Electrical Flashcards
How much energy does the engine alternator provide to the FADEC system
Provides 30 Volts of DC power to the FADEC system.
FADEC Primary Mode system Electrical Order of Priority
1) 30 VDC above 48% N1. (Eng alt)
2) 28 VDC from #1 & #2 DC BUS.
Reversionary Mode Electrical Order of Priority.
1) 30 VDC above 48% N1. (Eng. Alt)
2) 28 VDC from #1 & #2 DC Essential BUS.
3) 24 VDC from ACFT Battery.
Electrical connections of the DECU
P1 (atmospheric pressure in cabin), P3 (compressor discharge pressure), and P2 (computer hook up)
How does a thermistor control unit work?
Thermistor switch operates off DC power. The control unit open and closes relays to provide AC power to the pump.
How does refuel station operate off of battery power only?
As long as battery is plugged in, refuel station operates off the switched battery bus. Refuel station indicator operates off of 115 volts AC which is derived from inverter.
What is a transformer?
It steps down power (for components that operate off of less power).
How can certain components operate off of 26 volts AC?
Because they have a transformer to step down power.
What are the two things the Generator Control unit does?
Voltage regulation and fault monitoring
What kind of faults does the GCU look for?
Over voltage, under voltage, under frequency (gyro example), feeder faults (current transformers check for open or short circuits).
What is the rpm range for an under frequency fault, when gens go offline?
When rrpm drops below 82-85% for 3-7 seconds
When rrpm drops below 82%
How do the generator current transformers work?
They are used to detect feeder faults. Current is induced on wires. The negative current transformer measures what’s coming out of the gen and the positive transformer measures what’s coming in. If no issues, GCU allows power to be connected to system.
Where are components for APU electrical located?
They are located in the right electrical pod even though it powers via the #1 system.
What does a contactor relay do?
Allows for a single power source to be connected to bus
Disconnects inop Gen from bus to prevent reverse current
Completes AC bus tie when required.
There is one for every power source: main gens, apu Gen, ex power.
How many buses does the battery provide for?
3 of the 5 DC buses:
Hot bus
Switched bus
Essential DC (batt switch on)
With the APU Gen on, which buses come on?
All buses minus the hot battery bus.
Why is a SLAB battery safer?
There is not way to overcharge it, thus no battery hot emergency.
How does SLAB battery recharge?
Thru a relay that sends power backwards through the battery which causes chemical reaction that recharges it.
How much power do the transformer rectifiers take and change?
Take 200 AC and transform/rectify into 28 volts DC
What do the reverse current cutout relays do?
They are the managers of the transformer rectifiers:
Prevent reverse current
Connects and disconnects transformer rectifier to/from bbus
Switches on/off rectifier lights
Order of priority in AC system
Main gens
Apu Gen
External power
Order of priority in DC system
External power
transformer rectifiers
Battery
What is on the switched batt bus?
Control centering device release for mag breaks
Ramp and cabin lighting
Forward trans level light
Refuel station (powers inverter)
Emergency exit lights
E-dump
What causes the emergency exit lights to activate?
A hard landing of 3 to 4 g’s as sensed by the inertia switch or a loss of power to the switched bus.
