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Putanginang Electrical Science > DC Motor > Flashcards

DC Motor Flashcards

1
Q

When an electric generator is in operation. It is driven _____ and develops a _____, which in turn can send a current through a load resistance.

A

Mechanically
Voltage

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2
Q

The load on a generator constitutes those electrical devices that convert _____.

A

Electrical energy into other forms of energy

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3
Q

Examples of load form in generator.

A
  1. Electric lighting
  2. Electric furnaces
  3. Electric welding
  4. Electric motors
  5. Electric battery charging
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4
Q

The voltage of generator can be adjusted by changing the _____ or changing the _____

A

Speed
Strength of magnetic field

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5
Q

The voltage of a generator tends to _____ when the load changes in series and shunt generator.

A

Change

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6
Q

A load increase is always acompanied by drop in _____

A

Terminal voltage

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7
Q

In _____, the voltage may fall (under-compounded), rise (over-compounded) or remain constant (flat compounded) as load changes.

A

Compound generators

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8
Q

The speed of rotation of a generator is usually _____ since the speed of the mechanical prime mover is generally fixed by the governor controls.

A

Constant

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9
Q

Generators can be and frequently are operated in _____ with others to supply power to a common load

A

Parallel

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10
Q

When an electric motor is in operation, it is driven _____ and develops _____ which in turn can produce mechanical rotation.

A

Electrically
Torque

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11
Q

The load on a motor constitutes the force that tends to oppose the rotation.

A

Counter torque

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12
Q

Example of load of motors

A
  1. Fan blades
  2. Pumps
  3. Grinders
  4. Boring mills
  5. Crushers
  6. Excavator
  7. Elevators
  8. Turntables
  9. Churns drills
  10. Food mixer
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13
Q

The speed of rotation of a motor tends to changes as _____ varies.

A

Load

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14
Q

An increase in load caused the speed of a shunt motor to _____, that of a compound motor to _____, and that of a serieis motor to _____.

A

Drop slightly
Drop considerably
Drop very greatly

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15
Q

The speed of rotation of a DC motor can be changed by varying the _____ or changing the _____ across the armature terminals.

A

Strength of magnetic field
Voltage impressed

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16
Q

In motors, the impressed EMF across the motor terminals is usually substantially _____.

A

Constant

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17
Q

Motors usually operate as _____ to drive their individual loads.

A

Single independent units

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18
Q

Machine that converts mechanical energy to electrical energy by using the principle of Lorentz law.

A

Motor

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19
Q

A current-carrying conductor experiences a force when placed in a magnetic field.

A

Lorentz law

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20
Q

When electric current flows through a conductor, it increase a _____ around the conductor.

A

Magnetic field

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21
Q

This _____ interacts with an external magnetic field, by attracting or repelling the magnetism. As a result, the wire experience a force that causes it to jump.

A

Temporary magnetic field

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22
Q

What is the formula of Lorentz force?

A

F = BILsinΘ

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23
Q

A DC motor rotates as a result of _____ interacting with each other, the magnetic field produce by the _____ and the magnetic field produce by the _____.

A

Two magnetic field
Current-carrying armature
Field poles

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24
Q

The direction of the force (or motion of the conductor) can be conveniently obtained using _____.

A

Fleming’s left hand rule

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25
Q

Consist of a loop of wire placed so that it can be rotated in a stationary magnetic field.

A

Elementary DC motor

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26
Q

_____ is applied across the wire so that current flows through it. _____ connect the loop to an external circuit supply in order to pick up the applied EMF.

A

Voltage
Sliding contact (brushes)

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27
Q

Provide the magnetic field and STATOR.

A

Pole pieces

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28
Q

Loop of wire that rotates through the field and ROTOR.

A

Armature

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29
Q

Usually made of carbon with wires attached to them, ride against the commutator.

A

Brushes

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30
Q

External input voltage is applied _____ these brushes.

A

Across

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31
Q

The coil ends of the armature loops (there are two conductors per turn) are connected to rings. They rotate with the armature.

A

Split rings/commutator

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32
Q

The loop (armature) field is both ____ and _____ by the field from the field poles.

A

Attracted
Repelled

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33
Q

The north armature pole is repelled from the _____ and attracted to the right by the _____

A

North field pole
South field pole

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34
Q

The south armature pole is repelled from the _____ and attracted to the right by the _____

A

South field pole
North field pole

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35
Q

After the loop turned far enough so that the north pole is exactly opposite the south pole, this changes the direction of ______ flow through the armature loop and also changes the _____ of the armature field.

A

Current
Polarity

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36
Q

Formula of the power developed by a motor?

A

P=EcIa
P=ΘPNZIa/60a
P=2πTN/60

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37
Q

Because force is acting on the armature conductors, _____ is developed in the motor.

A

Torque

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38
Q

The torque developed its tendency to produce rotation depends upon two factors.

A
  1. Flux created by the main field poles
  2. Current flowing in the armature windings.
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39
Q

The load on the motor constitutes the force that tends to opposed the rotation.

A

Counter torque

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40
Q

While a DC motor is running, it acts somewhat like a _____.

A

DC generator

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41
Q

This _____ causes current to flow in the loop with a direction opposite that of the current caused by the armature supply voltage. This induced voltage is called _____ or _____.

A

Induced voltage
Counter EMF
Back EMF

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42
Q

The counter EMF cannot be _____ or _____ the voltage applied across the armature terminals. There is no way to avoid the counter EMF.

A

Equal
Greater than

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43
Q

At the instant DC motor is started the counter EMF is _____ because the armature is not revolving.

44
Q

As the armature accelerates to full speed the value of counter EMF _____ to a value that causes the proper value of armature current to flow.

45
Q

At the instant DC motor when counter EMF is zeros, the armature current would be _____ unless some resistance were added to the offset the lack of counter EMF.

A

Extremely high

46
Q

During initial start-up when counter EMF is zero, as the motor is coming up to a speed a _____ must be inserted (in _____ with the armature circuit) to take place of counter EMF.

A

Resistance
Series

47
Q

As the speed increases resistance may be _____ gradually because counter EMF rises.

48
Q

Start-up resistor is connected in _____ with the armature.

49
Q

Effect upon speed and armature current

A

Loading a motor

50
Q

When a load is applied to a motor the natural tendency of the latter is to _____ because the opposition of motion (the counter torque) is increased)

51
Q

The counter EMF is ____ for the reason that counter EMF is proportional to speed.

52
Q

Reduction in speed result in an ______ armature current

53
Q

Increased in armature current leads to an _____ in torque developed by the motor to drive the increased load.

54
Q

The direction of rotation of a dc motor is depends on the direction of the _____ and direction of _____ in the armature.

A

Magnetic field
Current

55
Q

The connection of either the armature or the field must be reversed but _____.

56
Q

Double pole, Double throw

A

Forward 1 shorted 3 and 2 shorted 4
Reversed 5 shorted 3 and 6 shorted 4

57
Q

The armature field distorts the flux between pole pieces, as a result the neutral plane is shifted _____ in the direction opposite that of rotation. This is different from a DC generator where the neutral plane is shifted _____ in the direction of rotation.

A

Backward
Forward

58
Q

Three way to address the armature reaction in motor.

A
  1. Brush repositioning
  2. Compensating windings
  3. Interpoles
59
Q

The brushes must be shifted to a new plane.

A

Brush repositioning

60
Q

Same in motors as they are in generators. They carry the same current as in the armature.

A

Compensating windings

61
Q

Inter poles in a motor are wound and placed so that each has the same magnetic polarity as the main pole _____ it, in the direction opposite of rotation. Unlike in generator the the main pole is _____ of it in the direction of rotation.

A

Behind
Ahead

62
Q

If compensating windings or inter poles are installed it is not necessarily to ______ when there is an increase or decrease in load.

A

Shift the brushes

63
Q

The brushes are located on the _____ neutral plane. They remain in that position for all conditions of load.

64
Q

The winding of a gramme-ring armature are place on an _____.

65
Q

The gramme-ring armature is _____ used in modern DC motors.

66
Q

The winding on the inside of the ring are shielded from magnetic flux which causes this type of armature to be _____.

A

Inefficient

67
Q

Each coil is connected to _____. Each coil is in ______ with every other coil.

A

Two commutator segment
Series

68
Q

It is generally used in AC motor, it is identical to the drum winding discussed on DC generator.

A

Drum type armature

69
Q

This length of each conductor is positioned _____ to the faces of the poles pieces.

70
Q

Two general classification of DC motor

A
  1. Separately excited DC motor
  2. Self excited DC motor
71
Q

Field winding is energized from a source DC external to the machine called exciter. This type of DC motor is not normally used.

A

Separately excited DC motor

72
Q

Field winding is energized by its own armature possible only if the field pole pieces have retained a slight amount of permanent magnetism called remanent/residual magnetism.

A

Self excited DC motor

73
Q

Type of self excited DC motor

A
  1. Shunt wound DC motor
  2. Series wound DC motor
  3. Compound wound DC motor
74
Q

Shunt field motor its field winding also called shunt field winding is connected _____ the armature

75
Q

Series field motor its field winding also called series field winding is connected _____ the armature

76
Q

In shunt motor, torque vs armature current is _____ all through out all load variables. Equal lines in heavy load and light load.

77
Q

Shunt motor flux is _____ of load.

A

Independent

78
Q

Under heavy loading the shunt motor will be _____ to develop sufficient torque and will stall.

79
Q

In series motor, torques vs armature current is _____ at light load variations.

80
Q

In series motor, torques vs armature current is _____ at heavy load variations.

81
Q

Series motor flux is _____ of load.

82
Q

Series motor has _____ overload torque. (Difficult to stall) the speed will become slower but it’s ok.

83
Q

In compound motor, torques vs armature current is _____ at light load variations.

84
Q

In compound motor, torques vs armature current is _____ at heavy load variations.

85
Q

Compound motor flux consists of ____ for shunt and _____ for series

A

Constant flux
Load changing flux

86
Q

Best speed regulations from no load to full load. Speed has a very definite no-load value

A

Shunt motor

87
Q

Worst speed regulation from no load to full load.

A

Series motor

88
Q

Series motor tends to _____ at light load - it should never be used _____ or when the load is such that torque might drop approximately _____ of the full load torque.

A

Run away
Belt drive
15%

89
Q

Speed varies considerably. Speed has a very definite no load value.

A

Compound motor

90
Q

Speed regulation of a motor refers to the _____ that takes place when the load changes.

A

Speed change

91
Q

T/F
The higher the percent of regulation the better the motor.

A

False
Higher > Lower

92
Q

Shunt motors are generally regarded as _____ motors because their percent speed regulation is very small.

A

Constant speed

93
Q

Compound motors are properly considered to be _____ motors because their percent speed regulation is comparatively high.

A

Variable speed

94
Q

Series motor certainly has a _____ characteristic their percent speed regulation is very high.

A

Variable speed

95
Q

If a change from no mechanical load to full load cause the speed to drop approximately _____ the motor is said to be of constant-speed type.

A

8% or less

96
Q

Internal action happens to the motor due to charge in load.

A

Speed regulation

97
Q

It is imposed action usually through an external adjustment for the purpose of increase or decreasing the speed.

A

Speed control

98
Q

The speed of a DC motor is change by.

A
  1. Changing the current in the field
  2. Changing the current in the armature
99
Q

Speed control can readily be done in one or more of three different ways.

A
  1. Inserting a field rheostat in series with shunt field circuit
  2. Inserting a resistance in series with the armature circuit
  3. Varying the voltage across the armature circuit
100
Q

For a constant applied voltage as the resistance of the rheostat is increased, the amount of current through the field _____ according to ohm’s law.

101
Q

A decrease in field current causes field flux to _____

102
Q

Reduction in field strength _____ the counter EMF of the motor since fewer lines are being cut by the armature.

103
Q

Reduction of counter EMF an _____ in armature current

104
Q

Increased in armature current leads to an _____ in torque developed by the motor.

105
Q

Increase in speed will proportionately ______ counter EMF

106
Q

The speed and counter EMF will then continue to increase until the armature current and torque are reduced to values just large enough to supply the load at a new _____

A

Constant speed

Putanginang Electrical Science (1 decks)

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