Motors Sample Questions

1. A servo motor has the following parameters:

Assuming the motor accelerates at 3000 rad/sec² up to a final speed of 3000 rpm, what is the minimum amplifier voltage needed?

1. 53 volts
2. 50 volts
3. 47 volts
4. 56 volts
5. none of the above

2. An AC motor with flux vector control can be used to generate a constant speed-torque profile (which means less torque at high speeds and less torque at low speeds). Which of the following statements is true?

1. The motor will run fastest at zero torque
2. The motor will deliver most of the torque at zero speed.
3. The motor can operate efficiently only on a limited range of speeds.
4. The motor will be most efficient at 3240 rpm.
5. The motor will be equally efficient within the constant horsepower region.

3. Which type of motor purposely uses the eddy current phenomenon to generate torque?

1. AC induction motor
2. switched (variable) reluctance motor
3. permanent magnet brushless motor
4. hybrid stepper motor
5. DC brush motor

4. A sales representative, in trying to get you to move to a higher pole-count permanent magnet brushless motor, gives you the following as advantages over an otherwise similar lower pole-count motor.

1. lower iron losses at high speed
2. lower cogging torque
3. lower commutation frequency
4. higher torque at low speeds

Which of these are valid?

1. 2 and 4
2. 1 and 3
3. 1 and 2
4. 3 and 4
5. 1 and 3

5. Stepper motors are used

1. for position control requiring small torque
2. only for open loop applications
3. only for closed loop applications
4. for speed control requiring hign torque
5. in applications that not computer controlled

6. The peak current of a brush motor is generally

1. 2 times its continuous rating
2. equal to its continuous rating
3. 6 times its continuous rating
4. 20 times its continuous rating
5. there is no direct relationship with its continuous rating

7. The peak allowable current of a stepper motor is generally

1. equal to its continuous rating
2. 2 times its continuous rating
3. 6 times its continuous rating
4. 20 times its continuous rating
5. 10 times the continuous rating

8. A servo motor accelerates an inertial load. The system parameters are

Calculate the required current.

1. 20 amps
2. 18 amps
3. 10 amps
4. 40 amps
5. 25 amps

9. Which of the following motors is designed to exploit both the Lorentz torque and reluctance torque principles to achieve a useful output torque?

1. a hybrid stepper motor
2. a switched (variable) reluctance motor
3. a permanent magnet brushless motor
4. an AC induction motor
5. Brushless DC motor

10. What is the key factor limiting the continuous power available from a typical brushless servo motor?

1. the heat dissipation capability of the motor
2. the maximum voltage rating of the motor
3. the maximum current rating of the motor
4. the power rate of the motor
5. the inductance of the motor

11. What do a brushless DC motor and a synchronous AC motor have in common?

1. they are brushless motors
2. they are self commutation motors
3. the angle between the field and the rotor is adjusted automatically
4. the angle between the field and the rotor is the same
5. they are both universal motors

12. What is the major difference between a variable speed switched reluctance motor and a variable speed reluctance motor [that is not switched]?

1. the commutation
2. the number of stator phases
3. the number of pole pieces
4. the orientation of the permanent magnets
5. the armature

13. Using a brushless motor requires

1. electronic commutation
2. a rotor position sensor
3. periodic maintenance
4. brush replacement

1. answers 1, 2
2. answers 1, 3, 4
3. answers 2, 4
4. answers 4
5. answers 1, 2, 3, 4

Page Revised: July 14, 2003