Single Phase Induction Motor

What is Induction Motor?

A motor can convert electrical energy into mechanical energy. The rotational part of this mechanical energy motor that rotates is called the rotor. And the part of the motor that is stationary is called the stator. In DC motors, we send the armature directly through the DC brush and commutator then the armature starts rotating. Here DC is said to flow directly to the motor. Single-phase induction motor is used whereas three phase induction motor is not required. We discussed here about single phase induction motor working principle, motor construction, motor advantages, disadvantages, and others.

But the funny thing is that in AC motors, the current goes to the stator. The stator of the AC motor is made up of many coils of copper wire. The magnetic flux that creates the magnetic flux between the AC windings is mounted on the motor horse. Since the AC is applied to the motor’s rotor through the air that produces the magnetic flux, it is called an induction motor. The main difference is the static transformer device and the rotating motor device. A Single-phase induction motor is a type of AC motor. This motor can run on a single-phase current only.

Single-phase induction motor construction

The construction of a single-phase induction motor is simply the body of the rotor is laminated with many laminations. Stamping is a type of seed made of silicon steel. The reason for basic laminating is to reduce eddy current loss in the motor while using silicone reduces the motor’s hysteresis loss. There are many grooves in the stumps arranged in a row. These are called slots.

The AC supplied with the copper wire or welding coils in the parts is either a single-phase or three phases. It creates a revolving magnetic flux in the AC’s vicinity, meaning that this magnetic flux can rotate as the motor’s revolving magnetic flux rotates. However, the speed at which the magnetic flux rotates is called synchronous speed. The magnet flux value of the magnetic flux created is always the same. Also, according to Faraday’s formula, this revolving magnetic flux generates an emf in the motor.

Working principle of single-phase induction motor

The working principle of a single-phase induction motor is not difficult and it is almost the same as a three-phase induction motor. Whenever the motor is connected to the AC supply then the alternating current starts flowing through the magnetic field and armature winding.


The field winding of the single-phase induction motor produces alternating flux (which is denoted by ɸ) that reacts with the alternating current flowing in the armature to generate torque. It is noted that there is no rotating flux produced in this type of machine.

Single-phase induction motor characteristics

Single-phase induction motor is one kind of AC motor. It is similar to the three-phase induction motor. Single-phase induction motor consists of the single-phase winding on the stator and squirrel cage rotor. It is noted that a three-phase motor is self-starting but a single-phase AC motor is self-starting. The operating characteristics are similar to the DC series motor, such as 

  • Due to the large armature current, the motor torque becomes very high, thus giving very high starting torque.

Types of single-phase induction motor

Single-phase AC motor is used whereas a three-phase supply is not required. The single-phase motor is more useable for company and residential purposes. It is true that a single-phase motor is less efficient than a three-phase induction motor. We know that there are two types of AC motors: Single-phase induction motors, and three-phase induction motors. There are four main types of single-phase induction motors, such as 

  1. It is noted that the starting winding is located 900 electrical from the main winding of the motor and a long period.
  2. Capacitor start motor. It is noted that a capacitor start motor is used where high starting torque is required, and starting period is much longer, such as compressor, industrial pumps, exhaust fans, high inertia loads, and others.
  3. Shaded pole motor. A shaded pole induction motor is very popular for low-rating motors or small operations (below 0.05 HP, or 40 watts) due to its simple construction. 
  4. AC series motor or Universal motor. The construction of the single-phase induction motor (AC series motor) is similar to the DC series motor. The AC series motor and DC series motor can be operated in both supplies. It means the DC series motor can be operated by applying a single-phase AC supply then the DC series motor behaves as an AC series motor. Some other motors are used for different purposes.

How to make a single-phase induction motor self starting?

We know that a three-phase motor is self-starting but a single-phase AC motor is not self self-starting motor. We should know why the induction motor is not self-starting. If you would like to make an induction motor self-starting, then you have to generate the revolving magnetic field.

The revolving magnetic field can be generated by converting a single-phase supply into a two-phase supply through the use of an additional winding. Whenever the motor reaches a sufficient speed the additional winding can be removed based on the type of motor (motor capacity). As a result, a single-phase induction motor can be made self-starting in this way.

Advantages of using a single-phase induction motor

The advantage of an induction motor is that it is made effortlessly. It does not have to do much work while using it, which means that maintenance costs are much less.

  • Single-phase induction motors can be quickly started, and no extra motors are required.
  • The price of these motors is much lower,
  • The motor’s efficiency is much higher, and the value of the power factor is much higher, most of the power given to the motor is used by the motor.

The disadvantage of using a single-phase induction motor

 We know that everything has a good and a wrong side. The disadvantage of using a single-phase induction motor is that.

  • AC motors are single-phase induction motors responsible for low power factors.
  • The efficiency of a single-phase induction motor is much less than that of a three-phase induction motor.

What are the applications of the AC series motor?

AC series motor is widely used in the factual condition due to its high speed and high starting torque. Basically, the AC series motor is used in the different sectors, such as

  • Vacuum cleaner
  • Sewing machine
  • Electric shaver
  • Drill
  • High-speed machine tools

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