An induction motor is also known as asynchronous motor which uses the electric current to produce torque. This torque is generated by electromagnetic induction or permeability from the magnetic field of the stator winding in the motor.
Different from a DC motor, supply is not needed to be provided for both the stator winding and rotor winding, it is only needed in the stator winding through an AC supply.
There are two phases of induction Motor which are categorised in consideration of their slip (difference between the stator speed and rotor speed) and input supply. They are; 3 phase induction motors and Single phase induction Motors.
We are going to major on single phase induction motors. They are commonly exploited in our normal residential applications such as air conditioners, dry cleaners, ovens, fans, fridges etc.
We have different types of single phase induction motors;
- Shaded pole induction motor
- Permanent split capacitor motor
- Split Phase induction motor
- Capacitor start Capacitor run induction motor
- Capacitor start inductor motor
Split phase Inductor Motor
Alternatively known as Resistance Start Motor .It is characterised by a single cage rotor, and its stator has two windings; main winding and starting winding .It is used in a vast way.
In split phase induction motor the starting and main current get splitted from each other at 90 degrees hence its name. An auxiliary or starting winding is added to the main or running winding to make sure that the single phase induction motor is self-starting. In order to achieve the goal of self-starting in a single phase induction motor, we should produce a rotating magnetic field. A centrifugal switch is connected in series with the starting winding to automatically disconnect the starting winding from supply when the motor has reached 70 to 80 percent of its induction load speed.
Capacitor Start Induction Motor
This motor is relatively similar to the Split phase Inductor Motor. The only difference is that in this motor, a capacitor is connected in series to auxiliary winding. The additional winding provides the starting torque. The speed produced by this motor is higher than that produced by the split phase induction motor. Once the speed is picked, the additional winding along with capacitor are of no use anymore and they are removed from the circuit with the help of centrifugal switch. These kind of motors possess very high starting torque up to 300% full load torque. Applications; in conveyors, grinder, air conditioners and compressor.
Permanent Capacitor Induction Motor
A low capacitor is connected in series with the starting winding and is not removed from the circuit even in running condition or when speed is picked, therefore, a centrifugal switch is not necessary. It has a cage rotor and stator, whereby the stator has two windings – main and auxiliary winding. It does not possess a starting switch. Has higher efficiency and pull out torque. Applications; in fans, blowers in heaters and air conditioners.
Shaded pole induction motor
The stator has projected poles which are shaded by copper band or ring which is inductive in nature. The poles are then divided unevenly into two. The smaller fraction is shaded and carries the copper band. This motor is quite different from the rest in terms of operating system. It doesn’t use any auxiliary winding or even a rotating field. Rather it has a field that sweeps across the pole faces which has enough ability to drive the motor. So the field moves from one side of the pole to another side of the pole simultaneously. Applications are; hair dryers, toys, record players, small fans and electric clocks.