Electromagnetism : Three phase Motor

Factories!!!! Conveyor belt machines!!!! Mixer!!!. These three things has something one in common. That is really fascinating us to know what is the common thing. Let me give you clues. These three things usually used in factories and some used in homes to. It rotate all time depends on user and it's cheap. Well dummies if you guess three phase induction motor, and you are right. Dummies lets learn about three phase induction motor that going to amaze your mind.

The picture above shown is the exploded view of three phase induction motor. The main two parts of AC three phase induction motor is the stator and Rotor.The stator is the stationary part and the function as you know earlier that produce rotating magnetic field. The rotor is the rotating part. The rotor is a squirrel cage design that short circuit in end rings. These will allow rotor to rotate by inducing magnetic field in rotor.

Lets go to the interesting part. It's the working principle of Three phase motor.  If you compare single phase induction motor, you can easily spot the difference in three phase motor. Like in three phase motor has Three phase windings. Means each phase has it's own windings. When the three phase supply flows to the each stator windings and it will energize. The energize each phase windings will give a rotationg magnetic field that runs  at synchronous speed. To calculate the synchronous speed the formula is : 

While the rotating magnetic field runs in synchronous speed, the rotating magnetic field will energize the rotor. This will produce and EMF in the rotor and produce a force to rotate the rotor by Lorentz's force law. This rotation will make a three phase sinusoidal wave. This means each phase has it'a own sinusoidal wave in order to rotate the rotor.

It's look interesting to see how this three phase motor works. But there's a little glitch in the rotor. Like in synchronous motor, the rotor with permanent magnet or external DC power supply, will follow the stator rotating magnetic field in constant synchronous speed even load is added. But in this induction motor, The rotor first follow the synchronous speed. Eventually the when the both stator's rotating magnetic field and rotor comes with same speed, it will slow down and speed up again. This rotor speed never achieve the synchronous speed. This phenomena called 'Slip' Note that dummies. To calculate the slip the formula is :

Every things has benefits and some drawbacks. Same goes to this induction motor dummies. The advantage is less maintenance and less cost. this is why it's widely used in factories. Furthermore, it also has self starting that doesn't require external force or adding special windings.

 The disadvantage of this induction motor is it produce huge amount of heat actually can fried an egg :P just kidding,There's a fan mount back of the motor to dissipate the heat. The torque is reduce when load is added and didn't make constant synchronous speed. Finally it has less efficiency than a synchronous motor.

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