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Test #7 - JATC 2nd Year > AC Theory 3: Lesson 6 - Understanding How The DC Generator Works > Flashcards

AC Theory 3: Lesson 6 - Understanding How The DC Generator Works Flashcards

1
Q

A generator is a device that converts ______ energy into ______ energy.

a. magnetic / electrical
b. magnetic / mechanical
c. mechanical / electrical
d. mechanical / magnetic

A

c. mechanical / electrical

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2
Q

When a conductor cuts magnetic flux lines, a voltage is induced into the conductor.

True or False

A

True

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3
Q

DC generators operate on the principle of electromagnetic induction.

True or False

A

True

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4
Q

According to the left-hand rule for generators, match the correct meaning of the extended digits in the figure.

Center finger: ______
Forefinger: ______
Thumb: ______

Choices:
- Direction of Flux Field
- Direction of Induced Current
- Direction of Motion

A

Center finger: Direction of Induced Current
Forefinger: Direction of Flux Field
Thumb: Direction of Motion

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5
Q

______ voltage is being produced when the rotating conductor is parallel to the magnetic flux lines.

a. One half the maximum
b. The average voltage
c. The maximum
d. Zero

A

d. Zero

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6
Q

Maximum voltage is induced into a conductor when it cuts the magnetic field at ______.

a. 0°
b. 60°
c. 90°
d. 120°

A

c. 90°

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7
Q

______ voltage is induced into the conductor when the loop is at 0°, 180°, and 360° in relation to the field.

a. One half the maximum
b. The average
c. The maximum
d. Zero

A

d. Zero

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8
Q

When a conductor loop is continuously rotated in a magnetic field, the AC output voltage follows the ______ function.

a. cosecant
b. cosine
c. sine
d. tangent

A

c. sine

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9
Q

To convert the AC voltage from the armature to DC voltage, DC generators make use of a(n) ______.

a. armature
b. brush
c. commutator
d. pole piece

A

c. commutator

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10
Q

A ______ causes the AC voltage that is generated to appear as a DC voltage output, because it is a ring constructed of segments separated by insulating material. The connection of the generator loop to these segments is such that the output is always of the same polarity.

a. brush
b. commutator
c. insulator
d. slip ring

A

b. commutator

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11
Q

When AC voltage is generated and then converted to DC voltage by use of a commutator, the voltage output is constant.

True or False

A

False

Note: The voltage is a pulsating DC voltage and is more commonly referred to as ripple voltage.

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12
Q

The frequency of the pulsating DC output voltage of a generator is ______ that of an AC generator.

a. half
b. one-fourth
c. same as
d. twice

A

d. twice

Note: The frequency of output, for the pulsating DC is considered to be twice that of an AC generator because the commutator maintains “+” polarity throughout 360° of rotation, which provides two ripple pulses for one AC cycle.

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13
Q

What is the name of the rotating member of the DC generator?

a. armature
b. brush
c. commutator
d. pole piece

A

a. armature

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14
Q

The ______ are components that make up the armature.

a. commutator
b. iron core
c. windings
d. all of the above

A

d. all of the above

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15
Q

______ is/are a type of armature winding found in generators.

a. Frogleg
b. Lap wound
c. Wave wound
d. All of the above

A

d. All of the above

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16
Q

The wires connected to the brushes of a generator are designated ______ and ______.

a. A1 / A2
b. B1 / B2
c. F1 / F2
d. S1 / S2

A

a. A1 / A2

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17
Q

Select the winding type that completes each statement.

______ wound armatures are probably the most commonly used because they are designed for moderate voltages and moderate currents.
______ wound armatures are used in machines designed for high voltage and low current.
______ wound armatures are used in machines designed for low voltage and high current.

Choices:
- Lap
- Wave
- Frogleg

A

FROGLEG wound armatures are probably the most commonly used because they are designed for moderate voltages and moderate currents.
WAVE wound armatures are used in machines designed for high voltage and low current.
LAP wound armatures are used in machines designed for low voltage and high current.

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18
Q

Which of the following statements are/is a reason brushes are usually made of carbon are:

I. Carbon is softer than copper and allows the brushes rather than the commutator to wear (the latter being more difficult to repair).
II. Carbon withstands the high temperatures that may be present because of arcing and friction.
III. Carbon, copper, and moisture form a very thin, conductive film on the commutator that lubricates and reduces wear.

a. I.
b. II.
c. II. and III.
d. I. and II.
e. I., II., and III.

A

e. I., II., and III.

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19
Q

What is the function of pole pieces installed in the generator housing?

a. To help concentrate the magnetic field
b. To help reduce vibration
c. To help regulate current
d. To help regulate voltage

A

a. To help concentrate the magnetic field

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20
Q

Once the pole pieces are mounted in the generator, the field windings are ______ the pole pieces to form an electromagnet.

a. mounted on
b. placed in
c. wound around

A

c. wound around

21
Q

Permanent magnets are used sometimes as the field poles in small generators.

True or False

A

True

22
Q

What are the two types of connections for generator field windings?

a. Frogleg and lap
b. Series and shunt
c. Wave and lap
d. Wye and delta

A

b. Series and shunt

23
Q

The series field windings are made up of ______ turns with large wire, and the leads are labeled ______ and ______.

a. few / A1 / A2
b. few / S1 / S2
c. many / A1 / A2
d. many / S1 / S2

A

b. few / S1 / S2

24
Q

Shunt field windings are connected in ______ with the armature in a generator, and the leads are tagged ______ and ______.

a. parallel / A1 / A2
b. parallel / F1 / F2
c. parallel / S1 / S2
d. series / F1 / F2

A

b. parallel / F1 / F2

25
Q

The shunt field has a ______ resistance because it is made of ______ wire.

a. high / large
b. high / small
c. low / large
d. low / small

A

b. high / small

26
Q

When a load is connected to a series generator, the output voltage ______.

a. decreases
b. increases

A

b. increases

27
Q

A series generator is self-excited with residual ______.

a. current
b. magnetism
c. power
d. voltage

A

b. magnetism

28
Q

As additional loads are connected to a series generator, the output voltage will continue to ______ until the iron in the pole pieces and armature becomes ______.

a. decrease / reluctant
b. decrease / saturated
c. increase / reluctant
d. increase / saturated

A

d. increase / saturated

29
Q

Which of the factors listed determine the level of the output voltage of a series generator?

I. Number of turns in the armature
II. The strength of the magnetic field at the pole pieces
III. The speed of the cutting action
IV. The direction of rotation

a. I. and II.
b. I., II., and III.
c. I., II., and IV.
d. II. and III.
e. II., III., and IV.

A

b. I., II., and III.

30
Q

Series generators would be best used with a ______ load.

a. constant
b. varying

A

a. constant

31
Q

Self-excited shunt generators make use of ______ to start the generation process.

a. residual current
b. residual magnetism
c. residual power
d. residual voltage

A

b. residual magnetism

32
Q

The shunt type of generator provides ______ output voltage before the load is applied.

a. maximum
b. minimum

A

a. maximum

33
Q

As the load is increased on a shunt type generator, the output voltage will ______.

a. decrease
b. increase

A

a. decrease

34
Q

To control the output voltage of a shunt generator, an electronic voltage regulator is installed to sense changes in the output voltage and makes adjustments to the shunt field current.

True or False

A

True

35
Q

Compound generators make use of a ______ field winding and a ______ field winding.

a. frogleg / lap
b. frogleg / wave
c. lap / wave
d. series / shunt

A

d. series / shunt

36
Q

Compound generators overcome the voltage regulation problems of a series generator, providing good flexibility, voltage regulation, and load control.

True or False

A

True

37
Q

Choose the subdivision of compound generator that completes each statement.

A ______ -shunt compound generator has the shunt field in parallel with the series winding and the armature.

The ______ -shunt compound generator has the shunt field connected in parallel with the armature.

Choices:
- long
- short

A

A LONG -shunt compound generator has the shunt field in parallel with the series winding and the armature.

The SHORT -shunt compound generator has the shunt field connected in parallel with the armature.

38
Q

Select the appropriate term that completes each statement.

A

Cumulative - aid
Differential - oppose

39
Q

Select the appropriate term that completes each statement.

In a flat compound generator, the load voltage is ______ the no-load voltage.
In an over-compound generator, the load voltage is ______ the no-load voltage.
In an under-compound generator, the load voltage is ______ the no-load voltage.

Choices:
- less than
- equal to
- greater than

A

Flat - EQUAL TO
over-compound - GREATER THAN
Under-compound - LESS THAN

40
Q

The greatest generator loss is due to the ______ of the windings.

a. eddy current loss
b. hysteresis loss
c. inductance
d. resistance

A

d. resistance

41
Q

Power loss due to induced currents in the core material of a generator is called ______ loss.

a. eddy current
b. hysteresis
c. inductance
d. resistance

A

a. eddy current

42
Q

______ loss is due to molecular friction.

a. Eddy current
b. Hysteresis
c. Inductance
d. Resistance

A

b. Hysteresis

43
Q

Almost all power losses in a generator, with the exception of flux linkage, are manifested in the form of ______.

a. current loss
b. heat
c. reactance
d. voltage drop

A

b. heat

44
Q

The two primary magnetic flux fields in a generator are field flux and armature flux.

True or False

A

True

45
Q

The magnetic neutral plane will shift in the direction of the ______ rotation.

a. armature
b. field

A

a. armature

Note: See AC Theory textbook, Chapter 13, page 235, Figure 13-20.

46
Q

To prevent a shift in the neutral plane, ______ windings are installed in the generator to cancel the effects of self-induction in the armature.

a. compensating
b. interpole
c. Thomson-Ryan
d. all of the above

A

d. all of the above

47
Q

When DC generators are connected in parallel, an equalizing connection is used to connect the ______ fields of the two machines in ______ with each other.

a. parallel / series
b. series / parallel

A

b. series / parallel

48
Q

If two DC generators are simply connected in parallel without an equalizer connection, one generator will take the load and the second generator will act as a DC motor, drawing current from the first generator.

True or False

A

True

Test #7 - JATC 2nd Year (11 decks)

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