What classifies an induction motor?

An induction motor is classified primarily by the way its rotor is set in motion. In an induction motor, the rotor does not have any direct electrical connection to the power supply; instead, it relies on electromagnetic induction to generate the magnetic field necessary for rotation. This process involves creating a rotating magnetic field in the stator, which induces a current in the rotor, causing it to turn. This key characteristic distinguishes induction motors from other types of motors, which may rely on direct electrical connections or mechanical commutation methods.

The other options describe features that do not apply to induction motors. For instance, the use of brushes for commutation is characteristic of DC motors, specifically brushed DC motors, where brushes are used to maintain electrical contact with the rotating armature. While variable frequency drives are often employed with induction motors to control speed and torque, they are not a defining characteristic. Additionally, classifying an induction motor as a direct current motor is incorrect, as induction motors operate on alternating current (AC).