Why induction motor does not runs at synchronous speed?

Answer 1

An induction motor cannot run at synchronous speed because it is the "slippage" of the rotor relative to the rotaing magnetic field that generates the current in the windings contained within the rotor. This induced (hence the term induction) current sets up the opposing magnetic fields that cause the rotor to rotate.

Answer 2

The torque produced by an induction motor depends on the current induced in the rotor. To have current induced in the rotor there must be a difference between the speed of the rotor and the speed of the rotating magnetic field. At synchronous speed the rotor current is zero and the torque must also be zero, so it never happens.

An induction motor runs at less than synchronous speed by an amount called the 'slip', defined by a formula:

s = (Ns - N) / Ns

Ns is the synchronous speed and N is the actual speed, so with a slip of 0.1 or 10% the actual speed is 10% less than the synchronous speed.

In a very simple model of an induction motor the current drawn and the output torque are both proportional to s.

Answer 3

An induction motor has to run at less than synchronous speed to allow currents to be induced in the rotor, without which there is no torque. The slip is defined as 1 - N/Ns where Ns is the synchronous speed and N is the actual speed. The torque is proportional to the slip, so no slip, no torque.

A typical induction motor runs at 2700 rpm on a 50 Hz system with a synchronous speed of 3000 rpm, so the slip is 1 - 2700/3000 or 10%.

Answer 4

Induction motors run on the principal of induction i.e the synchronous rotating magnetic field cuts the rotor windings inducing an emf in them. This emf causes current to flow in the rotor conductor which in turns produce a field which interact with that of the stator producing motion.

Now if the rotor was to run at synchronous speed,that would mean that the rotor would then be parallel to the rotating stator magnetic field. No rotor conductor would be cut,no emf induced in them,no current,no rotor magnetic field and hence no motion.

Synchronous motor run at synchronous speed because its rotor receive a DC current from an external source called an excitor.

Answer 5

The motor generates torque dependent upon the slip frequency (the lag between running speed and synchronous speed). Since the motor is not lossless, it takes some amount of slip to create the minimum amount of torque required to get the motor to turn.

Answer 6

The naturally-rotating magnetic field set up by the machine's field windings cuts the rotor bars of the rotor, inducing voltages into them which set up circulating currents. These currents link with the rotating field to produce the torque that drives the rotor. The rotating field rotates at synchronous speed. If the rotor turned at the same speed, then no voltages would be induced into the rotor bars, so no circulating current would flow, and no torque would be produced. So the rotor MUST rotate below synchronous speed.

Answer 7

The rotor must run at less than synchronous speed to allow low-frequency currents to flow in the rotor. At synchronous speed no currents are induced and no torque is produced.

Answer 8

if induction motor rotates at syn speed ...........there is no posibble to create relative motion between rotor and stator.....so net emf value is zero ....so motor cant run.......

Answer 9

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