What are the differences between the rotor and stator of an electric motor?

Stator rotor: two similar words that may sound like a children’s song in your head (Albator!).

But unless you’re a mechanic or an engineering enthusiast, you may not know the differences between these two key parts of an electric motor.

Today is your chance to learn a little more about them in our detailed article.

An aircraft turbine

Stator rotor – what are these parts?

The stator and rotor are the two parts of an electric motor.

The significant difference between these two parts is that the rotor is the rotating part of the motor, whereas the stator is the fixed part of the motor.

The frame, core and winding are the parts of the stator.

The frame supports the stator core and protects the three-phase winding. The stator core carries the rotating magnetic field that induces the three-phase supply.

The rotor is located inside the stator core. The rotor winding is energised by the DC supply. The field winding induces the constant magnetic field in the rotor core.

Stator definition

The stator is the static part of the motor. The main function of the stator is to generate the rotating magnetic field.

The stator core supports and protects the three-phase stator winding.

The high-grade silicon steel stamping forms the core of the stator.

Example of an electric motor stator

Rotor definition

The rotating part of the motor is called the rotor.

The core and winding are the rotor parts. Imagine a hamster wheel and you’ll have the basic principle of a rotor in front of you.

The rotor core consists of a cylindrical iron core.

The core has a semicircular slot on its outer surface where the copper or aluminium conductors are placed.

Stator rotor – How it works

DC electrical machines consist of a stator and a rotor.

The stator generates the rotating magnetic field due to the three-phase power supply, using windings (inductors) or permanent magnets.

The rotor is made up of a set of coils connected to a rotating commutator: this keeps the transverse direction of the rotor’s magnetisation fixed as it rotates.

Thanks to this device, the magnetisations of the rotor and stator are always optimally offset.

This offset generates torque according to the law of maximum flux (a north pole attracts a south pole), causing the rotor to rotate.

Example of an airless pump motor

Below you can see the assembly drawing of the Wagner FineCoat 9500 pump.

The inset on the right shows details of the motor components.

Part number 66 indicates the rotor and part number 68 the stator.

These two parts are designed to fit together and cause the electric motor in this pump to work.

Assembly drawing of the Wagner FineCoat 9500 pump

Stator rotor – Main differences

Here is a summary of the differences between a rotor and a stator:

• The stator is the fixed part of the machine, the rotor is the moving part of the machine.
• The stator core, its winding and the outer frame are the three parts of the stator, while the rotor core and the field winding are the parts of the rotor.
• Three-phase power is supplied to the stator winding, which excites the rotor and sets it in motion.
• The arrangement of the stator winding is more complex than that of the rotor.
• The stator winding is highly insulated because it is subjected to high voltage, whereas the rotor winding has low insulation.
• The size of the stator winding is important for carrying the high current compared with the field winding.
• The stator cooling system is better than that of the rotor, because the stator is stationary.
• The rotor has less pressure drop than the stator because of its low weight.

We hope this article helps you to understand how these two key parts of an electric motor work and the differences between them.

To conclude this article, this video explains and presents the relationship between these parts in images.