Types of AC motors – Classification and uses of alternating current motors


We all know that without electricity, we cannot do any of our job. If we look into the world we live in, the major development in technology and civilization took place only after the introduction of electricity and electrical devices. Can we imagine a life with out air conditioners/ceiling fans, lights, computers and communication devices and many more.

So it is quiet evident that electricity and electrical equipments play a vital role in every inch of our life. One such equipment which created a giant leap to the mankind in both domestic & industrial sectors is the "Motor". The usage of AC motors is much more prevalent than DC motors due to several practical reasons which we shall learn later on.

Electric Motor

A.C. Motors are playing a very vital role in everyday life, right from pumping water to overhead tank to modern robot's manoeuvring arm. The main factor which lead to the adoption & wide usage in various fields is its flexibility and its huge variety which can be matched with almost any kind of demand. To know what are the different types of A.C.Motors available, to match it perfectly with the demand, it is highly essential to know about the different classifications of A.C.Motors.

Types of AC Motors

  • Classification Based On Principle Of Operation:

(a) Synchronous Motors.

1. Plain

2. Super

(b) Asynchronous Motors.

1. Induction Motors:

(a) Squirrel Cage

(b) Slip-Ring (external resistance).

2. Commutator Motors:

(a) Series

(b) Compensated

(c) Shunt

(d) Repulsion

(e) Repulsion-start induction

(f) Repulsion induction

  • Classification Based On Type Of Current:

1. Single Phase

2. Three Phase

  • Classification Based On Speed Of Operation:

1. Constant Speed.

2. Variable Speed.

3. Adjustable Speed.

  • Classification Based On Structural Features:

1. Open

2. Enclosed

3. Semi-enclosed

4. Ventilated

5. Pipe-ventilated

6. Riveted frame-eye etc..

a closed motor


squirrel cage rotor

ceiling fan

synchronous motors

Overview of A.C.Motors


1. Synchronous Motors & it's Uses: These motors have the rotor(which is connected to the load) rotating at the same speed as the speed of rotation of the stator current. In other words, we can say these motors don't have slip with respect to the stator current. They are sometimes used no to drive the load but instead act as "synchronous condenser", to improve the power factor of the local grid to which it is connected to. These kind of motors are used even in high precision positioning devices like modern robots.They can also act as stepper motors.

2. Asynchronous Motors & it's Uses: The most common form of motor which is used in everyday life from pumping water up the overhead tank to power plant boiler feed pumps, these kind of motors rule. These motors are very flexible to use and matches the load demand almost for everything. The most widely used

electric car motor

Induction Motors are very important for many industries due to their load bearing capacity and flexibility. These motors,unlike synchronous motors, slip when compared to the stator current field. They are generally used for various types of pumps, compressors and acts as prime movers for many machineries.

3. Single & Three Phase Motors and their Uses: The A.C.Motors can find their usage in 2 forms based on their power supply. The single phase motors are generally found their use in low power requirements/domestic appliances like ceiling fans, mixer grinders, portable power tools etc. The three phase motors are generally found for high power requirements like power drives for compressors, hydraulic pumps, air conditioning compressors, irrigation pumps and many more.


4. Constant, Variable & Adjustable Speed Motors: As already said, A.C.Motors are highly flexible in many ways including their speed control. There are motors which should be run at a constant speed for air compressors. Certain cooling water pumps driven by a.c.motors can be run at two or three speeds by just switching the number of poles used. If the number of poles are changed then the speed also changes. These serve best for sea water cooling pumps in marine engine room applications & many power plants. The speed of the motors can also be varied continuously by some electronic arrangements thus this can be suited for certain applications like a ship's cargo pump, whose discharge rate has to lowered as per the terminals requirement.

5. Varied Structure Motors: These types of motors have different outer cage arrangements, depending upon the usage or any special industrial requirement. For motors used in gas and oil terminals, the casing must be of intrinsically safe, thus it may either have a enclosed casing or a pipe ventilated arrangement such that the sparks produced inside the motor does not cause a fire outside it. Also many motors are totally enclosed as it may be open to weather like those used in hydro-electric power plants.

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content credits:

Electrical machines by A.K. & B.L. Theraja.