## VFD(Variable Frequency Drive) Objective type Questions and Answers

11.  Much of the same logic contained in large, powerful VFDs is also embedded in small ________ such as those commonly used in computer fans.
A. Electronic speed control
B. Brushless DC electric motor
C. Induction motor
D. Electric motor
Ans: B

12.  In addition to this simple volts per hertz control more advanced control methods such as vector control and ________ (DTC) exist.
A. Electrical generator
B. Linear motor
C. Direct torque control
D. Electric motor
Ans: C

13.  This starting method typically allows a motor to develop 150% of its rated ________ while the VFD is drawing less than 50% of its rated current from the mains in the low speed range.
A. Torque
B. Energy
C. Force
D. Angular momentum
Ans: A

14. Thus the ________ of volts per hertz must be regulated to a constant value (460/60 = 7.67 V/Hz in this case).
A. Percentage
B. Divisor
C. Ratio
D. Reason
Ans: C

15. A small amount of braking torque is available to help ________ the load a little faster than it would stop if the motor were simply switched off and allowed to coast.
A. Acceleration
B. Kinematics
C. Speed
D. Force
Ans: A

16. Variable Frequency Drives work with which of the following motors?
A. Single-Phase AC Motors
B. Three-Phase AC Motors
C. DC Motors
D. B and C are correct but not A.
E. A, B and C are all correct.
Ans: B

17. The setting for the speed of a VFD is known as which of the following:
A. Setpoint
B. Control Point
C. Reference
D. Speed Point
E. All of the above are common names for the speed setting.
Ans: C

18. Assuming no friction losses, if a VFD is operating a fan at 30Hz, ½ the full speed, which
of the following is the correct power consumption?
A. 50% power consumption
B. 33% power consumption
C. 25% power consumption
D. 12.5% power consumption
E. 6.7% power consumption
Ans: D

19. Limits are very important for a VFD operating a fan. Which of the following are the most commonly used limits for a fan?
A. 18Hz Minimum speed; 60Hz Maximum speed
B. 6Hz Minimum speed; 60Hz Maximum speed
C. 18Hz Minimum speed; 90Hz Maximum speed
D. 6Hz Minimum speed; 90Hz Maximum speed
E. 0Hz Minimum speed; 120Hz Maximum speed
Ans: B

20. Inside the VFD, acceleration, is also known as which of the following:
A. Increase Speed
B. Increase Setpoint
C. Speed UP
D. Run-Up
E. Ramp-Up
Ans: E