When we discuss the detail of induction motors first thing needs to know what is the induction motor and types of induction motors. An induction motor is an AC electric motor in which the electric current in the rotor needed to produce torque is obtained by electromagnetic induction from the magnetic field of the stator winding.
Basically induction motor can be divided into two types depending on their power supply.
- Single-phase induction motor
- 3 phase induction motor
Now we discuss single-phase induction motors types and their construction.
Single-phase induction motors can be divided into 4 types according to their starting methods and construction.
- Split Phase Induction Motor
- Capacitor Start Induction Motor
- Capacitor Start Capacitor Run Induction Motor
- Shaded Pole Induction Motor
Now we discuss single phase induction motor types in detail.
Split Phase Induction Motor
The split-phase induction motor has a single cage rotor and two winding known as main winding and starts winding. The main winding has very low resistance and a high inductive reactance whereas the starting winding has high resistance and low inductive reactance. And split-phase induction motor also called resistance to start the motor. Because it starts winding connected with a resistor and it is used to get a phase difference between start winding and main winding.so that phase difference acts as a 2 phase power supply so now the induction motor gets the start. As soon this induction motor reaches synchronous speed and now starting winding automatically disconnect by using a centrifugal switch. This centrifugal switch connects series with starting winding it disconnects the path.
Capacitor Start Induction Motor
The capacitor starts induction motor the same as the split-phase induction motor but the main difference is the capacitor connect series with start winding. This capacitor used to get a grate phase difference between the main winding and start winding and it helps to start the induction motor. Also capacitor start induction motor has a centrifugal switch and it works like as centrifugal switch on a split-phase induction motor.
Capacitor Start Capacitor Run Induction Motor
This type of induction motor same as the capacitor starts motor but the capacitor starts the capacitor run induction motor has two capacitors, one is starting capacitor and the other one running capacitor. Both capacitors are connected parallel with main winding and series with starts winding. This induction motor centrifugal switch work as the other two types but it connects series only starts capacitor.
Shaded Pole Induction Motor
Shaded pole induction motor is a simple self-starting motor and it makes pole shaded by a copper ring. This ring used to start the induction motor and it also called a shaded ring. The shaded pole induction motor rotates only one direction it can’t rotate other direction.
Now we discuss Three-phase induction motors types and their construction.
Three-phase induction motors can be divided into 2 types according to their starting methods and construction.
- Squirrel Cage Induction Motor
- Wound Rotor or Slip Ring Induction Motor
Squirrel Cage Induction Motor
Squirrel cage induction motor is a type of 3 phase induction motor, its functions work by using electromagnetism. This motor called squirrel cage induction motor because its rotor looks like a squirrel cage also called a squirrel cage rotor. This rotor had made by using a highly conductive metal. The stator winding connects with 3 phase power supply and then it generates a rotating magnetic field. The rotating magnetic field produces induce a current in the rotor, which induces current generate its magnetic field. This magnetic field and stator magnetic field interaction make torque on the squirrel cage rotor.
Squirrel cage induction motors most of the use of industrial applications because of self-starting motor and easy to adjust.
Advantages of squirrel cage induction motor
- Good speed regulation.
- Low cost and less maintenance.
- Less weight and small.
- Good heat regulation.
Disadvantages of squirrel cage induction motor
- Poor speed control.
- High starting current and poor starting torque.
- Machine tool.
- Lathes and milling machines.
- High power fans and blowers.
Wound Rotor or Slip Ring Induction Motor
Slip ring induction motor the same as the squirrel cage induction motor but the main difference is rotor construction. These rotors have rings is used to connect the rotor winding into an outer high variable resistor. This high variable resistor makes low current in rotor winding and it generates high starting torque. This motor variable resistor can be used to speed control and it is an advantage over squirrel cage induction motor.
Advantages of slip ring induction motors
- Good inbuilt speed control system.
- Low starting current and high starting torque.
Disadvantages of slip ring induction motors
- High cost comparing with squirrel cage induction motor.
- Complex design and need more maintains.
Therefore slip ring induction motors are generally employed where load requires high starting torque or good speed control. They are employed in hoists, elevators, compressors, printing presses, large ventilating fans, loads requiring speed control such as for driving lifts and pumps.