Which statement about AC drives is true?

Which statement about AC drives is true?

• A. Increase speed without reducing torque
• B. They typically reduce torque when increasing speed
• C. They cannot adjust torque
• D. They only work with DC motors

Answer: (A)

AC drives (variable-frequency drives) control motor speed by varying the supply frequency and voltage to an AC motor. By adjusting these things, the drive can set a higher speed while supplying the torque the load needs. When you keep the same torque demand and raise the speed, the drive can increase current as needed to maintain that torque up to the motor’s base speed, so speed can rise without a drop in torque in the constant-torque region. Beyond base speed, torque typically falls off to keep the motor operating within its power limits, so the relationship changes at higher speeds. The other statements aren’t accurate: torque can be adjusted by the drive, they run on AC motors (not exclusively DC), and they aren’t restricted to DC motors.

AC drives (variable-frequency drives) control motor speed by varying the supply frequency and voltage to an AC motor. By adjusting these things, the drive can set a higher speed while supplying the torque the load needs. When you keep the same torque demand and raise the speed, the drive can increase current as needed to maintain that torque up to the motor’s base speed, so speed can rise without a drop in torque in the constant-torque region. Beyond base speed, torque typically falls off to keep the motor operating within its power limits, so the relationship changes at higher speeds. The other statements aren’t accurate: torque can be adjusted by the drive, they run on AC motors (not exclusively DC), and they aren’t restricted to DC motors.