An asynchronous motor is a motor that physically spins or rotates slower than the rotation of the electromagnetic field that powers it. Let’s elaborate on that.
How It Works
A squirrel cage motor is a type of induction motor, we know that this type of motor works on the principle of electromagnetic induction. When power is applied, there is an electromagnetic field produced in the stator that rotates around and around at the speed of the supply frequency (coupled with some other factors). When this rotating magnetic field cuts through the bars of the squirrel cage rotor it induces current which causes another magnetic field in the rotor to appear. These 2 magnetic fields, one in the stator and one in the rotor now work in conjunction with each other to physically spin the rotor.
Now For The Interesting Part…
The reason there was any hope of creating a magnetic field in the rotor in the first place was because of the difference in speed between the stators rotating magnetic field and the rotor speed itself. This difference in speed between the two is called the slip speed.
As the rotor starts spinning faster and faster and catching up to the stators magnetic field speed, it will come to a point where the rotor will stabilise and not reach the same speed as the stators rotating magnetic field. This is because if the rotor were to spin at the same speed as the stator field (synchronous speed), the stator field would not be able to cut through the bars of the rotor and cause induction to produce a magnetic field. No magnetic field in the rotor, no spinning action. There always has to be a difference in speed between the 2 to enable the rotor to spin. This is what’s known as an asynchronous motor.
To Recap
The rotating magnetic field in the stator causes an induced magnetic field in the rotor. These 2 magnetic fields work to physically turn the rotor.
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