Electrical Flashcards
What does AVAIL light mean on APU GEN or EXT PWR switches
APU - generator power acceptable
EXT PWR - external power plugged in and power is acceptable
When would a generator DRIVE light illuminate?
- IDG oil pressure low
- IDG oil temperature high
- Generator Control Breaker (GCB) open due to uncorrectable generator frequency fault
Main AC electrical power sources
- 4 Integrated Drive Generators (IDGs) (one mounted to each engines accessory gear box)
- 2 APU generators
- 2 external power sources
What happens if electrical load exceeds power available (airplane or external)?
Electrical Load Control Units (ELCUs) shed AC loads in a programmed sequence until overload is relieved
- Galley busses are shed first, followed by utility busses (galley busses only on passenger)
- Utility Buses 1 and 2 and Galley Buses 1 and 2 (pax) are powered by ELCU logic (Utly Pwr Sw L)
- Utility Buses 3 and 4 and Galley Buses 3 and 4 (pax) are powered by ELCU logic (Utly Pwr Sw R)
When will an IDG be automatically disconnected?
Excessively high IDG oil temperature without prior disconnection by flight crew
When can APU generators be used?
APU auxiliary power can only be used on the ground
Purpose of Split System Breaker (SSB)
- divides the synchronous bus allowing each side of the AC electrical system to be powered by separate auxiliary or external power sources
- Auxiliary and external power sources cannot be connected to the same side of the synchronous bus simultaneously.
What is the meaning of ELEC BUS ISLN on the EICAS display?
The related Bus Tie Breaker (BTB) is open
- can be reset by pushing the Bus Tie Switch Off, and then AUTO, if fault is cleared
- Bus is disconnected from the sync bus
How is AC power distributed?
- four main buses (AC BUS 1, AC BUS 2, AC BUS3, AC BUS 4)
- two transfer buses (CA and FO)
- ground service bus and ground handling bus
- four utility buses
- four galley buses (pax)
- two standby buses (pax)
Purpose of transfer buses and how are they powered?
- provide AC power to critical flight related equipment
- CA transfer bus normally powered by AC Bus 3 (AC Bus 1 as back up)
- FO transfer bus normally powered by AC Bus 2 (AC Bus 1 as back up)
When is the Main Deck Cargo Handling Bus powered?
- powered on the ground when EXT PWR 2 or APU GEN 2 are AVAIL
- pushing the AVAIL source deenergizes the main deck cargo handling bus
- EXT PWR 2 is prioritized over APU GEN 2 if both AVAIL
Components of AC Standby Power System?
- Main standby bus
- APU Standby bus
- Main Battery
- APU Battery (24V)
- Main standby inverter
- APU standby inverter
- Standby Power selector
How long can main battery provide power to the main standby bus with the battery charger unpowered?
30 mins
Power source priority for Main Standby Bus
1) AC Bus 3
2) main standby inverter via main hot battery bus (with batt charger powered via AC 1)
3) mani standby inverter via main hot battery bus (without batt charger powered) - 30 mins
Power source priority of APU standby bus
1) CA transfer bus via AC Bus 3
2) CA transfer bus via AC Bus 1
3) APU standby inverter via APU Hot Batt Bus (charger not powered) - 30 mins
Components of DC electrical System
- 4 Transformer Rectifier Units (TRUs) powered by respective AC bus and providing DC power to respective DC Bus
- 4 DC Isolation Relays (DCIRs) connecting DC Buses to DC Tie Bus
- Main Battery
- APU Battery
Voltage of APU Battery
24V
Main Power Source of APU DC electric starter?
APU start transformer rectifier (TR) via:
Primary:
- utility bus 4 (freight) via external or internal AC source
- galley bus 2 (pax) vis external or internal AC source
Secondary:
- 24V APU Battery (disconnects battery charger during start)
Back up power for IRS
- APU Hot Battery Bus
- Center IRU operates for 5 mins and shutsdown
- ON BATT Light on Maintenance Panel
ELEC DRIVE EICAS Advisory message
- IDG oil pressure low
- IDG oil temp is high
- Generator control open due to uncorrectable freq fault
What does AVAIL light indicate?
- power source is available
- power is acceptable
When is Ground Service Bus Powered
1) AC Bus 1
2) EXT 1 or APU GEN 1 Avail via Ground Service Switch at Door L1
Function of the Standby Power Switch in Auto or Batt
AUTO - allows main and APU standby busses to be powered from available sources
BATT - MX function for testing
- disables man and APU battery chargers
Where is the Electrical Power-Up procedure located?
FCOM VOL 1; Supplemental Procedure 6.1
What happens when you push Generator Drive Disconnect switch
- disconnect IDG from engine
- open related GCB
- can only be reconnected on the ground by MX
Equipment powered by Utility Busses
- FWD Main Fuel Pumps 2 and 3
- FWD Override/Jettison Pumps 2 and 3
- Center Override/Jettison Pump (L)
- Galley Equipment
- APU TR
Describe the electrical load shedding process?
- 4 ELCUs (electrical load control units)
- via logic sheds AC loads by priority until the loads are within the capacity of airplane or ground power generators
- loads are restored when additional AC power becomes available
What is the purpose of the electrical system overload protection?
- provided by load management system
- configured to ensure power is available to critical and essential equipment
Describe the sequence of events during engine start with SSB open (two external sources)
- the IDG powers its side of the synchronous bus when voltage and frequency are acceptable
- The previous power source is disconnected
- When an engine on the opposite side of the airplane is started, the IDG powers its side of the synchronous bus
- The previous power source is disconnected and the SSB closes
What are some of the equipment items powered by the ground service bus?
- main and APU battery chargers
- fuel pumps for APU start
- flight deck flood, navigation, and service lights
- miscellaneous service outlets and equipment
Equipment items powered by the ground handling bus?
- lower cargo handling equipment
- lower cargo compartment lights
- lower cargo doors
- fueling system
- auxiliary hydraulic pump 4
Electrical Configuration during Autoland
- AC and DC buses 1, 2, and 3 are isolated from the sync bus
- provides independent power sources for all 3 power autopilots
- AC 4 powers the sync bus
- BTB 1, 2, and 3 open
- DCIR 1, 2, and 3 open
Equipment powered by Main Standby Bus?
- left EIU, left CDU, left ILS, left VOR
- left ADC, left transponder, left EFIS control panel
- various flight control components
- standby ignition for all engines
- primary EICAS display
- standby instrument lights
- RMI (if installed)
Equipment on the APU standby bus
- left FMC
- left ND
- left PFD
Power Source of Main and APU battery busses
Normal: DC Bus 3 (powered by AC Bus 3 via TR)
Backup: respective Hot Battery Bus
Equipment on Main battery bus
- APU controller (alternate)
- fuel valves (all engines)
- all crossfeed valves
- dome, storm, and selected indicator lights
- IDG disconnect (all engines)
- manual pressurization control
- trailing edge flap control
- CA interphone
- left radio tuning panel
- left VHF
Normal power source of each hot battery bus
- ground service bus via related battery charger (which acts as a TR)
- AC Bus 1 powers ground service bus
Equipment powered by Main Hot Battery Bus
- APU fuel shutoff valve
- spar valves (all engines)
- APU and lower cargo fire extinguishers
- engine fire extinguishers (all engines)
- fire switch unlock (all engines)
Equipment on APU Hot Battery Bus
- IRU left, center, right DC power
- left and right outflow valves
- APU inlet door
- APU controller (primary)
Battery Locatoins
Main Battery - E and E Compartment
APU Battery - Tail
MAIN DECK Handling Bus Priority Power Soure
Priority: EXT PWR 2 (AVAIL)
What EICAS messages may appear during load shedding?
FUEL PRESS CTR L FUEL PUMP 2 FWD FUEL PUMP 3 FWD FUEL OVRD 3 FWD FUEL OVRD 2 FWD
Which busses power AP L, C, and R?
AP L - AC Bus 3
AP C - AC Bus 1
AP R - AC Bus 2
What screens are powered with BATT on and STBY PWR switch Auto?
- Left PFD
- Left ND
- Primary EICAS
- Left CDU
Main Power source of IRUs
3:1:2
Left IRU: AC Bus 3
Center IRU: AC Bus 1
Right IRU: AC Bus 2
