AC MACHINES-1 (66761) Theory
10. Realize the principle and construction of 3-phase induction motor.
10.1. Explain the general principle of induction motor.
BASIC PRINCIPLES
Motors work through the principles of electromagnetism. If you run electricity through a wire, it creates a magnetic field. If you coil the wire around a rod and run electricity through the wire, it creates a magnetic field around the rod. One end of the rod will have a north magnetic pole and the other will have a south pole. Opposite poles attract one another, like poles repel. When you surround that rod with other magnets, the rod will rotate from the attractive and repulsive forces.
Working Principle of an Induction Motor
The motor which works on the principle of electromagnetic induction is known as the induction motor. The electromagnetic induction is the phenomenon in which the electromotive force induces across the electrical conductor when it is placed in a rotating magnetic field.
An induction motor (also known as an asynchronous motor) is a commonly used AC electric motor. In an induction motor, the electric current in the rotor needed to produce torque is obtained via electromagnetic induction from the rotating magnetic field of the stator winding. The rotor of an induction motor can be a squirrel cage rotor or wound type rotor.
Induction Motors are the most commonly used motors in many applications. These are also called as Asynchronous Motors, because an induction motor always runs at a speed lower than synchronous speed. Synchronous speed means the speed of the rotating magnetic field in the stator.
There basically 2 types of induction motor depending upon the type of input supply - (i) Single phase induction motor and (ii) Three phase induction motor.
Basic working principle of an Induction Motor
In a DC motor, supply is needed to be given for the stator winding as well as the rotor winding. But in an induction motor only the stator winding is fed with an AC supply.
An AC motor works by applying alternating current to stator windings, which produce a rotating magnetic field. Because the magnetic field rotates in this way, an AC motor does not need power or mechanical aid to be applied to the rotor.