Electric motor

What Is the Rotor of an Electric Motor?

The rotor is the component that rotates in an electrical machine. The same definition is valid whether the electric machine is an electric motor or an electric generator.

What is the rotor of an electric motor?

In an electric motor, the rotor works together with the stator (fixed part) to transmit the power of the electric machine.

In addition to being a component of an electric motor, the term is commonly used in rotating machines, such as turbines and centrifugal pumps, as opposed to the so-called stator

How Is the Rotor of an Electrical Machine Formed?

The rotor is composed of a shaft formed by a shaft that supports a set of coils wound on a magnetic core.

This shaft rotates within a magnetic field created either by a magnet, an electromagnet or by passing through another set of coils, wound on pole pieces.

The set of these pole pieces is what is called a stator. The stator remains static and an electric current flows through it. Depending on the motor, the current can be direct current or alternating current.

If the rotor is to be used in medium and high power alternating current machines, they are usually made from sheets of electrical steel. These special sheets help to reduce losses caused by variable magnetic fields such as those generated by the phenomenon of hysteresis or by eddy currents.

Types of Rotors for AC Motors

Electric motors that work with alternating current can work with one of these types of rotors:

  • With pole pieces, this type of rotor is used for synchronous motor or synchronous alternator and pole pieces are obtained by:

    • Permanent magnets, in this case the motor or alternator has a motor shaft with as many pole pairs as the stator pole pairs, regardless of the type of motor (three-phase or single-phase).
      The only exception is in three-phase or two-phase motorcycle alternators, where the alternators are not actual three-phase or two-phase alternators, but are three-phase or two single-phase alternators arranged equidistant, subject to three or two pole pairs. Therefore, there are three or two sinus waves that are not out of phase.

    • Electromagnets, these electromagnets are powered according to the three-phase or single-phase motor / alternator through the three-phase or single-phase network and these expansions must be one per phase and per polar pair (therefore, in the case of a three-phase bipolar phase alternator there are three electromagnets, in the case of a three-phase four-pole alternator there are six electromagnets).

Types of Rotors for DC Motors

The rotor of universal or direct current motors can be:

  • Permanent magnets; System used by brushless motor and stepper motor

  • Winding; System used by almost all direct current motors and universal motors, the different coils are excited in a certain order by means of a brush collector.


    Published: November 13, 2017
    Last review: November 12, 2021