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electrical test 3 - theory > Electrical test 3 > Flashcards

Electrical test 3 Flashcards

1
Q

What is the main function of a generator

A

Converts mechanical energy to electrical energy

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2
Q

What happens when a conductor (wire) is moved through a magnetic field?

A

A voltage is induced in the wire

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3
Q

What changes if the wire is moved faster

A

A higher voltage is induced

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4
Q

What changes if the wire is on the opposite direction

A

The polarity of the voltage reverses

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5
Q

What changes if the wire is moved through a stronger magnetic field

A

A higher voltage is induced

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6
Q

For a single loop generator with slip rings what is the general shape of the output waveform

A

Sine wave. Positive & negative

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7
Q

What happens if we replace the slip rings with a commutator

A

Sinusoidal impulses but one polarity only

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8
Q

How is the output affected if we add more turns of wire to the windings

A

A higher output voltage

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9
Q

How is the output affected if we add another winding perpendicular to the first

A

Less ripple in the outlet voltage

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10
Q

The generated voltage is at its peak when the winding is

A

At the edge of the pole face, in the center of the pole face

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11
Q

Why does a shunt field winding have many turns of small diameter wire

A

Wire resistance is the only thing that limits the current

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12
Q

Why is a series resistance sometimes used with the field of a generator

A

To control the output voltage by adjusting the field current

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13
Q

What happens to output voltage if the field resistance is increased? Why?

A

It decrease because the output voltage is proportional to the field strength

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14
Q

What does an electronic voltage regulator do if the generators output voltage is too low

A

Increases the field current

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15
Q

What is counter torque & under What conditions is it strongest

A

Torque that opposes the rotation of the generator when it is feeding current to a load. It is strongest when output current is highest

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16
Q

What is the main difference between generator & an Altnerator

A

Alternator - produces a 3 phase AC output which is then rectified to get DC
Generator - uses a commutator to produce DC

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17
Q

What are two advantages of alternators over generators

A

Better power to weight ratio, no brushes to maintain, better performance at low rpms

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18
Q

What is the main function of of an electric motor

A

Converts electric power to mechanical power

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19
Q

What happens to motor torque if we increase armature current

A

Increase

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20
Q

What happens to motor torque if we Decrease the number of turns in the armature windings

A

Decrease

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21
Q

What happens to motor torque if we Add more armature windings

A

Makes torque smoother

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22
Q

What happens to motor torque if we decrease the field current

A

Decrease

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23
Q

What is the function of a motors commutator

A

Keeps the current flowing in the right direction in the armature windings as it rotates

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24
Q

With most shunt wound motors how much less is the speed at full load than at no load

25
Why does armature current decrease as a motor accelerates up to speed from a standstill
It decreases because CMEF increases with speed & opposes The supply voltage
26
What happens to generated voltage of a generator if we weaken the generators field
Decreases
27
What happens to generated voltage of a generator if we Increases the generators speed
Increases
28
What happens to generated voltage of a generator if we Reduce the number of turns in the armature windings
Decrease
29
What Happens step by step if a motor is running unloaded & then Load is suddenly applied
Load torque increases — motor slows down — Ec decreases — IA increases — torque increases. This continues until the motor slows down enough that the motors torque equals the load torque requirement
30
What are two ways to reverse the direction of the motor
Reverse the armature connections or the field connections but not both
31
What is the rotating part of a 3 phase motor
Rotor
32
What are two common types of 3 phase motors
Induction & synchronous Motors
33
Would a 2 pole motor run faster or slower than a 4 pole motor
Faster
34
The rotor at of a 3 phase induction motor has
Windings & slip rings, windings & a Commutator, cast aluminum bars & slip Rings, cast aluminum bars but no slip rings
35
To produce torque to drive a load an induction motors rotor must turn
Slower than synchronous speed, at synchronous speed, faster than synchronous speed
36
What happens if the torque required by the load exceeds the motor peak torque
The motor stops
37
What happens if the load torque is moderately higher than the motors rated torque
The motors circuit breaker or fuse will blow after a delay to prevent the motor of overheating
38
The rotor of a 3 phase synchronous motor has
Windings & slip Rings, windings & commutator, cast aluminum bars & slip Rings, cast aluminum bars & no Slip rings
39
How fast does a 2 pole synchronous motor turn at full load
24,000rpm it turns at synchronous speed while an induction motor would be slightly slower
40
How does a current get back from loads to the negative terminal of the battery
Through the aluminum airframe
41
How does a voltage regulator control the generator or alternators voltage
Monitors bus voltage, if it's too low VR increases alt field current. If too high VR decreases alt field current
42
Difference between in connections between positive side nd negative side switched master solenoid
Positive side - switch is between coil & + Negative side - switch is between coil & airframe
43
What load usually takes the most current in a small aircraft's electrical system
Starter
44
When a circuit breaker has a bimetal thermal element how does the over current trip mechanism work
Current flowing through bimetal strip heats it up. Strips bends & releases Trip mechanism to open circuit
45
If you ever have to replace a circuit breaker or fuse what are the three rating that must be matched
Voltage, trip current, interpreting capacity
46
What is the main disadvantage of a fuse compared to a circuit breaker
Can't be rest
47
What kinds of loads should be protected with an ANL fuse
Loads with a high irrush current eg lamps & motors
48
An aircraft uses seven 10A fuses, two 20A fuses & one 30A fuse. How many of each rating must be carried on the aircraft
4x10A, 1x20A, 1x30A
49
two situations that can cause an electrical fault
- wire coming loose & touching The airframe - insulation wearing through allowing conductor to touch airframe
50
What physical characteristic of a relay or solenoid limits its current capacity
Physical size of contacts
51
In a voltaic cells the electrode that attracts electrons more strongly will become the ____ electrode
Negative
52
The positive electrode __ electrons ___ ions in the electrolyte
Gives, to, positive
53
What is the difference between primary & secondary Cells
Secondary cells are rechargeable, primary are not
54
Why are NiMH cells preferable over NiCd cells
No memory effect
55
What is the difference between a cell & a battery
A battery is a series of cells connected together
56
Connecting batteries in a series increases ___
Voltage
57
Why does an aircraft lead-acid battery have such a high current capacity
To give the starter the current it needs especially on a cold day
58
Connecting batteries in a parallel increases___
Current capacity

electrical test 3 - theory (1 decks)

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