Chapter 6 - Electrical Flashcards
1
Q
Battery Discharge (BAT DISCHARGE) Light
x2
A
- Illuminated (amber) – with BAT switch ON,
- excessive battery discharge detected.
2
Q
TR UNIT Light
2 scenarios
A
Illuminated (amber)
• On the ground
• Any TR has failed.
• In-flight
• TR1 failed; or
• TR2 and TR3 failed.
3
Q
Electrical (ELEC) Light - Illuminated Amber
2x
A
A fault exists in DC power system or standby power system.
Note: Operates only with airplane on ground.
4
Q
Battery (BAT) Switch - OFF
2x conditions
A
Normal power sources available
• Removes power from battery bus and switched hot battery bus
Battery is only power source
• Removes power from battery bus, switched hot battery bus, AC & DC standby
buses, static inverter.
5
Q
Battery (BAT) Switch - ON
2x
A
• Provides power to switched hot battery bus
• Energizes relays to provide automatic switching of standby electrical
system to battery power with loss of normal power
6
Q
CAB/UTIL Switch - OFF
2x
A
Removes electrical power from galley and cabin equipment systems
7
Q
CAB/UTIL Switch - ON
A
supplies electrical power to galley and cabin equipment systems.
(IFE also 115v AC)
8
Q
Generator Drive (DRIVE) Lights
4x
A
Integrated drive generator (IDG) low oil pressure caused by one of the following:
• IDG failure
• Engine shutdown
• IDG automatic disconnect due to high oil temperature
• IDG disconnected through generator drive DISCONNECT switch
9
Q
Generator Drive Disconnect (DISCONNECT) Switches (guarded)
A
Disconnects IDG if electrical power is available and engine start lever is in IDLE.
IDG cannot be reconnected in the air
10
Q
STANDBY Power Off (PWR OFF) Light
A
Illuminated (amber) – one or more of the following busses are unpowered:
• AC standby bus
• DC standby bus
• battery bus.
11
Q
STANDBY POWER Switch (AUTO + AC busses powered)
A
- In flight, or on the ground, and AC transfer busses powered:
- AC standby bus is powered by AC transfer bus 1
- DC standby bus is powered by TR1, TR2 and TR3
12
Q
STANDBY POWER Switch (AUTO + AC busses un-powered)
A
- In flight, or on the ground, loss of all AC power
- AC standby bus is powered by battery through static inverter
- DC standby bus is powered by battery
- Battery bus is powered by battery
13
Q
STANDBY POWER Switch (BAT)
A
- AC standby bus is powered by battery through static inverter
- DC standby bus and battery bus are powered directly by battery
14
Q
STANDBY POWER Switch (OFF)
A
- STANDBY PWR OFF light illuminates
* AC standby bus, static inverter, and DC standby bus are not powered.
15
Q
Ground Power Available (GRD POWER AVAILABLE) Light
A
Illuminated (blue) – ground power is connected and meets airplane power quality
standards
16
Q
Ground Power (GRD PWR) Switch
A
ON – if momentarily moved to ON position and ground power is available:
• removes previously connected power from AC transfer busses
• connects ground power to AC transfer busses if power quality is correct
17
Q
TRANSFER BUS OFF Lights
A
Illuminated (amber) – related transfer bus is not powered.
18
Q
SOURCE OFF Lights
A
Illuminated (amber) – no source has been manually selected to power the related
transfer bus, or the manually selected source has been disconnected
• if a source has been selected to power the opposite transfer bus, both
transfer busses are powered.
19
Q
Generator Off Bus (GEN OFF BUS) Lights
A
Illuminated (blue) – IDG is not supplying power to the related transfer bus.
20
Q
Generator (GEN) Switches (OFF)
A
Disconnects IDG from related AC transfer bus by opening generator circuit
breaker
21
Q
Generator (GEN) Switches (ON)
A
Connects IDG to related AC transfer bus by disconnecting previous power
source and closing generator circuit breaker.
22
Q
BUS TRANSFER Switch (AUTO)
A
BTBs operate automatically to maintain power to AC
transfer busses from any operating generator or external power
• DC cross tie relay automatically provides normal or isolated operation
as required.
23
Q
BUS TRANSFER Switch (OFF)
A
isolates AC transfer bus 1 from AC transfer bus 2 if one IDG is supplying
power to both AC transfer busses
• DC cross tie relay opens to isolate DC bus 1 from DC bus 2.
24
Q
APU Generator Off Bus (GEN OFF BUS) Light
A
Illuminated (blue) – APU is running and not powering a bus.
25
APU Generator (GEN) Switches (OFF)
APU generator powering both AC transfer busses
• moving a single APU GEN switch to OFF illuminates related SOURCE OFF light. APU continues to power AC transfer busses
• subsequently moving other APU GEN switch to OFF disconnects APU generator from tie bus and removes
APU power from AC transfer busses
• APU generator powering one AC transfer bus; IDG powering one AC transfer bus
• moving related APU GEN switch to OFF disconnects APU generator from tie bus and AC transfer bus. IDG powers AC transfer busses.
26
APU Generator (GEN) Switches (ON)
* Neither AC transfer bus powered by IDG – moving a single APU GEN switch to ON:
* connects both AC transfer busses to the APU generator
* disconnects external power, if connected
* opposite SOURCE OFF light illuminates until the other APU GEN switch is moved to ON.
* Both AC transfer busses powered by IDGs – moving an APU GEN switch ON:
* powers the related AC transfer bus from the APU generator
* other AC transfer bus continues to receive power from the IDG.
27
GROUND SERVICE Switch
Provides manual control of ground service busses. Enables servicing airplane using external power without activating AC transfer busses
28
Primary electrical power
Two engine integrated drive generators
| (IDGs) which supply three-phase, 115 volt, 400 cycle alternating current
29
Source of DC Power
Transformer rectifier (TR) units and the main battery/battery charger
30
Backup power for AC & DC standby power
Main & auxiliary batteries
31
There are two basic principles of operation for the 737 electrical system:
* There is no paralleling of the AC sources of power.
| * The source of power being connected to a transfer bus automatically disconnects an existing source
32
The electrical power system may be categorized into three main divisions:
The AC power system, the DC power system, and the standby power system.
33
APU Generator
The APU generator can supply power to both AC transfer busses on the ground or in flight. As the only power source, the APU generator can meet electrical power requirements for all ground conditions and most flight conditions.
34
External Ground Power
When connected, external power can supply power
| to both transfer busses.
35
Ground Service
The switch provides ground power directly to the AC ground service busses for utility outlets, cabin lighting and the battery charger without powering all airplane
electrical busses. The ground service switch is a momentary push button and is overridden when both AC transfer busses are powered.
36
If the BUS TRANS switch is in the AUTO position and the source powering the transfer bus
is disconnected or fails, the source powering the opposite transfer bus automatically picks up
the unpowered transferred bus through the BTBs.
true
37
AC Transfer busses
Whenever external power is powering both transfer busses and the engine generator power is applied to its onside transfer bus, external power continues to supply power to the remaining transfer bus
38
In flight, one engine-driven generator drops offline and the BUS TRANSFER switch is in the AUTO position, what indications will the pilot see on the failed side?
SOURCE OFF and GEN OFF BUS are illuminated and the TRANSFER BUS OFF light remains extinguished.
39
Under which of the following conditions will the Cross Bus Tie Relay automatically open isolating DC bus1 from DC bus 2?
The bus transfer switch is positioned to OFF
40
With the STANDBY POWER switch in the AUTO position, the loss of all normal AC electrical power causes the battery to power the standby loads:
Both in the air and on the ground
41
AC amperage can be observed on the AC ammeter for the source selected by the AC meters
selector.
True
42
Illumination of the amber BAT DISCHARGE light indicates:
Excessive battery discharge is detected with the battery switch on.
43
In flight, an amber TR UNIT light illuminates if
TR 1 or TR2 and TR3 fails.
44
On the ground, an amber ELEC light will illuminate if:
The DC system or standby system equipment has failed.
45
Illumination of the amber Generator Drive (DRIVE) light indicates low oil pressure caused by which of the following?
a. IDG failure.
b. IDG disconnected through generator drive DISCONNECT switch.
c. IDG automatic disconnect due to high oil temperature.
d. All of the answers are correct.
46
Illumination of the blue GRD POWER AVAILABLE light indicates:
External ground power is connected and meets airplane power quality standards
47
The SOURCE OFF light will illuminate when:
a. no source has been manually selected to power the related transfer bus.
b. the manually selected source has been disconnected.
c. both transfer busses are being powered if a source has been selected to power the
opposite transfer bus.
d. All of the answers are correct.
48
Illumination of the GEN OFF BUS light indicates:
a. the related main bus is not powered.
b. the related transfer bus is not powered.
C. the IDG is not supplying power to the related transfer bus.
d. the APU is running and not powering a bus.
49
The APU generator can meet the following conditions:
a. The APU bleed load maximum altitude is 17,000'.
b. The APU bleed and electrical load maximum altitude is 10,000'.
c. The APU electrical load maximum altitude is 41 ,000'.
d. All of the answers are correct
50
Illumination of the amber STANDBY POWER OFF light indicates one or more of the following busses are not powered:
a. the AC standby bus.
b. the DC standby bus.
c. the battery bus.
d. All of the answers are correct
51
Both AC transfer busses can be powered simultaneously by:
a. a single IDG on the ground or in flight.
b. the APU generator while on the ground or in flight.
c. the APU or external power.
d. All answers are correct.
52
When takeoffs are made with the APU powering both transfer busses:
a. one transfer bus will disconnect automatically after lift-off.
b. if the APU is either shut down or fails, the engine generators are automatically
connected to their related transfer busses.
c. the generators will NOT automatically come on line if the APU is either shut down or
fails.
d. both transfer busses will automatically disconnect after lift-off.
53
On the ground, with the BATTERY switch OFF and the STANDBY POWER switch in AUTO, the battery bus is:
Not powered.
54
The GRD PWR switch when momentarily moved to the ON position and ground power is available:
Connects ground power to AC transfer busses if power quality is correct.
55
One basic principle of operation for the 737 electrical system is:
There is no paralleling of the AC sources of power
56
With the BUS TRANSFER switch in AUTO, the cross bus tie relay automatically opens under which of the following conditions?
At glide slope capture during a flight director or autopilot ILS approach.
57
When the STANDBY POWER switch is OFF:
The STANDBY PWR OFF light will be illuminated.
58
The 115 volt AC Standby Bus is powered by
a. the 115 volt AC Transfer Bus No.1 under normal conditions.
b. any source if the AC source powering either transfer bus fails or is disconnected.
c. the battery through the static inverter with a failure of both engine-driven and APU generators.
d. All answers are correct.
59
The cross bus tie relay automatically opens at glide slope capture during a flight director or autopilot ILS approach to:
Prevent a single bus failure from affecting both navigation receivers and flight control
computers.
60
The engine integrated drive generators (IDGs):
Maintains a constant generator speed throughout the normal operating range of the
engine
61
DC busses powered from the battery following a loss of both generators are:
a. switched hot battery bus.
b. battery bus and hot battery bus.
c. DC standby bus.
d. all the answers are correct.
62
With the standby power switch in the AUTO position, automatic switching from normal to alternate power source occurs if:
Either AC transfer bus or the power source for DC bus 1 loses power
63
Which lights are run from the battery bus:
1. Standby Compass
2. Instrument Flood Lights
3. Dome Lights
64
The dome lights in the lavatories is powered by:
Battery bus
65
What is the normal source of AC power?
2 x IDG's - 3 phase, 155v, 400 cycle, alternating current.
66
Which part of the engine drives the IDG?
N2 accessory drive
67
How is the IDG oil cooled?
Engine fan air and fuel flow
67
How is the IDG oil cooled?
Engine fan air and fuel flow
68
How can the IDG be disconnected?
- Automatically - due to high oil temp
| - Manually - by the crew
69
What regulates the constant drive speed to the APU generator?
The fuel control unit by controlling the speed of the APU
70
How is ground power utilised when plugged in?
By pressing the Ground Service lighted button on the FWD flight attendants panel. Two ground service relays connect External Power to the Ground Service Buses.
71
What powers the AC Transfer Buses?
Their respective engine generator via a Generator Breaker
72
What are the three sources of AC power for the Transfer Buses?
1. Engine IDG switches
2. APU generator switches
3. Ground Power switch
73
What does the Bus Tie Breaker (BTB) do?
Automatically power the entire AC electrical system from one AC source
74
On the ground with both engines shutdown or both generator control switches OFF, selecting either APU GEN switch to ON:
Removes Ground Power and powers BOTH Transfer Buses through the BTB.
(SOURCE OFF light stays illuminated on other APU GEN side until switch selected ON).
75
What happens when an APU GEN switch is turned to OFF on the ground with APU power available?
Only the respective SOURCE OFF light illuminates, it does not depower any portion of the system.
76
What happens after starting the first engine and GEN switch is moved to ON?
- Respective generator powers it's transfer bus
- Respective BTB opens
- Respective GEN OFF BUS light extinguishes
- APU continues to power opposite Transfer Bus
77
What happens after starting the second engine and GEN switch is moved to ON?
- Respective generator powers it's transfer bus
- Respective BTB opens
- Respective GEN OFF BUS light extinguishes
- APU GEN OFF light illuminates as it is not powering any systems
78
What happens when a generator fails in-flight?
- Associated transfer bus is powered by other transfer bus through the Bus Tie System
- Associated SOURCE OFF light illuminates
- All electrical systems remain powered
79
Why does the SOURCE OFF light extinguish when the APU is selected after an in-flight generator failure?
Because the Bus Tie System is no longer powering the Transfer Bus.
80
What is the order of load shedding on a single IDG?
1. Galley and main buses on Transfer Bus 2
2. Galley and main buses on Transfer Bus 1
3. IFE buses
81
How can restoration of galley and main bus power be restored?
By cycling CAB/UTIL switch to OFF then ON
82
Load shedding sequence in-flight with the APU as the only power source:
Galley's and main buses followed by the IFE buses. Full load not attempted.
83
Load shedding sequence on the ground with the APU as the only power source:
Galley's and main buses until within limits. Full load attempted.
84
Four requirements for GRD POWER light to illuminate:
1. proper voltage
2. frequency
3. phase rotation
4. free of faults
85
BUS TRANS switch in AUTO:
- Enables BTB's to operate automatically to maintain power on the Transfer Buses from any source
- Enables DC Cross Tie Relay to open automatically when GS is captured
86
BUS TRANS switch in OFF:
- Isolates Transfer Bus 1 from Transfer Bus 2 if only one IDG is available
- Opens the DC Cross Tie Relay
87
When does the SOURCE OFF light illuminate?
- No source has been manually selected to power the related transfer bus, or
- The manually selected source has been disconnected
- The associated Transfer Bus may be powered by the other system, in which case the TRANSFER BUS OFF light will not illuminate
(If a source has been selected to power the opposite transfer bus, both transfer buses are powered)
88
GEN OFF BUS light:
IDG is not supplying power to the related transfer bus.
89
Difference between selecting APU GEN switch to ON when IDG power is available versus Ground Power available:
- Only respective side powered by APU
| - No SOURCE OFF light
90
STANDBY PWR OFF light illuminates for loss of power to:
- AC Standby Bus
- DC Standby Bus
- Battery Bus
91
STANDBY PWR switch in AUTO:
Allows automatic transfer to the Standby Buses on the ground or in-flight
92
The DC Standby Bus is normally powered by:
TR 1 and TR2 with TR3 as a backup source.
93
Loss of AC power in-flight or on the ground with STANDBY POWER switch in AUTO:
- AC STBY Bus is powered by the battery via the Inverter
| - DC STBY Bus also powered by the battery
94
BAT switch OFF:
- Removes power from battery bus and switched hot battery bus when operating with normal power sources available
- Removes power from battery bus, switched hot battery bus, DC standby bus, static inverter, and AC standby bus when battery is only power source.
95
BAT switch ON:
- provides power to switched hot battery bus
- energizes relays to provide automatic switching of standby electrical system to battery power with loss of normal power.
96
The digital display of electrical parameters requires which power source?
Battery bus power
97
A TR UNIT light can indicate either:
- In-flight: failure of TR1 or combined failure of TR2 & 3
| - On the ground: any TR has failed
98
An ELEC light indicates:
A fault exists in DC power system or standby power system. Inhibited in-flight
99
DRIVE light illuminated indicates:
* IDG failure
* engine shutdown
* IDG automatic disconnect due to high oil temperature
* IDG disconnected through generator drive DISCONNECT switch (engines must be operating)
100
IDG Automatic on-line feature:
Engine generators come on-line automatically if takeoff is made with the APU running
101
How is DC power normally provided?
By 28V transformer rectifier units.
102
What is the alternate source of AC Power by the batteries?
Inverter
103
What does TR1 power?
- DC Bus 1
- DC Standby Bus
(can also be powered by TR 2 and 3 if the Cross Tie Relay is closed)
104
What does TR3 power?
Battery bus
105
When does the Cross Tie Relay open?
When GS captured with Autopilot or FD in use or if BUS TRANS switch placed to off.
106
STANDBY PWR OFF light:
One or more of the following busses are unpowered:
• AC standby bus
• DC standby bus
• battery bus.
107
If the BATT switch is off, how is the standby system powered?
By placing the STANDBY BATT switch in the BATT position.
