A single phase induction motor is the one which operates on a single phase AC power source. This motor is used in the applications where requirement of power is low. It is generally used in domestic applications because of limited size and less power. Some of the uses include fans, washing machines, pumps, toys, vacuum cleaners, refrigerator compressors and in machine tools.
First I will tell you about its construction, followed by working principle and advantages. And in the last sections of this article, I will share some knowledge about the starting problem of a single phase induction motor and give a comparison of 3 phase and single phase induction motors. Let’s now take a look on construction of a single phase induction motor.
Construction of Single Phase Induction Motor
- The basic construction of Single Phase Induction Motor is similar to all other motors.
- A rotor and a stator are the two main components of Single Phase Induction Motor.
- We will have a look at both Stator and Rotor one by one below.
- So, first of all have a look at the functionality of Stator of Single Phase Induction Motor:
Stator of Single Phase Induction Motor
- The stator of a single phase induction motor is the stationary part as in other motors.
- The stationary stator of the motor is supplied with an AC power supply which is single phase.
- Stator is a cylindrical frame having slots.
- Inside the stator frame, cylindrical core of rotor is placed with a little air gap in between them.
- The purpose of making slots is to carry winding circuit.
- The winding circuitry of stator is called stator winding which in the case of this particular motor is single phase.
- Squirrel Cage Induction Motor.
- Wound Rotor Induction Motor.
- 3 Phase Induction Motor.
- Introduction to Synchronous Motor.
Rotor of Single Phase Induction Motor
- The second basic part of motor is the rotor.
- As in all other motors, the rotor is the rotating part.
- Rotor is cylindrical in shape and it is connected to the output shaft of the motor.
- In other words, this is the part which supplies rotation at the output. Load is connected to the shaft of rotor.
- Rotor of a single phase induction motor is similar in construction with a squirrel cage 3 phase induction motor. I have explained its construction in my article on 3 phase induction motor.
- Rotor has slots on all over its surface to carry conductors that are copper or aluminum bars.
- These conductor bars are short circuited with each other by two end rings. One end ring is on each side of rotor.
- Just like rotor of a squirrel cage 3 phase induction motor, it has no slip ring and brush assembly.
- That was all about basic structure of stator and rotor, now I am moving towards next section of this article.
Working of Single Phase Induction Motor
The working principle of a single phase induction motor is based on Faraday’s law of electromagnetic induction. AC supply is given to stator windings which is single phase, the current flowing through the winding will produce a magnetic field which is called stator magnetic field. The flux lines of this magnetic field will cross the conductors of rotor. As the flux is changing due to changing magnetic field of AC supply with time, an emf and current will be induced in the rotor. The induced current will give rise to another magnetic field which is called rotor magnetic field. A single phase induction motor differs in operation from a 3 phase induction motor in the sense that this motor cannot generate a rotating magnetic field. Instead of a rotating magnetic field, it produces a magnetic field which pulsates due to AC oscillations between 0 and 180 degrees. In other words, the magnetic field does not rotates but reverses 180 degrees. The interaction of the two magnetic fields or magnetic fluxes, one from stator and second from rotor will produce torque.
Advantages of Single Phase Induction Motor
In this section, I am highlighting some of the advantages of a single phase induction motor which are as under.
- A single phase induction motor is more economical where less power is required.
- Such motor is simple in construction because of absence of slip rings and brushes.
- Because of simple construction, it is very easy to maintain and repair.
- This motor is cheap in cost.
- Also, single phase induction motors are reliable and robust.
Starting Problem of a Single Phase Induction Motor
The initial torque or starting torque of a single phase induction motor is very low so this motor cannot take a self start. For 3 phase induction motor the starting torque is high so it can start on its own. Now to overcome this starting problem, capacitor can be used to build the starting torque. This capacitor creates a phase difference between the flux of rotor and flux of stator. The capacitor is used with a starting winding which is switched off once the motor is started.
Comparison of Single Phase and 3 Phase Induction Motors
In this segment of my article, I am going to give a little comparison of single phase and 3 phase induction motors so you can get an idea which one is best for your application. Both are compared on the basis of their features, construction, supply and uses.
- The output produced by a single phase induction motor is about half as produced by 3 phase induction motor.
- A single phase induction motor is used where less power is required as compared to 3 phase induction motor.
- The efficiency and power factor is also low in case of single phase induction motor.
- Single phase motors are simple and cheaper for small rating as compared to 3 phase induction motors.
- Starting torque is low in single phase motor as compared to 3 phase induction motor.
- Single phase induction motors are used for domestic applications while 3 phase induction motors are used in industrial applications.
- Maintenance of a single phase motor is very easy in contrast with 3 phase induction motor.
- Another important point is the construction. It’s easy to construct a single phase induction motor as compared to 3 phase induction motor.
- Single phase induction motor is reliable and economical if compared to 3 phase induction motor.
- 3 phase induction motor is self starting while single phase induction motor is not a self starting motor.
