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Electrical Level 3 > Line M-3 > Flashcards

Line M-3 Flashcards

1
Q

What is the main difference in construction of a DC generator and a DC motor?

A

The type of enclosure

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2
Q

The rotating part of a DC generator is called ________

A

The rotor/armature

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3
Q

What are the three basic types of armature windings?

A

Frog leg windings
Lap windings
Wave windings

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4
Q

What is the electrical function of the commutator?

A

To maintain the current in one direction to the external circuit

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5
Q

What common materials are used in making brushes?

A

Carbon
Electro-graphite
Graphite
Copper Graphite

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6
Q

Suitable brush pressure is usually between what psi?

A

1 and 2 psi

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7
Q

What is the function of field poles?

A

To provide the necessary magnetic field

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8
Q

What two kinds of bearings do DC machines use?

A

Sleeve or Ball Bearings

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9
Q

Grease nipples in the end of shields indicate that the machine uses what kind of bearings?

A

Open bearings

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10
Q

What is a dynamo?

A

A rotating machine that converts mechanical energy into electrical energy

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11
Q

What applications are frog leg windings used in?

A

Moderate current and moderate voltage applications

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12
Q

What applications are lap windings used in?

A

High current and low voltage applications

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13
Q

What applications are wave windings used in?

A

Low current and high voltage applications

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14
Q

What function do brushes provide?

A

They conduct current to or from the armature coils

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15
Q

What is the purpose of frame and end shields

A

To provide mechanical support for the machine

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16
Q

Which way does the neutral plain shift in a generator?

A

With the generator

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17
Q

Which way does the neutral plain shift in a motor

A

Against the motor

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18
Q

Define Generator

A

A machine that converts mechanical energy into electrical energy

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19
Q

What are magnetos?

A

Small generators that use permanent magnets for excitation

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20
Q

Which two ways are field coils connected in?

A

Series, parallel (shunt)

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21
Q

Which field windings are made of a low number of turns of large gauge wire?

A

Series windings

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22
Q

What device in the shunt field circuit is used to control generator voltage?

A

A rheostat

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23
Q

The buildup of voltage in a self-excited generator requires ______________

A

Residual magnetism

24
Q

What five factors influence generated voltage?

A

Number of poles
Flux per poles
Rotational speed of the armature
Number of paths
Total number of active conductors in the armature

25
Q

Which factors can be varied in an operating generator?

A

Flux per pole and rotational speed of the armature

26
Q

What is the effect of generated voltage if the speed of the prime mover is decreased by one-third?

A

Generated voltage is reduced by one-third

27
Q

Voltage buildup occurs until the generator reaches it’s ___________

A

No-load terminal voltage

28
Q

Appropriate residual magnetism can be established on the field poles by a process commonly called

A

Flashing the field

29
Q

The value of field resistance that will limit field current to a value insufficient for voltage buildup is called ________________

A

Critical field resistance

30
Q

Define armature reaction

A

Distortion of the main field flux caused by current flowing from the armature to the conductors

31
Q

Interpole winds consist of _______________

A

Small number of turns of large-gauge wire

32
Q

Interpole coils are connected in ____________

A

Series with the armature

33
Q

The effects of armature reaction can be minimized by placing windings called __________________ in the main pole faces

A

Compensating windings

34
Q

List the three types of power loss in a generator

A

Mechanical
Electrical
Magnetic

35
Q

Rotational losses include ____________ and ____________

A

Bearing friction, windage

36
Q

How is the effect of eddy currents minimized in the construction of DC machines?

A

By laminating the core materials

37
Q

Heat produced by current flowing through the armature and field coils is called ________________

A

Copper losses

38
Q

Define efficiency

A

The ratio of power out to power in

39
Q

When referring to Generators, what do A, F and S stand for?

A

A=Armature
F=Shunt field coils
S=Series field coils

40
Q

What is flat compound?

A

Where the terminal voltage is flat or constant with respect to the load

41
Q

What is over compound?

A

The rise in voltage at the terminals of the generator compensates for the line drop at the load

42
Q

What application is differential compound most commonly used in?

A

DC arc welding

43
Q

What determines the amount of current that flows through an armature

A

The impedance of the connected load

44
Q

List the factors that cause a reduction in terminal voltage with increasing load

A

IR drop of the armature
Armature reaction
Loss of field current due to a reduction in generated current

45
Q

Is the series generator a practical machine?

A

No

46
Q

Why would it not be practical to control the output of a series generator with a field rheostat?

A

The rheostat would have to carry high armature current, resulting in high wattage losses

47
Q

Why is the no-load voltage of a series generator extremely low?

A

In the absence of a connected load, no current flows through the series coils

48
Q

In a series generator, why does the terminal voltage rise with increasing load?

A

As armature current increases, the strength of the series field increases

49
Q

Describe how the voltage characteristic of series field coils could be useful

A

The rising characteristics is used to offset the decrease in terminal voltage associated with shunt field excitation in a compound generator

50
Q

A compound generator contains both _________ and ________ fields

A

Series, shunt

51
Q

The condition under which the magnetic flux of the series and shunt fields oppose each other is called __________

A

Differential compound

52
Q

Describe the difference between long shunt and short shunt connections

A

In long shunt connections, the shunt field is connected across the line. In short shunt connections, the shunt field is connected across the armature

53
Q

Line drop can be compensated for by using a generator that is ____________

A

Over compound

53
Q

A compound generator that has a relatively constant terminal voltage characteristic is called _____________

A

Flat compound

54
Q

What generator has the most severe drop in terminal voltage with load?

A

Differential compound

55
Q

With respect to long versus short shunt connections, what is a general rule?

A

Connect the shunt field across the source of emf

Electrical Level 3 (9 decks)

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