What controls motor speed and braking?

• A. Soft starter
• B. Capacitor bank
• C. Variable frequency drive
• D. Thermal limiter

Answer: (C)

Speed control and braking for motors are achieved by changing the electrical drive that powers the motor. A variable frequency drive modifies the frequency (and voltage) of the AC supply to an induction motor, so lowering the frequency slows the motor and raising it speeds it up. It can also ramp changes smoothly for gentle start and stop, and use braking methods (like dynamic braking with a resistor or regenerative braking back to the supply) to decelerate efficiently. This combination of variable speed control and built-in braking is what makes it the best choice for controlling motor speed and stopping behavior.

A soft starter limits voltage during startup to reduce inrush but doesn’t continuously control speed or provide braking. A capacitor bank is for power factor correction or starting torque in some cases, not for regulating speed. A thermal limiter protects the motor from overheating and does not influence speed or braking.