(Ns-N/Ns) *100

  • The quantity Ns-N is sometimes called as slip speed.
  • When the rotor is stationary,slip s=1 or 100%
  • In an induction motor ,change in slip from no load to full load is hardly 0.1%to 3% so that it is essentially a constant speed motor.
  • Three phase induction motor is a particular form of transformer which has secondary winding rotating. In transformer, the frequency of primary and secondary winding is same but in induction motor the frequency of emf induced in rotor depends on slip.

Rotor emf frequency=s*sf ,

Where, sf is frequency of  applied voltage to stator.


Q1.What is a three phase induction motor?

Q2.What is a Slip in three phase induction motor?

Q3.What is rotor emf frequency?

Q4.What is %of  slip?

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