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Following dc motors provides the highest starting torque

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Reference no: EM131076574

1. Which of the following DC motors provides the highest starting torque?

A. Series-wound

B. Shunt-wound

C. Compound-wound

D. Generator-wound

2. What is the efficiency of a DC generator that requires 100 watts of energy to supply 80 watts of output power?

A. 8%

B. 12.5%

C. 80%

D. 125%

3. Which of the following DC motors acts as a form of electrical ratchet?

A. Servo

B. Permanent-magnet

C. Stepper

D. Syncro

4. Why is steel alloyed with silicon used as the core material for the armature of a DC generator?

A. To reduce eddy-current flow in the armature core

B. To increase the hysteresis loss in the core

C. To decrease the resistance of the armature conductors

D. To reduce the resistance to current flow in the core

5. Which of the following losses can happen even when a DC generator isn't connected to a load?

A. I2R loss

B. Brush friction loss

C. Copper loss

D. Iron loss

6. If a DC generator with an efficiency of 94% has an output of 240 volts at 100 amperes, the machine power losses for this generator would be

A. 1175 watts.

B. 1487 watts.

C. 1532 watts.

D. 1655 watts.

7. What happens when the speed of a generator's armature increases?

A. The load decreases

B. The field current reverses

C. The windage loss decreases

D. The induced voltage increases

8. To get better commutation in a DC generator, you should move the brushes

A. in the direction of rotation.

B. in the direction of field polarity.

C. against the direction of rotation.

D. against the direction of field strength.

9. Which of the following DC motor drive systems controls motor speed by controlling the period of the waveform to the drive's output transistor?

A. Frequency-effect transition (FET)

B. Frequency-drift commutation (FDC)

C. Pulse-controlled modulation (PCM)

D. Pulse-width modulation (PWM)

10. In a generator, the voltage induced in a rotating armature coil is at maximum when the coil

A. moves parallel with the magnetic lines of force.

B. cuts the fewest magnetic lines of force.

C. is at right angles to the magnetic lines of force.

D. is in a vertical position between the field poles.

11. Which of the following methods can be used to cut down on brush sparking in a DC generator?

A. Install interpoles in the armature core.

B. Install compensating coils in the field pole faces.

C. Move the brushes against the armature rotation.

D. Connect commutating coils in parallel with the armature coils.

12. Technician A is told to inspect and clean the brush holders and replace the brushes in a DC generator. Which of the following areas would the technician be working on in this case?

A. The rear end bell

B. The commutator

C. The rigging

D. The shaft

13. Which of the following devices did older DC motor speed controllers often use to control armature

voltage?

A. A battery

B. A rheostat

C. A potentiometer

D. A diode

14. What is the efficiency of a DC generator that requires 200 watts of energy to supply 160 watts of output power?

A. 40%

B. 80 %

C. 90%

D. 125%

15. In a field weakening DC motor speed controller system, what happens when the voltage to the field is decreased?

A. The motor speed will increase.

B. The motor will slow down.

C. Sparking will occur at the commutator.

D. Excess heat will be generated.

16. What type of generator connection is shown in the diagram below?

A. Separately-excited series-wound

B. Separately-excited shunt-wound

C. Separately-excited compound-wound

D. Self-excited series-wound

17. What part of a motor's armature is in direct contact with the brushes?

A. The interpole

B. The end bell

C. The commutator

D. The case

18. The turning force produced by a motor is called

A. excitation.

B. horsepower.

C. SCR.

D. torque.

19. A DC generator's load loss from hysteresis is one type of

A. bearing friction loss.

B. brush-contact loss.

C. copper loss.

D. iron loss.

20. When using an SCR motor speed controller, the speed of the motor depends upon the

A. voltage on the field windings.

B. resistance in the armature circuit.

C. triggering timing of the SCR.

D. AC input voltage to the rectifier.

21. What type of generator connection is shown in the diagram below?

A. Self-excited compound-wound

B. Self-excited series-wound

C. Separately-excited series-wound

D. Separately-excited compound-wound
22. In which of the following figures is the maximum voltage being induced in the coil?

A.

B, C, and D are inapplicable for maximum voltage.

23. Which of the following types of motors is usually used in machine tools and precision positioning equipment?

A. A series-wound DC motor

B. A DC permanent magnet servo motor

C. A compound-wound DC motor

D. A shunt-wound DC motor

24. If the current in a generator's armature increases from two amps to eight amps, what is the increase in copper losses?

A. Four times

B. Sixteen times

C. Six times

D. Thirty-six times

25. What is the efficiency of a generator that produces 80 kilowatts of electric energy and has electric and mechanical losses of 20 kilowatts?

A. 58.3%

B. 80%

C. 60%

D. 100%

Reference no: EM131076574

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