Electrical Flashcards
Type and number of generators?
4 Variable Frequency Starter/Generators (VFSGs) - 2 on each engine
2 Variable Frequency APU Starter/Generators
Pushing on the BATTERY switch?
Initiates the left Common Commuting Resource start up sequence (2-3 minutes)
Once complete, on-ground battery only mode is energized
Pushing off the BATTERY switch?
De-energizes the on-ground battery only mode, which may take up to two minutes, then the left CCR is de-energized
APU GEN switches to ON?
Arm the associated gen control breaker which closes automatically when power available and closes generator field
APU GEN switches OFF?
Opens the generator control breaker, opens the generator field and resets fault protection systems
EXT PWR switches AVAIL illuminated?
Power is available and of acceptable quality
GEN CTRL switches to ON?
Arms the generator control breaker which allows it to close when power is available and closes the generator field
GEN CTRL OFF lights?
Opens the generator control breaker, opens the generator field and resets the fault protection systems
DRIVE illuminated in Generator Drive Disconnect switch?
Generator drive malfunction has occurred.
Pushing the switch disconnects the drive from the engine
A disconnected drive cannot be re-connected in flight
TOWING POWER switch?
Where is the power derived from?
Requirement to use the switch?
Energizes only those systems required for towing
Power from main and APU batteries
Main battery switch must be OFF
TOWING POWER switch….
Selecting ON, what do you see?
What are the lights to the left?
ON and ON BAT in white
The towing battery charge lights, indicating the level of charge available
White on electrical synoptic?
White at low intensity?
Amber?
Cyan?
White is used for battery indications and no power flow, unless with a green arrow inside, indicating a start in start/gen box
Low intensity white indicates component status is unknown
Amber indicates a problem with the component
Cyan used for labeling
CBIC?
Circuit Breaker Indication and Control
A synoptic that acts as a circuit breaker board
Describe the engine VFSGs
How many volts are they?
Do they have another purpose?
How are they labeled?
Each engine has 2 variable frequency starter generators
Each generator supplies 235 volts
They also operate as electrically-powered starter motors
L1 and L2, R1 and R2
Describe starter/generator function during engine start
Where does the power come from?
Are they singly used as starters, or both?
Power may be supplied by external power, APU power, or the opposite engine’s generated power
Both starters are selected to provide optimal torque
What AC buses do the SGs power?
They power the associated buses,
L1 MAIN, L2 MAIN, R1 MAIN and R2 MAIN
APU starter generators:
How many are there?
What is the output?
2 APU SGs
They each provide 235 volts
Describe SG function during APU start
How is the power for start provided?
How many SGs are used for start?
How is selection made?
Which used for battery start?
Power is supplied by forward external power, the APU battery or engine generated power
Normally a single generator is used for start
The selection of starter is made automatically by the electrical system
The right starter is always used when starting with the APU battery
Is there a switch for ground handling mode?
No. Connecting either forward receptacle powers the ground handling mode. If both sources are connected, the first connected powers this mode
What external power sources are required to start an engine?
What power sources are recommended?
At a minimum, the two forward external power receptacles must be powered.
It is recommended that all three external
power sources are plugged in. Otherwise there is excessive start time and significant load shedding
What will cause the RAT to deploy automatically?
Both engines have failed
All 3 hydraulic system pressures are low
Loss of all power to the Captain’s and FO’s flight instruments
Loss of all 4 hydraulic EMPs and faults occur in the flight control system on approach
Loss of all 4 EMPs and an engine fails on TO or LDG
How many batteries are there?
How are they controlled?
There are two batteries, the main battery and the APU battery.
The main battery is controlled by the battery switch. There is no control of the APU battery; it is fully automatic.
Functions of main battery?
Used for:
Aircraft power-up, Fueling Towing Assists in APU start Electric braking (as backup source) Captain’s flight instruments (until RAT deploys)
How long will the main battery provide standby power?
At least 10 minutes, although normally the RAT will deploy during this period
MAIN BATTERY LOW EICAS
Only seen on ground
MAIN BATTERY DISCH EICAS
Indicates a fault, although battery may still provide power.
Normal message on the ground when battery is the only source of power
APU BATTERY EICAS
Failure of the APU battery
If fails, voltage may drop, APU may shut down,
APU RUNNING will then disappear
Does the APU battery serve a function during towing operations?
Yes…it powers the nav lights
What is the primary source of power for the flight control electronics?
Are they wired in parallel.
Three engine driven Permanent Magnetic Generators (PMGs)
No, they are independent from each other and independent from the main electrical system
Secondary source for flight control power?
28VDC bus and the main battery
There are also dedicated batteries in place to provide backup during temporary power interruptions
How are the EECs powered?
They are each powered by a Permanent Magnetic Alternator (PMA), one on each engine
Backup power for the EECs?
Until the engine spools up, power for EEC is from the 115VAC system, which is also a backup in case a PMA fails
How many Remote Power Distribution Units (RPDUs) are there?
17, located throughout the aircraft to power lower amperage loads
Where is the main battery?
The APU battery?
In the fwd E/E bay.
In the aft E/E bay.
Where are the 235 VAC buses (L1 Main, L2 Main, R1 Main, R2 Main) located?
In the aft E/E bay
How are the 235 VAC buses powered without engine or APU output?
With only forward external power available, the 115 VAC power is converted to 235 VAC
If only APU running, how are the 235 VAC buses powered.
Each APU generator powers two buses
If only one engine running and no APU or external power, how are the 235 VAC buses powered?
The engine generators power their respective buses, and the other two buses are powered by those buses
With APU power available and one engine running, how are the main buses powered?
That engine’s two buses are powered and the APU powers the remaining buses
If one engine generator fails, what happens to its associated bus?
It receives power from another bus
ELEC AC BUS R1
The R1 main bus is inoperative
R1 MAIN on the synoptic will be in amber as well
Where does the electric brake system receive power?
Four power supply units
Each power supply has two separate 28 VDC inputs:
One from the 28 VDC bus system and the other from the main battery (backup)
Where do the large motors get their power?
The large motor loads must be energized by motor controllers, which condition the variable frequency power for that use.
These motor controllers are in the aft E/E bay
Where do the large motor controllers get their power?
From the 235 VAC distribution system, through the Automatic Transformer Rectifier Unit
Some parts are also energized from the aft external power and the APU generators
When external power is the only power source, what motor controllers does the aft external power system energize?
Only the motor controller needed for right engine start
When an APU battery start is required, what motor controller is energized by the APU battery?
Only the motor controller required for an APU battery start
What is the PECS?
Power Electronics Cooling System
When is the PECS system activated?
What is its function?
If one or both engines or the APU is running or if forward external power is connected and selected on
To dissipate the heat created by the high voltage motor controllers
What is a BPCU
How many are there?
What is its purpose?
Bus Power Control Unit
There are two, one functioning and one as a backup
It provides flight deck control and indication, power transfer functions and overall load management and protection
In the TOWING POWER mode, are the radio communication systems powered?
No
What is the on-ground battery only mode and when is it active?
It supports the aircraft power-up sequence
It’s active when the BATTERY switch is ON with the aircraft on the ground with no other power sources
What is the ground handling mode?
When is it active?
Does it have priority over the on-ground battery only mode?
Does it need the BATTERY switch ON?
It is a mode supporting loading, fueling and system power up
It is active when at least one forward external power receptacle is connected (not selected ON)
It does have priority over the on-ground battery only mode
It does not require the BATTERY switch to be ON
When is the GROUND SERVICE mode active?
What does it provide power to?
It is active when the GROUND SERVICE switch on the master attendant switch panel is selected ON while the aircraft is in the ground handling mode
Provides power for
Cabin lighting
Cabin systems
Flight deck dome light
When is the External Power In mode active?
What does one receptacle power?
What do two receptacles power?
It is active when at least one forward power receptacle is connected and selected ON with APU generators OFF
One power source: flight deck equip, cabin lighting and systems, single PEC loop
Two power sources: above, plus NGS, more cabin lighting and systems, hydraulics, IFE and both PEC loops
No packs
When does the in-air RAT only mode occur?
What is another name for it?
It occurs with a loss of all electrical power to the Captain’s and F/O’s flight instruments
Also known as standby power
What is the difference between in-air battery only mode and in-RAT only mode?
In-air battery mode does not power center pitot heat
Which switches are provided for de-energizing non-essential loads if necessary?
IFE/PASS and CABIN/UTILITY switches
What warning exists regarding the APU switch?
Rotate to START, hold momentarily, then allow it to return to ON, smoothly. Do not allow it to snap back to ON
What are the indications that the APU is supplying power?
The OFF lights in the APU GEN switches are extinguished
The APU indications on the status display
APU RUNNING status message on EICAS
What engine speed is required for “cross-start?”
Engine thrust is advanced until N2 is 5% above normal. This ensures optimal electrical performance
How long does APU COOLDOWN last?
2 minutes.
After the ALU COOLDOWN message extinguished, the battery switch may be switched OFF
