Systems - Electrical Flashcards
What is APU’s primary purpose?
Supply electrical. Secondary is pneumatics.
What do you see on APU start?
Door Open
APU in bite
APU gauges
APU SOV open
(DIGS)
What is the function of the APU ECU (engine control unit)?
Generates overspeed signal to cause fuel solenoid SOV to close
Difference in AC and DC electrics
AC - primary
DC - generated off AC
What is function of TRUs?
Converts AC to DC. 4 located in nose.
What does DC Service Switch do?
Connects DC service bus to APU battery direct bus
What are the “hot busses” (always powered by battery)?
APU Battery Bus
Main Battery Bus
DC Emer Bus
What will occur if DC Service Switch is left in the ON position?
Discharge APU battery :(
When will the DC Emer bus appear?
Only if it loses 1 of its 2 sources of power (APU and Batt Bus) or a fault on bus itself
What bus offers fire protection?
DC Emer Bus
What does Battery Master switch connect?
Connects to APU Bat Direct Bus and Main Bat Direct Bus
What are the 2 batteries used for?
(APU battery and Main battery)
Provides DC power for starting APU and in the event of power loss in flight, provides emergency DC power
What are IDGs and where are they located?
Integrated Engine Driven Generator and on accessory gearbox
When do you see IDG disconnect light?
If oil temp is too high or oil pressure is too low - get caution message
(HOTLOP)
What is AC Ess Bus normally powered by?
AC BUS 1
If AC BUS 1 fails, auto switch to BUS 2 (“AC Ess Xfer”)
When will the GCUs trip offline?
Overloaded (KVA too high), over/under voltage, over/under frequency.
If overloaded bus trips gen, it won’t feed same bus to other gens.
Anytime the main tie closes, what is shed?
Utility bus (lightbulbs)
When will ADG deploy?
Loss of power to AC BUS 1 and 2
What do we gain when ADG deploys?
Essential BUS, Hydraulic pump 3B regardless of switch position, slats and flaps operate at 1/2 speed, stab channel 2
Even if ADG auto deploys, why must I pull handle?
ADG handle is the DC handle. It closes the tie so won’t lose DC ESS BUS when WOW or <135 kts
What occurs if ADG fails?
Have ~30 mins on DC power only. Each APU start attempt takes ~6 mins of power.
What 2 parts do the IDGs consist of?
Constant speed drive, and generator
What do the DCPCs do? (DC power centers)
Automatically control DC ties
ADG powers __
Hyd 3 B
AC ESS BUS
Flaps/Slats 1/2 speed
ADG BUS
Stab trim Ch 2
