Module 5

(NEETS) MODULE 5

GENERATORS & MOTORS

1. In generators, what principle is used to convert mechanical motion to electrical energy? A. Atomic reaction B. Electrical attraction C. Magnetic repulsion D. Magnetic induction * 2. When you use the left-hand rule for generators, what is indicated by the middle finger? A. Direction of flux B. Direction of motion C. Direction of current flow * D. Direction of the magnetic field 3. The output voltage of an elementary generator is coupled from the armature to the brushes by what devices? A. Slip rings * B. Interpoles C. Terminals D. Pigtails 4. An elementary generator consists of a single coil rotating in a magnetic field. Why is NO voltage induced in the coil as it passes through the neutral plane? A. Flux lines are too dense B. Flux lines are not being cut * C. Flux lines are not present D. Flux lines are being cut in the wrong direction 5. What components cause(s) a generator to produce a dc voltage instead of an ac voltage at its output? A. The brushes B. The armature C. The slip rings D. The commutator * 6. When two adjacent segments of the commutator on a singleloop dc generator come in contact with the brush at the same time, which of the following conditions will occur? A. The output voltage will be zero * B. The output voltage will be maximum negative C. The output voltage will be maximum positive 7. In an elementary, single-coil, dc generator with one pair of poles, what is the maximum number of pulsations produced in one revolution? A. One B. Two * C. Three D. Four 8. If an elementary dc generator has a two coil armature and four field poles, what is the total number of segments required in the commutator? A. 8 B. 2 C. 16 D. 4 * 9. How can you vary the strength of the magnetic field in a dc generator? A. By varying the armature current B. By varying the speed of armature rotation C. By varying the voltage voltage applied to the the electromagnetic electromagnetic field coils * D. By varying the polarity polarity of the the field poles 10. Under Under which of the following conditions does sparking occur between the brushes and the commutator? A. When operating under normal conditions B. When there is improper commutation * C. When there is an an excessive excessive load current current D. When commutation is in the neutral plane

ASSIGNMENT 2

B. Mutual reaction C. Armature reaction * D. Mutual induction 12. Distortion Distortion of the main field by interaction with the armature field can be compensated for by the use of A. slip rings B. interpoles * C. a commutator D. special brushes 13. Motor Motor reaction in a dc generator is a physical force caused by the magnetic interaction between the armature and the field. What effect, if any, does this force have on the operation of the generator? A. It tends to oppose the rotation of the armature * B. It tends to aid the rotation of the armature C.It causes the generator to vibrate D. None 14. In dc generators, copper losses are caused by which of the following factors? A. Reluctance in the field poles B. Resistance in the armature winding * C. Reactance in the the armature and field field windings D. All of the above above 15. Eddy Eddy currents in armature cores are kept low by which of the following actions? A. Using powdered powdered iron as a core material material B. Limiting armature current C. Insulating the core D. Laminating the iron in the core * 16. What makes the drum-type armature more efficient than the Gramme-ring armature? A. The drum-type armature has more windings windings than the the Gramme-ring armature B. The drum-type armature can be rotated rotated faster than the Gramme-ring armature C. The drum-type armature armature coils are fully exposed to the magnetic field, while the Gramme-ring armature coils are only partially exposed to the magnetic field * D. The drum-type armature has laminated laminated core, while the Gramme-ring armature has a solid core 17. What type of dc generator application best utilizes the features of the lapwound armature? A. High-voltage B. High-current * C. High-speed D. Variable-speed 18. Which Which of the following is NOT a major classification of dc generators? A. Compound-wound B. Series-wound C. Shunt-wound D. Lap-wound * 19. What characteristic characteristic of series-wound generators makes them unsuitable for most applications? A. They require external field excitation B. The output voltage varies as the the speed speed varies varies C. They are not not capable capable of supplying heavy loads D. The output output voltage voltage varies varies as the load load current varies * 20. As the load current of a dc generator varies from no-load to full-load, the variation in output voltage is expressed as a percent of the full-load voltage. What term applies to this expression? A. Gain B. Voltage control C.Voltage regulation * D.Load limit

11. Distortion Distortion of the main field by interaction with the armature field defines what term? A. Commutation

1

(NEETS) MODULE 5

GENERATORS & MOTORS

21. When two or more generators are used to supply a common load, what term is applied to this method of operation? A. Series B. Compound C. Split-load D. Parallel * 22. What special-purpose dc generator is used as a high-gain power amplifier? A. Lap-wound B. Shunt-wound C. Amplidyne * D. Compound-connected 23. The gain of an amplifying device can be determined by which of the following formulas? A. GAIN = INPUT + OUTPUT B. GAIN = INPUT x OUTPUT C. GAIN = OUTPUT - INPUT D. GAIN = OUTPUT / INPUT * 24. The maximum gain possible from an amplidyne is approximately A. 100 B. 5,000 C. 10,000 * D. 50,000 25. What determines the direction of rotation of a dc motor? A. The type of armature B. The method of excitation C. The number of armature coils D. The polarity of armature current and direction of magnetic flux * 26. When you use the right-hand rule for motors, what quantity is indicated by the e xtended forefinger? A. Direction of flux north to south * B. Direction of flux south to north C. Direction of current D. Direction of motion 27. Which, if any, of the following situations is a major electrical difference between a dc motor and a dc generator? A. The armatures are different B. The shunt connections are different C. The dc generator requires a commutator, the dc motor does not D. None of the above *

D.

ASSIGNMENT 2

Variable load, high torque *

33. What is the main advantage of a shunt motor over a series motor? A. A shunt motor develops higher torque at lower speeds than a series motor B. A shunt motor can be operated at higher speeds than a series motor C. A shunt motor draws less current from the source than a series motor D. A shunt motor maintains a more constant speed under varying load conditions than a series motor * 34. How can the direction of rotation be changed in a dc motor? A. Only by reversing the field connections B. Only by reversing the armature connections C. By reversing both the armature connections and the field connections D. By reversing either the armature connections or the field connections * 35. When the voltage applied to the armature of a dc shunt motor is decreased, what happens to the motor speed? A. It becomes uncontrollable B. It decreases * C. It increases D. The motor stops 36. In a dc motor, the neutral plane shifts in what direction as the result of armature reaction? A. Clockwise B. Counterclockwise C. In the direction of rotation D. Opposite the direction of rotation * 37. The current in the interpoles of a dc motor is the same as the A. armature current * B. field current C. total load current D. eddy current 38. In a dc motor, what is the purpose of the resistor placed in series with the armature? A. To counteract armature reaction B. To limit armature current * C. To increase field strength D. To prevent overspeeding

28. In a dc motor, what causes counter emf? A. Improper commutation B. Armature reaction C. Generator action * D. Excessive speed

39. Magnetic induction in an alternator is a result of relative motion between what two elements? A. The rotor and the armature B. The armature and the field * C. The field and the stator D. The rotor and the field

29. In a dc motor, how, if at all, does counter emf affect speed? A. It causes the speed to increase * B. It causes the speed to decrease C. It causes rapid fluctuations of the speed D. It does not affect speed

40. Voltage is induced in what part of an alternator? A. The commutator B. The brushes C. The armature * D. The field

30. What is the load on a dc motor? A. The field current B. The armature current C. The mechanical device the motor moves * D. The total current drawn from the source

41. What are the two basic types of alternators? A. Multiphase and polyphase B. Alternating current and direct current C. Rotating field and rotating armature * D. Series-wound and shunt-wound

31. When a series dc motor is operated without a load, which of the following conditions occurs? A. The armature draws excessive current B. The voltage requirement increases C. The armature will not turn D. The armature speeds out of control *

42. Which of the following alternator types is most widely used? A. Shunt-wound B. Rotating-armature C. Series-wound D. Rotating-field *

32. A dc series motor is best suited for which of the following applications? A. Steady load, low torque B. Variable load, low torque C. Steady load, high torque

43. The purpose of the exciter in an alternator is to A. provide dc field excitation * B. compensate for armature losses C. compensate for counter emf D. counteract armature reaction

2

(NEETS) MODULE 5

GENERATORS & MOTORS

44. An alternator using a gas turbine as a prime mover should have what type of rotor? A. Turbine-driven * B. Salient-pole C. Armature D. Geared

ASSIGNMENT 2

ENL xEFL % 100 C. ENL EFL x100 B.

=

−

D.

ENL 100

EFL

=

=

%

%

45. In alternators with low-speed prime movers, only what type of rotor may be used? A. Geared B. Armature C. Salient-pole * D. Turbine-driven

58. In most alternators, the output voltage is controlled by adjusting the A. rotor speed B. field voltage * C. armature resistance D. electric load

46. Alternators are rated using which of the following terms? A. Volts B. Watts C. Amperes D. Volt-amperes *

59. When alternators are to be operated in parallel, which of the following alternator characteristics must be considered? A. Voltage B. Frequency C. Phase relationship D. All the above *

47. What does the term single-phase mean relative to singlephase alternators? A. All output voltages are in phase with each other * B. The voltage and current are in phase C. The phase angle is constant D. Only one voltage is produced

60. Which of the following motors is/are types of ac motor? A. Series B. Synchronous C. Induction D. All of the above *

48. In a single-phase alternator with multiple armature windings, how must the windings be connected? A. Series * B. Parallel C. Wye D. Delta

61. Which of the following types of motors is widely used to power small appliances? A. Universal * B. Synchronous C. Polyphase D. Compound

49. Needs figure 50. Needs figure 51. Needs figure

62. A universal motor is a special type of A. synchronous motor B. series motor * C. parallel motor D. polyphase motor

52. What determines the phase relationship between the individual output voltages in a multiphase alternator? A. The speed of rotation B. The number of field poles C. The method of connecting the terminals D. The placement of the armature coils * 53. What is the phase relationship between the output voltages of a three-phase alternator? A. In phase B. 60º out of phase C. 90º out of phase D. 120º out of phase * 54. The ac power aboard ship is usually distributed as what voltage? A. 115-volt, three-phase B. 115-volt, single-phase C. 230-volt, single-phase D. 450-volt, three-phase * 55. The output frequency of an alternator is determined by what two factors? A. The number of poles and the number of phases B. The number of poles and the speed of rotation * C. The speed of rotation and the VA rating D. The number of phases and the VA rating

56. A four-pole, single-phase alternator rotating at 1800 rpm will produce what output frequency? A. 60 Hz * B. 400 Hz C. 1800 Hz D. 3600 Hz 57. Which of the following is the correct formula for determining the percent of regulation of an alternator? ENL EFL A. x100 % * EFL −

=

63. The number of pole pairs required to establish a rotating magnetic field in a multiphase motor stator is determined by which of the following factors? A. The magnitude of the voltage B. The magnitude of the current C. The number of phases * D. The size of the motor 64. In a two-phase motor stator, what is the angular displacement between the field poles? A. 0º B. 90º * C. 180º D. 360º 65. Adjacent phase windings of a 3-phase motor stator are what total number of degrees apart? A. 30º B. 90º C. 120º * D. 180º 66. Which of the following types of motors has a constant speed from no load to full load? A. Series B. Synchronous* C. Induction D. Universal 67. What type of ac motor is the simplest and least expensive to manufacture? A. Induction * B. Series C. Synchronous D. Two-phase 68. What term applies to the difference between t he speed of the rotating stator field and the rotor speed? A. Slip * B. Synchronous

3

(NEETS) MODULE 5

GENERATORS & MOTORS

ASSIGNMENT 2

C. Rotor error D. Torque 69. The speed of the rotor of an induction motor depends upon which of the following factors? A. The method of connecting the load B. The dc voltage applied to the rotor C. The torque requirements of the load * D. The current in the rotor 70. What type of ac motor is most widely used? A. Series B. Universal C. Synchronous D. Single-phase induction * 71. What type of ac motor uses a combination of inductance and capacitance to apply out-of-phase currents to the start windings? A. Three-phase B. Series C. Synchronous D. Split-phase induction * 72. Why are shaded-pole motors built only in small sizes? A. They have weak starting torque * B. They are expensive in large sizes C. They are unidirectional D. They require large starting current

4