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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
Which factors can be varied in an operating generator?
Flux per pole and rotational speed of the armature
26
What is the effect of generated voltage if the speed of the prime mover is decreased by one-third?
Generated voltage is reduced by one-third
27
Voltage buildup occurs until the generator reaches it’s ___________
No-load terminal voltage
28
Appropriate residual magnetism can be established on the field poles by a process commonly called
Flashing the field
29
The value of field resistance that will limit field current to a value insufficient for voltage buildup is called ________________
Critical field resistance
30
Define armature reaction
Distortion of the main field flux caused by current flowing from the armature to the conductors
31
Interpole winds consist of _______________
Small number of turns of large-gauge wire
32
Interpole coils are connected in ____________
Series with the armature
33
The effects of armature reaction can be minimized by placing windings called __________________ in the main pole faces
Compensating windings
34
List the three types of power loss in a generator
Mechanical Electrical Magnetic
35
Rotational losses include ____________ and ____________
Bearing friction, windage
36
How is the effect of eddy currents minimized in the construction of DC machines?
By laminating the core materials
37
Heat produced by current flowing through the armature and field coils is called ________________
Copper losses
38
Define efficiency
The ratio of power out to power in
39
When referring to Generators, what do A, F and S stand for?
A=Armature F=Shunt field coils S=Series field coils
40
What is flat compound?
Where the terminal voltage is flat or constant with respect to the load
41
What is over compound?
The rise in voltage at the terminals of the generator compensates for the line drop at the load
42
What application is differential compound most commonly used in?
DC arc welding
43
What determines the amount of current that flows through an armature
The impedance of the connected load
44
List the factors that cause a reduction in terminal voltage with increasing load
IR drop of the armature Armature reaction Loss of field current due to a reduction in generated current
45
Is the series generator a practical machine?
No
46
Why would it not be practical to control the output of a series generator with a field rheostat?
The rheostat would have to carry high armature current, resulting in high wattage losses
47
Why is the no-load voltage of a series generator extremely low?
In the absence of a connected load, no current flows through the series coils
48
In a series generator, why does the terminal voltage rise with increasing load?
As armature current increases, the strength of the series field increases
49
Describe how the voltage characteristic of series field coils could be useful
The rising characteristics is used to offset the decrease in terminal voltage associated with shunt field excitation in a compound generator
50
A compound generator contains both _________ and ________ fields
Series, shunt
51
The condition under which the magnetic flux of the series and shunt fields oppose each other is called __________
Differential compound
52
Describe the difference between long shunt and short shunt connections
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
Line drop can be compensated for by using a generator that is ____________
Over compound
53
A compound generator that has a relatively constant terminal voltage characteristic is called _____________
Flat compound
54
What generator has the most severe drop in terminal voltage with load?
Differential compound
55
With respect to long versus short shunt connections, what is a general rule?
Connect the shunt field across the source of emf

Electrical Level 3 (9 decks)

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