Industrial DC Motors: Summary of Units 1-3

OBJECTIVE

To give the learner an opportunity to evaluate the knowledge and understanding acquired in the study of the previous three units.

Select the correct answer for each of the following statements.

1. The twisting effect of a motor shaft is called its:

a. turning power. c. r/min.

b. horsepower. d. torque.

2. The twisting effect of a dc motor is produced primarily by:

a. the armature.

b. the rotor.

c. a current-carrying conductor in a magnetic field.

d. torque in the field coils.

3. A dc motor is required to maintain the same speed at no load and full load. This type of operation can only be obtained by using a:

a. series motor. c. differential compound-wound motor.

b. shunt motor. d. cumulative compound-wound motor.

4. As a load is applied to a dc shunt motor the:

a. Field current increases.

b. counter emf increases.

c. armature current increases.

d. torque developed decreases.

5. The speed of a dc shunt motor:

a. increases with an increase in load.

b. decreases with an increase in applied voltage.

c. decreases if the field strength is increased.

d. decreases less than a series motor of the same hp for the same increase in load.

6. As load is applied to a dc series motor the:

a. Field current decreases.

b. Field voltage increases.

c. armature current decreases.

d. armature voltage increases.

7. The load requirements of a particular dc motor installation require extremely high starting torque. If speed regulation isn't important, use a:

a. series motor.

b. shunt motor.

c. differential compound-wound motor. d. cumulative compound-wound motor.

8. As a load is applied to a cumulative compound-wound dc motor its:

a. speed decreases.

b. counter emf decreases.

c. torque decreases.

d. series field current decreases.

9. In a cumulative compound-wound dc motor, the a. series winding develops the major part of the total flux.

b. series and shunt windings develop field flux in the same direction.

c. shunt winding must be connected across the brushes.

d. series windings don't pass the shunt field current.

10. In a dc shunt motor all but one of the following are true.

a. Torque is proportional to the field current.

b. The same voltage is applied to armature and field circuits.

c. The no-load speed is controlled by the impressed voltage.

d. The motor is suitable for installations requiring substantially constant speed with variable loading.

11. In a differential compound-wound dc motor:

a. the series and shunt fields establish flux in the same direction.

b. the series winding acts to reduce speed as load is applied.

c. an increase in total current input as the result of loading increases the shunt field current.

d. changes in torque result in change of current in the series field windings.

12. If the direction of field flux and the direction of armature current are changed, the torque developed by the motor is:

a. stronger. c. the same.

b. less. d. reversed.

13. A generator shunt field winding is:

a. high resistance. c. non-inductively wound.

b. low resistance. d. embedded in the armature.

14. For proper operation in a four-lead dc motor, leads S1 and S2 should be connected to A1 and A2 in:

a. parallel. c. shunt.

b. series. d. series-parallel.

15. Decreasing the resistance of a generator field rheostat a. decreases the flux. c. increases the voltage. b. decreases the voltage. d. decreases the speed.

16. A series field, if connected across a motor armature and energized,

a. makes the motor race dangerously.

b. causes a short circuit.

c. creates excessive flux.