Why Induction Motor cannot run at Synchronous Speed | Slip Phenomenon

The Induction Motor cannot run at Synchronous speed because the Slip is never zero in an Induction Motor. Now the question arises, why slip is never zero in an induction motor. So in this article, we will discuss the total concept of What is Synchronous speed, What is Slip in an induction motor, etc.

What is Synchronous Speed?

In simple words, the speed of the rotating magnetic field in the stator winding of the three-phase induction motor is called Synchronous Speed.

The equation of synchronous speed in the induction motor is,

From the above equation, we can say the synchronous speed depends upon the frequency of the power supply, and magnetic poles. We know that our supply frequency is always constant, and the no. of poles is also constant which means the synchronous speed will be constant.

What is Slip in Induction Motor?

The difference between the rotating magnetic field or synchronous speed and rotor speed with respect to synchronous speed is called Slip.

Slip is measured in percentage. The formula of Slip in an induction motor is,

Here, Ns = Synchronous Speed

          Nr = Rotor Speed

Why Induction Motor cannot run at Synchronous Speed?

The answer to this question can be given in two ways. All are given below to understand easily.

1. The first answer can be given as the torque developed in the rotor is proportional to the Slip. If the rotor runs at synchronous speed then there will be no difference between the synchronous speed and rotor speed, so the Slip will be zero, hence no torque will be developed and the rotor will slow down.

2. The above answer was theoretical. If we see practically when the rotor runs at synchronous speed, there will be no relative speed between them which means both are static with respect to each other. For this reason, the relative motion between the magnetic field and the rotor conductor will be zero, and thus no EMF will be induced in the rotor conductor.

As there no EMF is induced, no current will flow through the rotor conductor and also no flux will be produced and ultimately no torque will be developed and the rotor will slow down.

Read Also:

• Why Three Phase Induction Motor Self-Starting but Synchronous Motor not?
• Why DC is used not AC for excitation of Synchronous Alternator and Motor?
• Difference between Generator and Alternator Full explanation.

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