Theory of Operation of an Induction Motor

A rotating field is organized when in stat or winding a 3 phase motor is kept. Due to this, a field is created which in returns sweeps past the conductor or rotor. And because of relative motion, in that conductor, induction of e.m.f. can be seen which in totality helps in the formation of rotor winding. The flow of current is in a direction which is completely opposite to the changing effect which is caused due to the winding. Now, the structure of this winding closely resembles a close circuit. This complete flow of current as per direction is as per Lenz’s law.

Ina rotor and its rotating field, its notable change is represented by relative motion. This motion opposes this rotating field and helps that rotor to run in a similar direction to that rotating field. Its main attempt is to pinpoint the motion in this case. When the current flows in the conductor or in rotor, it produces a torque. This production of torque is because of its essential requirement for causing rotation. These rotor conductors are positioned in the magnetic field, that too at aright angle.

As per this diagram represented above, a machine will only rotate against itself, that too against mechanical losses.And it happens in that instance when motor shaft is not loaded. In such cases, the synchronous speed has a very close proximity to rotor speed. Although both the speeds are very close but it does not mean that they are equal. This equivalency is not possible because if in case this happens, inside rotor winding, e.m.f. will be induced which again will become zero. All in all, there will not be any production of torque. In order to maintain this factor, it is always seen that the speed between the 2 remains slightly different.

In case a motor shaft is loaded, with respect to stat or rotation we can see the relative speed to be increasing in the stat or rotating field. This can only happen when the speed of rotor will slow down. After the induction of e.m.f. inside rotor winding, we can see it increasing. This, as a result,will produce rotor current more than the usual quantity. Therefore, this in totality will help in hiking the electromagnetic torque which is produced with the help of the motor.

We can obtain the conditions related to equilibrium when the adjustment of rotor speed is according to a new value. This is done to make sure that electromagnetic torque is in a sufficiently balanced with respect to load or mechanical torque when its application is on the shaft. In this case, speed of that motor will be slightly less than the considered no load speed. This comparison is accordance to that specific motor that is running under a full load condition.


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