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Putanginang Electrical Science > DC Motor > Flashcards

DC Motor Flashcards

(107 cards)

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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
Consist of a loop of wire placed so that it can be rotated in a stationary magnetic field.
Elementary DC motor
26
_____ 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.
Voltage Sliding contact (brushes)
27
Provide the magnetic field and STATOR.
Pole pieces
28
Loop of wire that rotates through the field and ROTOR.
Armature
29
Usually made of carbon with wires attached to them, ride against the commutator.
Brushes
30
External input voltage is applied _____ these brushes.
Across
31
The coil ends of the armature loops (there are two conductors per turn) are connected to rings. They rotate with the armature.
Split rings/commutator
32
The loop (armature) field is both ____ and _____ by the field from the field poles.
Attracted Repelled
33
The north armature pole is repelled from the _____ and attracted to the right by the _____
North field pole South field pole
34
The south armature pole is repelled from the _____ and attracted to the right by the _____
South field pole North field pole
35
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.
Current Polarity
36
Formula of the power developed by a motor?
P=EcIa P=ΘPNZIa/60a P=2πTN/60
37
Because force is acting on the armature conductors, _____ is developed in the motor.
Torque
38
The torque developed its tendency to produce rotation depends upon two factors.
1. Flux created by the main field poles 2. Current flowing in the armature windings.
39
The load on the motor constitutes the force that tends to opposed the rotation.
Counter torque
40
While a DC motor is running, it acts somewhat like a _____.
DC generator
41
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 _____.
Induced voltage Counter EMF Back EMF
42
The counter EMF cannot be _____ or _____ the voltage applied across the armature terminals. There is no way to avoid the counter EMF.
Equal Greater than
43
At the instant DC motor is started the counter EMF is _____ because the armature is not revolving.
Zero
44
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.
Rises
45
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.
Extremely high
46
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.
Resistance Series
47
As the speed increases resistance may be _____ gradually because counter EMF rises.
Cut out
48
Start-up resistor is connected in _____ with the armature.
Series
49
Effect upon speed and armature current
Loading a motor
50
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)
Slow down
51
The counter EMF is ____ for the reason that counter EMF is proportional to speed.
Decreased
52
Reduction in speed result in an ______ armature current
Increased
53
Increased in armature current leads to an _____ in torque developed by the motor to drive the increased load.
Increased
54
The direction of rotation of a dc motor is depends on the direction of the _____ and direction of _____ in the armature.
Magnetic field Current
55
The connection of either the armature or the field must be reversed but _____.
Not both
56
Double pole, Double throw
Forward 1 shorted 3 and 2 shorted 4 Reversed 5 shorted 3 and 6 shorted 4
57
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.
Backward Forward
58
Three way to address the armature reaction in motor.
1. Brush repositioning 2. Compensating windings 3. Interpoles
59
The brushes must be shifted to a new plane.
Brush repositioning
60
Same in motors as they are in generators. They carry the same current as in the armature.
Compensating windings
61
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.
Behind Ahead
62
If compensating windings or inter poles are installed it is not necessarily to ______ when there is an increase or decrease in load.
Shift the brushes
63
The brushes are located on the _____ neutral plane. They remain in that position for all conditions of load.
No load
64
The winding of a gramme-ring armature are place on an _____.
Iron ring
65
The gramme-ring armature is _____ used in modern DC motors.
Seldom
66
The winding on the inside of the ring are shielded from magnetic flux which causes this type of armature to be _____.
Inefficient
67
Each coil is connected to _____. Each coil is in ______ with every other coil.
Two commutator segment Series
68
It is generally used in AC motor, it is identical to the drum winding discussed on DC generator.
Drum type armature
69
This length of each conductor is positioned _____ to the faces of the poles pieces.
Parallel
70
Two general classification of DC motor
1. Separately excited DC motor 2. Self excited DC motor
71
Field winding is energized from a source DC external to the machine called exciter. This type of DC motor is not normally used.
Separately excited DC motor
72
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.
Self excited DC motor
73
Type of self excited DC motor
1. Shunt wound DC motor 2. Series wound DC motor 3. Compound wound DC motor
74
Shunt field motor its field winding also called shunt field winding is connected _____ the armature
Across
75
Series field motor its field winding also called series field winding is connected _____ the armature
Series
76
In shunt motor, torque vs armature current is _____ all through out all load variables. Equal lines in heavy load and light load.
Linear
77
Shunt motor flux is _____ of load.
Independent
78
Under heavy loading the shunt motor will be _____ to develop sufficient torque and will stall.
Unable
79
In series motor, torques vs armature current is _____ at light load variations.
Parabolic
80
In series motor, torques vs armature current is _____ at heavy load variations.
Linear
81
Series motor flux is _____ of load.
Dependent
82
Series motor has _____ overload torque. (Difficult to stall) the speed will become slower but it's ok.
High
83
In compound motor, torques vs armature current is _____ at light load variations.
Curve
84
In compound motor, torques vs armature current is _____ at heavy load variations.
Linear
85
Compound motor flux consists of ____ for shunt and _____ for series
Constant flux Load changing flux
86
Best speed regulations from no load to full load. Speed has a very definite no-load value
Shunt motor
87
Worst speed regulation from no load to full load.
Series motor
88
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.
Run away Belt drive 15%
89
Speed varies considerably. Speed has a very definite no load value.
Compound motor
90
Speed regulation of a motor refers to the _____ that takes place when the load changes.
Speed change
91
T/F The higher the percent of regulation the better the motor.
False Higher > Lower
92
Shunt motors are generally regarded as _____ motors because their percent speed regulation is very small.
Constant speed
93
Compound motors are properly considered to be _____ motors because their percent speed regulation is comparatively high.
Variable speed
94
Series motor certainly has a _____ characteristic their percent speed regulation is very high.
Variable speed
95
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.
8% or less
96
Internal action happens to the motor due to charge in load.
Speed regulation
97
It is imposed action usually through an external adjustment for the purpose of increase or decreasing the speed.
Speed control
98
The speed of a DC motor is change by.
1. Changing the current in the field 2. Changing the current in the armature
99
Speed control can readily be done in one or more of three different ways.
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
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.
Decreased
101
A decrease in field current causes field flux to _____
Decreased
102
Reduction in field strength _____ the counter EMF of the motor since fewer lines are being cut by the armature.
Reduces
103
Reduction of counter EMF an _____ in armature current
Increase
104
Increased in armature current leads to an _____ in torque developed by the motor.
Increased
105
Increase in speed will proportionately ______ counter EMF
Increased
106
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 _____
Constant speed
107

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