Induction Motors: Explained.

 

Induction Motors:

            Single-phase induction motors require just one power phase for their operation. They are found in domestic as well as industrial use.

Structure:

            The main components of single-phase induction motors are:

A rotor is a rotating part.

A stator winding is stationary and it has two parts.

Stator Winding:

            Stator winding consists of two parts. One is main winding and another one is auxiliary winding. The auxiliary winding is placed perpendicular to the main winding. A capacitor is connected in auxiliary winding. Let's assume there is only one coil in the main and auxiliary winding to understand its working better. Assume that no current is flowing through auxiliary winding. A see current passing through the main winding will produce a fluctuating magnetic field.

Working of single phase Induction Motor:

            The working of a single-phase induction motor is simple. Just put one rotor which is already rotating inside such a magnetic field. You can note one interesting thing that the rotor will keep on rotating in the same direction. The reason is that the fluctuating field is equivalent to the sum of two oppositely rotating magnetic fields. This concept is known as double-revolving field theory. The effective rotating magnetic field on the rotor is interesting. Since the magnetic field is varying electricity is induced in rotor bars due to electromagnetic induction. So, here is a situation that current-carrying bars are immersed in a magnetic field. This will produce a force according to Lawrence law. So, the rotor will start rotating. But here we have got two such oppositely rotating magnetic fields, so torques produced by them will be equal and opposite. The net effect will be zero torque on the rotor so, the rotor won't start and it will simply buzz. But if we can somehow give this rotor an initial rotation, one torque will be greater than the other. There will be a net torque in the same direction of initial rotation. As a result, the loop will keep on rotating in the same direction. This is the way that the single-phase induction motors work.

But one big problem remains how to provide such an initial rotation. Nikola Tesla, a famous Yugoslav inventor, suggested one ingenious solution to this problem: if we can cancel any of the rotating fields, we will be able to start the motor. The auxiliary winding come capacitor arrangement is used exactly for this purpose. Auxiliary winding also produces two oppositely revolving magnetic fields. One of them will cancel RMF of the main winding and the other will get added up. The resultant will be a single magnetic field, which revolves under a specific speed. Such a magnetic field can give starting torque to the rotor or the motor will cell start after the rotor has attained a specific speed even if you cut the auxiliary winding it will keep on rotating as explained earlier. This cutting action is done through a centrifugal switch.

That's all about working off single-phase motors.

 

Stay tuned.

Bye.