Electrical Flashcards
It will help if these are done in sequential order but it’s not required. Depends are your understanding of the system.GOOD LUCK!
Click the right arrow to continue…..
Where is the Electrical Power Up Procedure found?
FCOM VOL I - Supplemental Procedures
How many AC PWR sources are available?
8 Total - 4 IDG - 2 APU GEN - 2 EXT PWR
How many busses are powered on a cold airplane? What are they?
The APU and MAIN BATTERY HOT BUSSES
What does AVAIL light mean on EXT PWR switches?
Adequate load and frequency are available.
The APU is INOP and EXT PWR 1 & 2 are selected ON, what busses are powered?
All busses BUT the Main Deck Cargo Handling Bus
How would you power the Main Deck Cargo Handling Bus if both EXT PWR 1 & 2 Switches are ON?
By turning OFF EXT PWR 2 thus making it AVAIL. This will introduce power to the Main Deck Cargo Handling Bus.
With both EXT PWR or APU GENs selected ON, what has occurred to electrical system?
The Split System Breaker (SSB) is opened and each side of the synchronous bus is powered separately by APU or EXT PWR sources.
How does electrical system configure when ENG is started with SSB OPEN?
The IDG will power its respective side of the SYNCHRONOUS BUS what volt and frequency permit. The previous power source will be disconnected.
What is powered by the Main Deck Cargo Handling Bus?
Onboard Main Deck loading equipment and lighting
What items are on the MAIN HOT BATTERY BUS?
- APU/ENG/LL Fire Extinguishers - Fire Switch Unlock - Spar Valves (All ENG) - APU FSOV * so ALL EXTs and FSOV + unlock
What items are on the APU HOT BATTERY BUS?
- APU Controller (Primary) - APU Inlet Door - IRU DC PWR - Outflow Valves
So we have the APU and MAIN BATTERY HOT BUS equipment available and now we turn the BATTERY switch to ON. What have we done?
Powered the MAIN BATTERY and APU BATTERY BUSSES
What items are on the MAIN BATTERY BUS?
- APU Controller (Secondary) - ENG Fuel Valves - ENG XFEED Valves ==================== Dome, Storm, Selector Lights IDG Disconnect Manual Pressurization Control Trailing Edge Flap Control CA Interphone, Left Radio Tuning, L VHF
How is the MAIN BATTERY BUS powered? Normal and Backup?
Normally DC BUS 3. If not available, powered by the MAIN HOT BATTERY BUS
What items are on the APU BATTERY BUS?
- APU Fire Detection + Horn - APU DC Fuel Pump - Interphones
How is the APU BATTERY BUS powered? Normal and Backup?
Same as MAIN BATTERY BUS, via DC BUS 3. If not available, powered by APU HOT BATTERY BUS
How many total busses are powered with the BATTERY ON and STANDBY Switch in AUTO (assuming no AC PWR is available)?
6 busses total. HOT, MAIN, and STANDBY BUSSES (via inverters)
Once AC PWR is available, how is MAIN HOT BATTERY BUS powered?
Via AC BUS 1 –> GROUND SERVICE BUS –> MAIN BATT CHARGER
Once AC PWR is available how is the APU HOT BATTERY BUS powered?
Same as MAIN HOT BATT BUS via AC BUS 1 –> GROUND SERVICE BUS –> APU BATT CHARGER
Once AC PWR is available, how are STANDBY BUSSES powered?
AC BUS 3 –> MAIN STANDBY BUS AC BUS 3 –> CA’s XFER BUS –> APU STANDBY BUS
Name some equipment on the MAIN STANDBY BUS?
- Primary EICAS - Left EIU, CDU, EFIS - Left ADC, ILS, VOR, RMI - Standby IGN
What equipment is on the APU STANDBY BUS?
LEFT FMC, ND, and PFD
Do we use the BAT position of STANDBY PWR selector?
NO, for MX use only.
What is disabled when the STANDBY PWR selector is in the BAT position?
The battery chargers.
How long will battery power energize the STANDBY BUSSES?
At least 30 minutes.
How many IDG are available from the aircraft engines? What type of power is provided?
4 engine driven IDGs provide AC power to the electrical system via Generator Control Breakers (GCBs)
With GEN CONT switch ON, when will the respective GCB close?
When the IDG voltage and frequency are within acceptable limits?
How do we manually OPEN the GCB and what will the switch indication be?
By pushing the respective GEN CONT switch. The ON light will go out and the bottom OFF light will illuminate.
What occurs when you turn the GEN CONT switch to OFF?
- Isolate IDG from AC BUS by opening GCB - Resets fault logic
What does both an ON and OFF light on a GEN CONT switch mean?
A fault has occurred and the GCB has automatically opened.
What does pushing the DRIVE DISC switch do to respective IDG?
Disconnects IDG from its respective engine.
DRIVE will appear on the DRIVE DISC switch when its pushed as referenced above. What other time will it illume?
- IDG HI OIL TEMP - IDG LO OIL PRESS - FAULT (Uncorrectable)
If the DRIVE DISC is pressed to manually disconnect an IDG, what other indication is displayed on the electrical panel?
OFF will be illuminated on the respective GEN CONT switch.
Once disconnected from its engine, how and when can it be reconnected?
Only on the ground by MX personnel.
How are the main AC BUSSES connected to the SYNCRONOUS BUS?
Via the respective Bus Tie Breaker.
What happens when we push the BTB switch and select OFF?
- Opens BTB - Opens related DCIR
If AUTO and ISLN both appear in the Bus Tie Switch, what has occurred?
A fault has occurred and system logic has opened the breaker to isolate the AC BUS from the SYNC BUS
What is the purpose of the SYNCHRONOUS BUS?
Connects the 4 AC BUSSES and allows the IDGs to operated in parallel.
How many UTILITY BUSSES are there and how are they powered?
We have 4 UTILITY BUSSES, each powered by an AC BUS
What do the UTILITY BUS switches control?
The L UTILITY BUS switch controls UTILITY BUSSES 1 & 2. The R UTILITY BUS switch controls UTILITY BUSSES 3 & 4. Pushing the button will provide power from the respective AC BUS to the UTILITY BUS via the ECLU.
What do the UTILITY BUSSES power?
- FWD Main Fuel Pumps 2 & 3 - FWD O/J Fuel Pumps 2 & 3 - Center Wing Tank O/J Pumps - Galley Equipment - TR for APU Start
Speaking of UTILITY BUSSES, what happens if electrical load exceeds power available?
The ECLU will shed AC loads by priority until loads are with limits. EICAS messages may appear; ie (FUEL PUMP 3 FWD). They are restored in reverse order.
What is the primary purpose of the ECLUs that control the UTILITY BUSSES?
Control load shedding should demand exceed supply.
Moving along, lets talk TRANSFER BUSSES. What indications are there for them?
There are no flight deck controls or indication for the TRANSFER BUSSES.
How many TRANSFER BUSSES are there?
Two. The CA and FO TRANSFER BUSSES
What equipment is powered by the TRANSFER BUSSES?
CAPTAIN ========= Center EFIS/EICAS EIU Center ADC Left HF FIRST OFFICER ============== Lower EICAS Autothrottle Servo Right ADC, EFIS, EIU, FMC Right CDU, HF, ND, PFD
How are the TRANSFER BUSSES powered? Primary and Backup.
AC BUS 3 –> CA TRANSFER BUS AC BUS 2 –> FO TRANSFER BUS They are both backed up by AC BUS 1.
What equipment is powered by the GROUND HANDLING BUS?
F - Fuel Systems A - AUX HYD 4 L - Lights (Flt Deck) L - Lower Cargo Equip/Lights
When is the GROUND HANDLING BUS powered?
Only on the ground when the EXT PWR 1 or APU GEN 1 is AVAIL/ON. If both are AVAIL, EXT PWR 1 is used.
What equipment is on the GROUND SERVICE BUS?
C - Chargers (Main & APU) L - Lights (NAV, SVC, Flood) A - APU Fuel Pumps (start) M - Misc Outlets & Equip
When is the GROUND SERVICE BUS powered?
On the ground or in flight when AC BUS 1 is powered.
How can the GROUND SERVICE BUS be powered on the ground when AC BUS 1 is not powered?
By pushing the Ground Service Switch on the cabin panel at door L1.
So we push the Ground Service Switch to power the bus. What is providing power if AC BUS 1 is not available?
Whatever is providing power to the Ground Handling Bus. Either EXT PWR 1 AVAIL or APU GEN 1 AVAIL.
When is the MAIN DECK HANDLING BUS powered?
When EXT PWR 2 or APU GEN 2 is AVAIL. If both are AVAIL, EXT PWR 2 is used.
Why does EXT PWR 2 or APU GEN 2 have to be AVAIL to power the MAIN DECK HANDLING BUS?
Because neither power source can power both the airplane electrical busses and MAIN DECK HANDLING BUS at the same time. Demand exceeds supply.
With regards to the MAIN DECK HANDLING BUS, what happens if both EXT PWR 2 and APU GEN 2 are AVAIL and EXT PWR 2 is turned ON?
The MAIN DECK HANDLING BUS will automatically be powered by APU GEN 2.
How is DC PWR produced on the airplane?
Each AC BUS powers a Transformer Rectifier (TR) which provides DC PWR to a DC BUS
How are the DC BUSSES interconnected?
Via their respective DCIR and the DC TIE BUS.
Can an ILS approach be flown will loss of all normal AC power?
Yes, but no FD or A/P
Is trim available with loss of all normal AC power?
Only with the alternate trim switches on the aisle stand.
