1
Q
Main uses of electrical power on modern aircraft
A
Heating, lighting, electrically driven actuators, avionics, fly-by-wire, IFE
2
Q
Typical electrical power generation of A380
A
~600 kVA
3
Q
Typical electrical power generation of Boeing 787
A
~1000 kVA
4
Q
Two main subsystems of aircraft electrical power system
A
Generation and distribution
5
Q
Main DC power sources on aircraft
A
Battery, external power, DC generators/TRUs
6
Q
Primary uses of aircraft battery
A
Emergency power, APU start, essential ground power
7
Q
Most common aircraft battery type
A
Nickel-Cadmium (Ni-Cd)
8
Q
Nominal aircraft DC system voltage
A
24 V DC
9
Q
Minimum battery endurance after generator failure
A
At least 30 minutes
10
Q
Ni-Cd cell nominal voltage
A
~1.2 V
11
Q
Ni-Cd cell voltage during charge
A
Up to ~1.5 V
12
Q
Ni-Cd fully discharged cell voltage
A
~1.0 V
13
Q
Main risk of deep Ni-Cd discharge
A
Cell reversal
14
Q
Minimum acceptable battery capacity at overhaul
A
0.8
15
Q
Thermal runaway definition
A
Self-heating condition causing uncontrolled temperature rise
16
Q
Common causes of Ni-Cd thermal runaway
A
Unbalanced cells, impurities, shorts, overcharging
17
Q
Charging method mainly used for Ni-Cd batteries
A
Constant current
18
Q
Charging method mainly used for lead-acid batteries
A
Constant voltage
19
Q
Typical DC bus voltage supplied by TRUs
A
28 V DC
20
Q
Hot battery bus definition
A
Bus permanently energized by battery
21
Q
Function of RCCB
A
Isolates battery to preserve essential loads
22
Q
Neutralising agent for acid spills
A
Bicarbonate of soda
23
Q
Neutralising agent for alkaline spills
A
Boric acid
24
Q
Advantages of lithium-ion aircraft batteries
A
Lightweight, fast charge, high power, no memory effect
25
Safe voltage range of Li-ion cells
~3–4.2 V per cell
26
Primary risk of lithium-ion batteries
Thermal runaway with fire/explosion
27
Typical DC generator output voltage
28 V ± 0.5 V
28
DC generator excitation type
Shunt-field, self-excited
29
Typical large aircraft DC generator rating
28 V, 100–200 A
30
Function of starter-generator
Acts as starter then generator
31
TRU purpose
Convert AC to DC
32
Bus Tie Breaker function
Connects buses during generator failure
33
Parallel DC system purpose
Load sharing and redundancy
34
Essential DC bus purpose
No-break power to critical systems
35
Standard aircraft AC supply
115/200 V, 400 Hz, three-phase
36
Reason for constant frequency AC
Parallel operation and motor compatibility
37
CSD purpose
Maintain constant generator speed
38
IDG definition
Integrated Drive Generator combining CSD and generator
39
Typical IDG output
~115/200 V, 400 Hz, ~90 kVA
40
Function of PMG
Provides self-excitation power
41
Static inverter purpose
Convert DC to AC
42
GCU main functions
Voltage, frequency, protection, load sharing
43
Paralleling requirements (AC)
Voltage, frequency, phase, rotation limits
44
Real load sharing control
Generator speed (CSD trim)
45
Reactive load sharing control
Voltage regulation
46
Differential protection purpose
Detect short circuits between generator and bus
47
Emergency electrical system requirement
Independent backup power source
48
Typical emergency power duration
At least 30 minutes
49
Common emergency power source
Aircraft battery
50
RAT function
Provide emergency hydraulic/electrical power
51
APU electrical role
Ground and emergency AC power
52
DC emergency bus supplies
Essential flight instruments and systems
53
Manual emergency electrical selection example
EMER ELEC MAN ON
54
Only bus energized when aircraft parked
Hot battery bus
55
Voltage regulation basic principle
Control generator field current
56
Faraday’s law relevance
Voltage depends on flux change rate
57
Obsolete voltage regulation method
Manual rheostat control
58
Triple-unit regulator components
Voltage regulator, current limiter, RCCO
59
Carbon pile regulator feature
Variable resistance via carbon discs
60
Modern voltage regulator type
Solid-state
61
Current limiter purpose
Prevent generator overload
62
Reverse Current Cut-Out purpose
Prevent battery motoring generator
63
Point of regulation location
Near generator output after CTs
64
AC generator sensing device
Current Transformers
65
Two major parts of aircraft electrical systems
Generation subsystem and Distribution subsystem
66
Purpose of generation subsystem
Produces electrical energy (AC or DC)
67
Purpose of distribution subsystem
Delivers electrical energy to aircraft consumers
68
Typical main DC system voltage
28 V DC
69
Starter-generator function
Acts as engine starter then generator in flight
70
Three levels of DC distribution
Main, Essential, Emergency
71
Main DC distribution supplies
Primary consumers
72
Essential DC distribution supplies
Critical systems for safe flight
73
Emergency DC distribution supplies
Critical systems for safe landing
74
Purpose of load shedding
Preserve power for essential systems
75
Definition of busbar
Low-resistance power distribution point
76
Types of DC buses
Main, sub, tie, transfer buses
77
Hot bus definition
Always powered by battery
78
Battery bus definition
Fed through battery relay
79
DC main bus definition
Primary generator-fed bus
80
Essential bus definition
Supplies critical loads
81
Non-essential bus definition
Loads shed during emergencies
82
Standard aircraft AC supply
115 V, 400 Hz, 3-phase
83
IDG function
Provides constant 400 Hz AC
84
VSG characteristic
Variable frequency output
85
AC main buses example
AC-1 and AC-2
86
Purpose of bus tie contactor
Allows cross-feeding between buses
87
AC bus phase composition
Three phase buses A, B, C
88
Manual load shedding examples
GALLEY or UTILITY switches
89
Purpose of power source switching
Connect correct power source automatically
90
Automatic switching controlled by
Generator Control Unit (GCU)
91
Power contactor definition
Electrically controlled heavy-duty switch
92
Reason contactors placed near loads
Reduce wiring weight
93
Modern electrical indication system
Electronic Indicator System (EIS)
94
Magnetic indicator white meaning
Energized
95
Magnetic indicator red meaning
De-energized
96
Magnetic indicator crosshatch meaning
No power
97
Function of main bus
Supplies majority of aircraft loads
98
Function of essential bus
Powers vital flight systems
99
Function of emergency bus
Last-resort battery-powered systems
100
Function of tie/transfer bus
Allows cross-feeding between sources
101
Battery endurance for essential loads
~30 minutes (aircraft dependent)
102
Purpose of inverter
Convert DC to AC
103
Typical inverter outputs
26 Vac or 115 Vac, 400 Hz
104
Two types of inverters
Rotary and Static
105
Advantage of static inverter
High efficiency, low maintenance
106
Purpose of transformer
Change AC voltage level
107
Transformer limitation
AC only; cannot convert AC/DC
108
Purpose of rectifier
Convert AC to DC
109
Half-wave rectifier feature
Uses one half of AC cycle
110
Full-wave rectifier feature
Uses both halves of AC cycle
111
Purpose of TRU
Convert AC to DC in one unit
112
Typical TRU output
28 Vdc
113
TRU efficiency range
85–92%
114
TRU power factor
Greater than 0.96
115
Single-phase TRU diode count
4 diodes
116
Three-phase TRU diode count
6 diodes
117
Advantage of three-phase TRU
Smoother DC output
118
Main DC sources on AC aircraft
TRUs
119
Reason electrical protection required
Prevent fire and equipment damage
120
Definition of short circuit
Low-resistance unintended current path
121
Definition of overload
Current exceeds circuit rating
122
Primary circuit protection devices
Fuses and circuit breakers
123
Fuse characteristic
Melts and must be replaced
124
Why CBs preferred over fuses
Can be reset
125
Circuit breaker function
Interrupts excessive current
126
CB installation principle
Installed close to wiring
127
Policy on CB reset in flight
Maximum one reset attempt
128
Push-pull CB characteristic
Thermal pop-out design
129
Thermal CB operating principle
Bimetal strip heats and trips
130
Magnetic CB operating principle
Electromagnet trips breaker
131
Virtual circuit breaker definition
Computer-monitored electronic protection
132
RCCB definition
Remote Control Circuit Breaker
133
Purpose of RCCBs
Reduce wiring weight and panel space
134
SSPC definition
Solid State Power Controller
135
Aircraft using SSPCs
A380
136
Purpose of ground power
Support ground operations and engine start
137
Why batteries not used for full ground ops
Limited capacity
138
DC ground power voltage
28 V DC
139
AC ground power standard
115/200 Vac, 3-phase, 400 Hz
140
Modern DC ground connector pins
2 positive, 1 negative
141
Purpose of short positive pin
Operate external power relay
142
Function of power selector switch EXT
Connect GPU to main DC bus
143
Battery isolation during DC GPU use
Battery not charged directly
144
AC ground connector pin count
6 pins
145
AC ground connector control pins purpose
Prevent arcing on disconnect
146
AC ground power feeds
Main AC bus
147
TRU role during AC ground power
Provide DC power
148
Ground power connector inspection focus
Damage, bent pins, corrosion
149
GO/NO-GO test purpose
Check pin wear
150
GO/NO-GO reject condition
Gauge fits over pin
