Electrical Flashcards
Standby Power Selector, what are the 3 options and what do they do?
OFF;
standby power not available
main and apu standby busses disconnected from all power sources
AUTO: allows main and apu standby busses to be powered from available sources
BAT:
powers main battery bus from main battery through the main hot battery bus with battery switch ON
powers APU battery bus from APU battery through the APU hot battery bus with battery switch ON
disables main and APU battery chargers
powers main and APU standby busses from their related batteries through their hot battery busses and standby inverters with battery switch ON
BAT position for ground mx only
Battery Switch
ON:
main battery available as backup power source for main battery bus and main standby bus
APU battery available as backup power source for APU battery bus and APU standby bus
OFF: disconnects main and apu batteries from related battery busses
Battery switch off light
amber - battery switch off
Utility Power Switches
On - each switch powers two uktitiy electyrical control units
OFF
-removes power from related ELCUs
-resets fault logic circuitry
Utility Power OFF lights Illuminated (amber)
power removed from related ELCU by fault protection logic or
related utility power switch off
not illuminated during load shedding
APU Generator (APU GEN) Control Switches
push -
AVAIL light illuminated; connects related APU generator to AC electrical system
ON Light illuminated; disconnects related Apu generator from AC electrical system
NOTE; when the main deck cargo handling bus is powered by any generator 2, push it causes main deck cargo handling bus to lose power
APU generator power available (AVAIL) Lights
Illuminated white :
APU generator power quality acceptable
main deck cargo handling bus powered when APU generator 2 avail light illuminated
extinguishes when ON light illuminates
APU Generator Power ON Lights
illuminated white:
related apu generator connected to AC electrical system
extinguishes when avail light illuminates
External Power (EXT PWR) Control Switches
Push:
AVAIL light illuminated connects related external power to AC electrical system
when the main deck cargo handling bus is powered by external power 3 pushing it control switches causes main deck cargo handling bus to lose power
ON light illuminated: disconnects related external power from AC electrical system
BUS TIE Switches
AUTO
arms automatic AC bus tie circuitry
closes related DC isolation relay
OFF
opens BTB and related DCIR
resets fault logic circuitry
generator drive disconnect (DRIVE DISC) switches
Push:
disconnects IDG from engine when above idle speed
opens related generator control breaker (GCB)
Bus isolation (ISLN) Lights
amber-
BTB open
ac bus isolated from synchronous bus
generator DRIVE lights
amber
IDG oil pressure low or
IDG oil temp high or
GCB open due to uncorrectable generator frequency fault
generator control (GEN CONT) Switches
ON - arms GCB to close when generator power quality acceptable
OFF
opens generator field and GCB
resets fault control logic circuitry
isolates generator from its related AC bus
Generator OFF lights
GCB Open
What electrical system is the main source of airplane electrical power?
AC
Where do the main sources of AC power come from?
4 IDGs,2 APU generators, 2 external power sources
What are the main components of an IDG?
AC gen, self contained lube system, auto control and protection components
What causes the IDG to automatically disconnect?
Excessive high drive oil temperature
When an IDG is disconnected can it be restored by the flight crew?
no
how is AC power distributed?
4 main busses, 2 transfer busses, ground service/handling bus
is APU power available in the air?
no
where are the external power receptacles located?
two power receptacles on the lower right forward fuseulage
if only 1 external power source is connected is the SSB open or closed?
Closed. but will open if another external source is connected to the other side.
what happens if power on an AC bus is unacceptable?
The related BTB opens and the bus disconnects from the synchronous bus. The AC bus will remain powered by its IDG. If the IDG cant maintain acceptable power the GCB opens and and BTB closes from the Synchronus
The EICAS message ELEC DRIVE displays for what?
low IDG oil pressure or
high IDG oil temp or
GCB is open due to an uncontrollable generator frequency fault
What causes the IDG to disconnect automatically?
excessive high drive oil temp, this opens the GCB and displays EICAS ELEC GEN OFF
When is AUX power available? where does it come from?
APU, only on the ground
How does an IDG power its related AC Bus?
Through the GCB
How is an AC bus connected to the synchronous bus?
A BTB
What does the EICAS message ELEC BUS ISLN mean?
a BTB is open
What happens if you push the bus tie switch from auto - off - auto?
resets logic circuitry and allows the BTB to close if the fault is corrected
What other busses do the main AC busses power
AC bus 1 powers the ground service bus and provides back up power for both transfer busses.
AC bus 2 powers the first officers transfer bus
AC bus 3 powers the captain transfer bus and main standby bus
each ac bus powers a utlitity bus
The Main AC busses power individual equipment such as?
TRUs, nav radios and flight control computers, flight deck lighting, pitot and window heat
When is the ground service bus powered?
on the ground and in flight whenever AC bus 1 is powered
What does the ground service bus power?
Main and APU battery chargers, fuel pumps for apu start, flight deck flood, nav, service light, misc service outlets and equipment
When is the ground handling bus powered?
on the ground when APU GEN 1 or EXT power 1 is available
What does the ground handling bus power?
Lower cargo handling equipment and compartment lights, fueling system, aux hydraulic pump 4
how many transfer busses are there?
2, CA and FO transfer busses, powers critical flight related equipment
how is the captains transfer bus powered?
Normally AC bus 3, if ac bus 3 is unavailable then AC bus 1
What other bus does the CA transfer bus power?
APU standby bus
What individual equipment does the CA transfer bus power?
Center EfIS/EICAS interface unit (EIU), Left HF, Center ADC (if installed)
How is the first officer transfer bus normally powered
AC Bus 2, if not then AC Bus 1
What individual equipment does FO transfer bus power?
Autothrottle servo, lower eicas display, right ADC / EFIS / EIU/ FMC, Right CDU / HF / ND / PFD
Each Ac bus powers how many utility busses?
1 for 1
How is a utility bus controlled?
ELCU that protects from electrical system from utility bus faults, and provides load management thru auto shedding
What do the utility busses power
Forward main fuel pump 2,3
forward override jettison pump 2,3
center override/jettison pump
galley equipment
Left / right utility switch power which utlitlity busses?
left 1/2 right 3/4
what does the ELEC UTIL BUS EICAS message mean?
one or both utility busses are unpowered due to a fault or the related utility power switch is off
When is the Main deck cargo handling bus powered?
When external power 2 or APU gen 2 is available,
Do you have to select APU or EXT 2 to power the main deck cargo handling bus?
no, as long as they have power it is powered
What happens to the AC and DC busses during an autoland approach
AC and DC busses 1,2,3 are isolated from the synchronous bus to provide independent power sources for the three autopilots. AC bus 4 continues to power the synchronous bus
What happens if an AC or DC bus fails when busses are isolated for Autoland?
the system reconfigures automatically to maintain independent power sources for the three autopilots
What happens to the electrical system during autoland?
AC bus isolation lights 1,2,3 remain extinguished, EICAS message ELEC BUS ISLN not displayed, Message ELECTRICAL SYNOPTIC INHIBITED FOR, and AUTOLAND is displayed
What are the major components of the AC standby system?
main/apu standby busses,
main/apu batteries,
main/apu standby inverters,
standby power selector
When is the electrical system no longer configured for Autoland?
All autopilots disengaged,
TOGA mode is annunciated and the airplane is higher than 100ft,
approach mode is disarmed or deselected,
electrical system is unable to maintain a configuration for Autoland bus isolation
The main standby bus is powered by?
AC bus 3
with the battery switch ON, standby power selector in AUTO, and AC bus 3 not powered, how is the main standby bus powered?
main standby inverter
the main standby inverter (normally unpowered) is activated and receives power from?
Main battery charger through the main hot battery bus
How is the main battery charger normally powered
AC bus 1 through the ground service bus
with the battery switch ON, standby power selector in AUTO, and AC bus 3 and AC bus 1 not powered, how is the main standby bus powered?
main standby inverter through main battery through main hot battery bus, with main battery bus unpowered (normally powered via AC bus 1 through ground service bus), the main battery can provide power to main stand by bus for 30 minutes min
The main standby bus powers what individual equipment
Left EIU / CDU / ILS / VOR,
various flight control components,
standby ignition for all engines
primary EICAS display,
standby instrument lights,
Left ADC / transponder / EFIS control panel
APU standby bus is normally powered by?
Captain transfer bus
with the battery switch ON, standby power selector in AUTO, and the captain transfer bus not powered (loss ac bus 1,3) how is the APU stand by bus powered
APU standby inverter
Where does the APU standby inverter receive power from?
APU battery through the APU hot battery bus, with the apu battery charger unpowered the apu battery can provide power for a minimum of 30 minutes
With the battery switch ON and standby power selector in BAT and main and apu battery chargers disabled, how is each stand by bus powered?
related battery and inverter minimum power of 30 mins
how does the main DC system produce DC power?
4 TRUs
How is each TRU powered?
By its related AC bus
IF a DC Busses respective AC bus or TRU fails, is it still powered?
yes via the DC isolation relays (DCIR) to the DC tie bus
Main DC busses power what individual equipment?
cabin pressure, fuel jettison, and pack temperature controllers
wing anti-ice control
engine driven and hydraulic demand pump control
fuel transfer and jettison valve control
individual nacelle anti ice control
Besides TRU’s what also provides DC power?
battery busses
- main, apu, main hot, apu hot
main and Apu battery bus are normally powered by?
DC bus 3, if either DC bus 3 or ac bus 3 is unpowered then by their respective hot battery bus
the main battery bus provides power to what equipment
APU controller (alternate), fuel valves (all engines), all crossfeed valves,
dome,storm,selected indicator lights
IDG disconnect, manual pressurization control, trailing edge flap control
ISFD (installed)
the apu battery bus powers what equipment
-apu dc fuel pump, engine start air control
-cargo,first officer and service interphones, pa system
-apu and engine fire/overheat detection loops A and B
-APU fire warning horn
how is each hot battery bus normally powered?
ground service bus through its related battery charger.
the main hot battery bus powers what?
apu fuel shutoff valve, spar valves
apu and lower cargo fire extinguishers
engine fire extinguishers (all engines), fire switch unlock (all engines)
the apu hot battery bus powers what?
IRU left, center, right DC power
left and right outflow valves
APU inlet door, APU controller (primary)
