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Module 11 > 11.6 Electrical Power > Flashcards

11.6 Electrical Power Flashcards

1
Q

What type of battery systems are used within aircraft?

A

Negative ground or single wire earth returns system

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2
Q

What do they mean by negative ground/ single wire earth system?

A

Negative terminal of battery is connected directly to the metallic portion of the aircraft structure placing the structure at a negative potential.

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3
Q

What type of electrical system is required on composite aircrafts?

A

two-wire electrical system

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4
Q

What is the purpose of a solenoid/contactor?

A

Remotely control a large current source with a small conductor and switch.

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5
Q

What is the purpose of a freewheeling diode?

A

Eliminate spikes when the master switch is opened and the magnetic field from the coil collapses.

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6
Q

Describe the operation of a free wheeling diode.

A

Allows induced EMF to feed back into itself rather than back into the distribution system.

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7
Q

How is thermal runaway prevented on an aircraft with and without the charger unit.

A

Isolate battery when external DC power is applied, or the battery charger unit automatically disconnects the charging current above a pre-set battery temp.

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8
Q

What indications do aircrafts have with nicad batteries fitted?

A

Battery temperature monitor system and a high temperature warning.

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9
Q

What gassing does lead acid batteries give off when charging?

A

Hydrogen and oxygen.

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10
Q

What methods are there of ventilating the aircraft batteries?

A

System A: neutralising agent in a sump jar
B: typical light aircraft/ ram air.
C: pressurisation system air through non return valve.

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11
Q

What can be done to prevent corrosion on aircraft lugs?

A

Smear lugs with an approved lubricant/ white petroleum jelly for quick disconnects

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12
Q

If there is no inbuilt locking device on quick disconnects what must be done?

A

Lockwired closed with 26 AWG copper wire.

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13
Q

Aircraft batteries must be firmly mounted into?

A

Mounting cradle.

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14
Q

When connecting the aircraft battery always connect which lead first?

A

Positive.

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15
Q

When removing the battery from the aircraft always disconnect which lead first?

A

Negative.

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16
Q

What should be checked before installing the battery?

A

Mounting tray/box in good corrosion free condition, vent and drain lines in good condition/not blocked, neutralising jar is serviceable.

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17
Q

What solution is used to neutralize lead acid batteries?

A

Bi-carb and water

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18
Q

What solution is used to neutralize ni-cad batteries?

A

Chromic acid.

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19
Q

What should you flush acid spills on your skin with?

A

Water only.

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20
Q

A DC alternator produces?

A

AC voltage and uses internal rectifiers to produce a dc output.

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21
Q

On larger aircraft normal DC power is supplied by?

A

Transformer Rectifier Units (TRU’s) 115 V AC to 28 V DC

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22
Q

What are used in emergency power situations?

A

AC generators driven by APU’s or RAT’s

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23
Q

Alternators are classified according to?

A

Voltage, ampereage, phase, power output.

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24
Q

EXAM: What are your four main AC power systems?

A
  1. Left engine driven generator
  2. Right engine driven generator
  3. APU generator or starter generator
  4. External power.
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25
Q

On a turbine aircraft the engine driven generators a driven by?

A

CSD - Constant speed drive and
IDG - Integrated drive generator.

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26
Q

What do generators supply?

A

AC 3 phase 115/200 volts at 400hz

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27
Q

What does a static inverter supply?

A

115V AC.

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28
Q

What does a CSD system consist of?

A
  1. Axial Gear Differential AGD
    2 Fly-weight type governor
  2. Variable delivery hydraulic pump.
  3. Quick attach/detach adapted QAD.
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29
Q

To remove a CSD generator from the aircraft how is this achieved?

A

Release the QAD using one fastener.

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30
Q

What does the IDG system consist of?

A

Both the generator and CSD all in one unit, reduces wight and the size of a traditional two unit system

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31
Q

What electrical sub assemblies make up an IDG?

A
  1. Permanent magnet generator
  2. Exciter generator and rectifier assembly
  3. Main generator.
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32
Q

What should be closely monitored in regards to CSD and IDG’s

A

Oil level monitored periodically using the sight glass.

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33
Q

An IDG system installation consists of?

A
  1. Alternating current generator
  2. hydraulic transmission with mechanical control governing the rotational speed of the alternating current generator.
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34
Q

What is in the governing section of the CSD?

A

spring-biased flyweight operated hydraulic control valve.

35
Q

How is the CSD disconnected and reconnected?

A

Electrically decoupled, to reconnect when engine is stationary pulling out on reset handle until solenoid snaps into position.

36
Q

Emergency generators are normally without exception?

A

Permanent magnet alternators and do not require battery power to function.

37
Q

What provides emergency hydraulic power for the flight control if hydraulic power is lost on both engines?

A

RAT, automatically deployed if both engine driven generators fail.

38
Q

What is the RAT made up of?

A
  1. Hydraulic constant speed motor and AC generator (CSM/G)
  2. Generator Control Unit (CSM/G GCU)
39
Q

Efficient operation of electrical equipment in an aircraft depends on?

A

Maintaining a fixed supply voltage under varying load requirements

40
Q

L4 current widning consists of?

A

few turns of heavy wire.

41
Q

L5 voltage winding consists of?

A

Many turns of fine wire.

42
Q

What is this?

A

Grounded field type solid state voltage regulator

43
Q

What is this?

A

Grounded regulator type solid stage voltage regulator

44
Q

What is this?

A

Carbon pile voltage regulator

45
Q

What is this?

A

Transistorized voltage regulator circuit.

46
Q

What is the order of hierarchy for bus systems?

A
  1. Hot battery bus
  2. Essential DC Bus
  3. AC Bus
  4. AC Essential Bus
  5. AC Non-essential bus
47
Q

Describe Essential DC Bus

A

referred to as Battery bus, connected to hot battery bus via a contactor.

48
Q

Describe AC Bus

A

Fed from respective main generator

49
Q

Describe Essential AC Busses

A

Essential lighting, flight control systems, comms, navs, required to ensure safe flight in emergency,

50
Q

Describe Non essential bus

A

galley power, non essential lightingm low priority electrical,referred to as shed busses or isolation busses.

51
Q

If one generator fails what is used to connect bus1 and bus 2 together?

A

But tie breakers (normally open)

52
Q

If a tied AC bus system is tied it means the AC generators are connected or in parallel what conditions must be met?

A

AC Generators must be matched so their output waveforms are the same.
1.Voltages
2. Frequencies
3. voltages in phase
4. same phase rotation (3 phase)

53
Q

The split system breaker will not close if.

A

if the buses properties are outside the limits of voltage, phase rotation or frequency.

54
Q

Relays are used for?

A

Low-current switching applications

55
Q

The part of the relay attracted by electromagnet to close the contact points is called the?

A

Armature

56
Q

Breaker =?

A

High Current

57
Q

Relays =

A

Low Current Switching

58
Q

Bus tie breakers contain 3 heavy duty contacts which connect three phase power to?

A

generator bus bars where it is distributed to the aircraft loads.

59
Q

What is the job of the Generator circuit breaker?

A
  1. Connect AC gen to bus if serviceable
  2. when gen connected to gen bus, bus tie breaker is tripped therefor ensuring ac loads receive power from only 1 power source.
  3. Isolate generator output from aircraft if fault occurs.
60
Q

Inverts are used to?

A

Convert DC to AC at a frequency of 400hz

61
Q

What is this?

A

Rotary AC inverter

62
Q

What is this?

A

Static inverter

63
Q

What are the advantages of a static inverter?

A

No moving parts, less maintenance, less problems.

64
Q

Label these

A
  1. Filter Network (cleans)
  2. 400hz OSC (square)
  3. Pulse shaper (square)
  4. Power Driver (28-115)
  5. Harmonic filter (cleaner not 400hz)
  6. Output stage & final filter (sine wave)
  7. Voltage current/freq sense (ensures correct voltage and frequency)
65
Q

Static inverters produce?

A

115V single phase alternating current 400 Hz from a 18-30 V DC input

66
Q

Transformers allow the values of AC voltage and current to be changed using?

A

Mutual inductance.

67
Q

Rectifiers typically use what to convert AC to DC?

A

Diodes allowing current flow in only 1 direction.

68
Q

Transformer rectifier units are designed to operate on?

A

3 Phase AC inputs and provide continuous DC output. A star to deltas transformer input and output are 30 degree’s out of phase.

69
Q

A fuse should only be replaced with one of?

A

The same voltage and current rating.

70
Q

What are these?

A

Fuses

71
Q

Describe current limiters

A

2 TIMES THEIR RATED CURRENT, 6 TIMES LONGER TO OPEN THAN A FAST BLOW. High current DC power systems, behaves more like a fusible link rather than fast blow, designed for HARD faults,

72
Q

Advantages of circuit breakers?

A

Can be reset once the fault is found., visual indication.

73
Q

What are the 2 types of circuit breakers?

A

Magnetic and thermal circuit breakers.

74
Q

Thermal circuit breakers use what to trip?

A

bi-metallic strips, contact type switch, mechanical latching mechanism.

75
Q

What is the primary reason why circuit breakers are so close to the bus bar?

A

Protect the wiring run from short circuits which would cause a overload and possible fire.

76
Q

What is the secondary reason for circuit breakers?

A

Protect the component at the end of the wiring.

77
Q

How do you tell a circuit breaker is tripped?

A

Small white band.

78
Q

A non trip free circuit breaker can be? (magnetic-hold in)

A

Reset and/or held on even if an overload or excessive heat condition is present.

79
Q

A trip free (thermal) circuit breaker is a?

A

CB that will trip open even if the operating mechanism is held in the ON position.

80
Q

What must be done when a circuit breaker trips?

A

Isolate the faulty or component and repair it, then reset the circuit breaker.

81
Q

Reverse current circuit breakers are designed to?

A

Remain in the “locked out” condition to ensure complete isolation of a circuit until the fault has been cleared.

82
Q

Describe the Merz protection system.

A

When a fault occurs, an unbalanced condition occurs causing current to flow through the coils of the relays thereby energizing them so as to open the line at each end.

83
Q

On a DC power receptacle what is the smaller pin used for?

A

Interlock sensing and polarity check, in event of plug being withdrawn, the external power relay will de-energize before the main pins are disengaged to prevent arcing.

84
Q

How is an AC external power receptacle identified?

A

by its 6 pins

Module 11 (9 decks)

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