Do AC induction motors have brushes?

Do AC induction motors have brushes?

• A. Yes
• B. No
• C. Sometimes
• D. Only on rare occasions

Answer: (B)

AC induction motors are brushless by design. The stator creates a rotating magnetic field and the rotor currents are induced by this field, so there’s no need for a direct electrical connection to the rotor or for brushes to commutate. In the most common type, the rotor is a squirrel-cage made of bars shorted by end rings, which lets current flow inside the rotor without any external contact. The only time brushes appear is in the rarer wound-rotor design, where rotor windings are accessed via slip rings and brushes to insert external resistance. So, for the typical AC induction motor, there are no brushes.

AC induction motors are brushless by design. The stator creates a rotating magnetic field and the rotor currents are induced by this field, so there’s no need for a direct electrical connection to the rotor or for brushes to commutate. In the most common type, the rotor is a squirrel-cage made of bars shorted by end rings, which lets current flow inside the rotor without any external contact. The only time brushes appear is in the rarer wound-rotor design, where rotor windings are accessed via slip rings and brushes to insert external resistance. So, for the typical AC induction motor, there are no brushes.