What is a Rotor : Construction, Working and Its Types

The electromagnetic rotation is the first rotary machine and it was designed by “Ányos Jedlik” from 1826 to 1827 with the help of a commutator as well as electromagnets. In the motor or generator, both the parts like rotor and stator play a key role. The main disparity between these two is that the stator is an inactive part of the motor whereas the rotor is the rotary part. Similarly, asynchronous motors like induction and synchronous motors like alternators and generators include an electromagnetic system that includes a stator as well as a rotor. In an induction motor, there are two types of designs available like squirrel-cage & wound. In alternators and generators, there are two types of designs available like salient pole otherwise cylindrical. This article discusses an overview of the rotor in the motor/generator.

What is the Rotor?

Definition: It is the moving part in an electromagnetic system of the motor, generator and an alternator. It is also called as the Flywheel, rotating magnetic core, an alternator. In an alternator, it includes permanent magnets that move approximately to the iron plates of the stator to produce an AC (Alternating Current). It uses existing motion for its function. The rotation of this can be occurred because of the interaction between magnetic fields & the windings which generate torque in the region of the axis.


Construction and Working Principle of a Rotor

In a three-phase induction motor, once an AC is applied to the rotor then the windings of stator strengthen to generate a rotary magnetic flux. The flux generates a magnetic field in the air gap among the stator & the rotor to induce a voltage for generating the current throughout the bars. The circuit of this can be shorted & the flow of current will be in the conductors.


The act of the rotary flux & the current generates a force to generate a torque to begin the motor. The rotor in an alternator can be designed with a wire coil enclosed in the region of an iron core.

The magnetic component of this can be made with the laminations of the steel to assist stamping conductor slot to exact sizes & shapes. Whenever the current travels in the coil in a magnetic field then it creates a field current in the region of the core.


The strength of the field current mainly controls the level of power in the magnetic field. DC (direct current) drives the field current in the direction of the wire coil through a set of slip rings & brushes.


Similar to any magnet, the magnetic field generated will include two poles like south & north. The direction of the motor in the clockwise can be controlled through the magnets & magnetic fields fixed in this design, which allows the motor to run in a counterclockwise direction.

Types of Rotor

These are classified into different types like Rigid type, Salient pole type, Squirrel cage type, Air type, Wound type. Some of them are explained below.

Rigid Rotor

It is a mechanical type of rotating system. The rotor like an arbitrary can be a three-dimensional rigid device. It can be adjusted in space by using three angles called Euler angles. The linear type is a special rigid type that uses simply two angles to explain. For example, in the diatomic molecule, there are many general molecules that are there with three-dimensional like water ammonia or methane. Here water is asymmetric type, ammonia is the symmetric type, and otherwise, methane is a spherical type.

Squirrel-cage Rotor

It is the rotary part in the squirrel cage induction motor. It is a kind of AC motor. It includes steel laminations with a cylinder shape. The conductors like copper otherwise aluminum are fixed on its surface

Wound Rotor

It is a cylindrical core type, designed with steel lamination includes slots for holding the wires that are equally spaced at 1200 separately & allied in a Y-configuration. The terminals of these windings are taken out to connect with the three slip rings along with brushes on the shaft.

Brushes on the slip rings permit external 3-phase resistors which are connected in series with the windings to provide the speed control.

The exterior resistances turn into a fraction of the rotor to generate a huge torque while starting the motor. When the motor’s speed increases, then the resistance can be decreased to zero.

Salient Pole Rotor

This includes the number of projected poles arranged on a magnetic wheel. In the construction, the poles can be projected to the outside which is designed with the steel laminations. The winding in this can be provided on the poles which are supported with the help of pole shoes. These types of rotors include the shorter axial length and large diameter. Generally, they are used in electrical machines with 100 RPM-1500 RPM speed range

Difference between Stator and Rotor

The main differences between the stator and rotor include the following.



It is n inactive part of the stator It is the rotary part of the stator
It includes a stator core, outer frame, and winding It includes winding and core
It uses three-phase supply It uses DC supply
The winding arrangement is complex The winding arrangement is simple
Insulation is heavy Insulation is less
Friction loss is high Friction loss is low
Cooling is easy Cooling is difficult


The uses of rotor mainly include

  • Automotive engines
  • Industrial refrigerators
  • Snowblowers
  • In the food industry to supply clean air
  • Medical
  • Sanitary Purposes
  • In silo trucks for pressure units to move dry materials like plastics, granulates, sand, cement, lime, silicate & flour.


1). What is the rotor?

It is a rotating part of the motor.

2). What are the types of the rotor?

They are rigid, salient pole, squirrel cage, air, and wound

3). What are the main parts of the rotor?

They are stator core, outer frame, and winding

4). The supply used in the rotor is?

The supply used in this is 3- phase supply

Thus, this is all about an overview of what is a rotor, construction, working principle, different types, and differences. Here is a question for you, what are the functions of a rotor?