Electrical Flashcards
The electrical system is comprised of
Main AC power
Backup AC power
DC Power
Standby power
Flight control power
ELMS
Electrical Load Management System
- Detects and isolates faults ensuring power is available to critical and essential equipment
- If the electrical loads exceed the power available ELMS automatically sheds AC loads
- When an additional power source is available or the loads decrease, ELMS restores power
What are the normal sources of AC power?
Two engine-driven integrated drive generators
What is the third source of AC power?
- APU generator
- Available for use on the ground or in flight
What is the purpose of the two engine driven backup generators?
Ensure electrical power is available for essential loads during non-normal situations.
What does the main DC electrical system use?
Four transformer rectifier units (TRUs) to produce DC power.
How is standby power made available?
Through either a ram air turbine driven generator or the ship’s battery.
What do the two permanent magnet generators (PMGs) provide a primary source of power to?
The flight controls and are housed within each backup generator
The main AC electrical power sources are:
- Left and right IDGs
- APU generator
- Primary and secondary external power
How many main AC power systems can power the entire plane’s electrical load?
Any two main AC power sources
With both the PRIMARY EXT PWR and SECONDARY EXT PWR selected ON, when the APU generator is available which external power source does it automatically replace?
SECONDARY EXT PWR
What does the Generator Control Unit (GCU) provide?
Automatic control functions and system protection.
When does the DRIVE light illuminate?
When IDG oil pressure is low?
What happens when the DRIVE DISC switch is pushed?
The IDG input is disconnected from the engine and maintenance action on the ground is required to reconnect it.
With the L and R BUS TIE switches in auto, power to the main busses automatically comes from what power sources in priority order?
- Associated engine generator
- APU generator
- Opposite engine generator
In what order does the ELMS shed AC loads?
- Galleys
- L and R utility busses
- Individual equipment powered by the Main AC Busses
How many backup generators can power the frequency converter?
1 at a time
When does the BACKUP GEN power the AC transfer buses
- Only one AC generator is available
- Power to one or both Main AC buses is lost
- APP mode is selected for autoland
- Automatically testing the system after engine start
What are the two sources of power for the ground handling bus?
- Primary external power
- APU generator (when primary external power is not available)
If the APU is running and the primary external power is plugged in, which source of power has priority on the ground handling bus?
Primary external power
What does the Ground Handling Bus power?
- Cargo handling systems
- Fueling/defueling operations
- Other equipment energized only during ground operation
What does the ground service bus power?
- Main and APU battery chargers
- Miscellaneous cabin system loads
What normally powers the ground service bus?
Right main bus
If the right main bus is not powered but the primary external power is plugged in, how is the ground service bus powered
A switch near the 1L door can be used to power the ground service bus
How many batteries does the 777 have?
2 (main battery and APU battery)
What does the main battery power?
- APU control circuits
- APU fuel valves
- APU inlet and exhaust doors
- Standby buses
- Emergency lighting
- LH inboard, outboard, and upper center displays
- LH CDU
How many Transformer Rectifier Units (TRUs) provide DC power?
4
What provides power to the TRUs?
L and R transfer busses
What are the four DC buses the TRUs provide power to?
- L main DC bus
- R main DC bus
- Captain’s flight instrument bus
- FO’s flight instrument bus
The permanent magnet generators are the source of power for what?
The flight controls.
L, R, C power supply assemblies (PSAs) as well as their flight control DC busses
If one or more PMG fail in flight, what powers the flight control DC busses?
The main DC busses, or the captain’s flight instrument bus.
Why does each PSA have a one minute battery?
To ensure uninterrupted power during a transfer of power from one source to another.
What are the critical AC equipment?
- Center ILS
- Center radio altimeter
- Left marker beacon
- Left ATC transponder
- Left VOR
- Engine ignitors
What are the critical DC equipment?
- Captain’s PFD and ND
- FO’s PFD and ND
- Standby instruments
- Left FMC
- Left CDU
- VHF 1 and ACP 1
- Flight interphone
- APU DC fuel pump
- Upper EICAS
What does the standby system consist of?
- Main battery
- Ram air turbine (RAT)
What does the standby system power?
- Battery buses
- Captain and FO flight instrument buses
- AC standby buses
What happens if both transfer buses lose power?
- RAT deploys automatically
- APU starts automatically regardless of switch position
