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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

A

About 10%

25
Q

Why does armature current decrease as a motor accelerates up to speed from a standstill

A

It decreases because CMEF increases with speed & opposes The supply voltage

26
Q

What happens to generated voltage of a generator if we weaken the generators field

A

Decreases

27
Q

What happens to generated voltage of a generator if we Increases the generators speed

A

Increases

28
Q

What happens to generated voltage of a generator if we Reduce the number of turns in the armature windings

A

Decrease

29
Q

What Happens step by step if a motor is running unloaded & then Load is suddenly applied

A

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
Q

What are two ways to reverse the direction of the motor

A

Reverse the armature connections or the field connections but not both

31
Q

What is the rotating part of a 3 phase motor

A

Rotor

32
Q

What are two common types of 3 phase motors

A

Induction & synchronous Motors

33
Q

Would a 2 pole motor run faster or slower than a 4 pole motor

A

Faster

34
Q

The rotor at of a 3 phase induction motor has

A

Windings & slip rings, windings & a Commutator, cast aluminum bars & slip Rings, cast aluminum bars but no slip rings

35
Q

To produce torque to drive a load an induction motors rotor must turn

A

Slower than synchronous speed, at synchronous speed, faster than synchronous speed

36
Q

What happens if the torque required by the load exceeds the motor peak torque

A

The motor stops

37
Q

What happens if the load torque is moderately higher than the motors rated torque

A

The motors circuit breaker or fuse will blow after a delay to prevent the motor of overheating

38
Q

The rotor of a 3 phase synchronous motor has

A

Windings & slip Rings, windings & commutator, cast aluminum bars & slip Rings, cast aluminum bars & no Slip rings

39
Q

How fast does a 2 pole synchronous motor turn at full load

A

24,000rpm it turns at synchronous speed while an induction motor would be slightly slower

40
Q

How does a current get back from loads to the negative terminal of the battery

A

Through the aluminum airframe

41
Q

How does a voltage regulator control the generator or alternators voltage

A

Monitors bus voltage, if it’s too low VR increases alt field current. If too high VR decreases alt field current

42
Q

Difference between in connections between positive side nd negative side switched master solenoid

A

Positive side - switch is between coil & +

Negative side - switch is between coil & airframe

43
Q

What load usually takes the most current in a small aircraft’s electrical system

A

Starter

44
Q

When a circuit breaker has a bimetal thermal element how does the over current trip mechanism work

A

Current flowing through bimetal strip heats it up. Strips bends & releases Trip mechanism to open circuit

45
Q

If you ever have to replace a circuit breaker or fuse what are the three rating that must be matched

A

Voltage, trip current, interpreting capacity

46
Q

What is the main disadvantage of a fuse compared to a circuit breaker

A

Can’t be rest

47
Q

What kinds of loads should be protected with an ANL fuse

A

Loads with a high irrush current eg lamps & motors

48
Q

An aircraft uses seven 10A fuses, two 20A fuses & one 30A fuse. How many of each rating must be carried on the aircraft

A

4x10A, 1x20A, 1x30A

49
Q

two situations that can cause an electrical fault

A
  • wire coming loose & touching The airframe
  • insulation wearing through allowing conductor to touch airframe
50
Q

What physical characteristic of a relay or solenoid limits its current capacity

A

Physical size of contacts

51
Q

In a voltaic cells the electrode that attracts electrons more strongly will become the ____ electrode

A

Negative

52
Q

The positive electrode __ electrons ___ ions in the electrolyte

A

Gives, to, positive

53
Q

What is the difference between primary & secondary Cells

A

Secondary cells are rechargeable, primary are not

54
Q

Why are NiMH cells preferable over NiCd cells

A

No memory effect

55
Q

What is the difference between a cell & a battery

A

A battery is a series of cells connected together

56
Q

Connecting batteries in a series increases ___

A

Voltage

57
Q

Why does an aircraft lead-acid battery have such a high current capacity

A

To give the starter the current it needs especially on a cold day

58
Q

Connecting batteries in a parallel increases___

A

Current capacity

electrical test 3 - theory (1 decks)

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