Do AC induction motors require brushes to operate?

Do AC induction motors require brushes to operate?

• A. True
• B. False
• C. Sometimes
• D. Only at startup

Answer: (B)

AC induction motors rely on electromagnetic induction between the stator’s rotating magnetic field and the rotor, so they generate torque without any electrical contacts to the rotor. The common squirrel-cage rotor is a closed, short-circuited path, and currents are induced in it by the stator field, producing motion. Brushes are not part of this induction process, and for the usual induction motor they aren’t needed. There is a wound-rotor variant that uses slip rings and brushes to connect external resistors for starting or control, but the motor’s operation still comes from induction, not from brushes. So, brushes are not required for normal operation.

AC induction motors rely on electromagnetic induction between the stator’s rotating magnetic field and the rotor, so they generate torque without any electrical contacts to the rotor. The common squirrel-cage rotor is a closed, short-circuited path, and currents are induced in it by the stator field, producing motion. Brushes are not part of this induction process, and for the usual induction motor they aren’t needed. There is a wound-rotor variant that uses slip rings and brushes to connect external resistors for starting or control, but the motor’s operation still comes from induction, not from brushes. So, brushes are not required for normal operation.