All normal electrical power shifts automatically except the External Power which must have the EXT PWR pushbutton selected to supply power to the AC bus tie.
Normal priority for AC power is: (work across ELEC panel
from GEN 2)
|
1)
On side engine generator |
PH doesn’t use the On / Off side
terms, below is the official PH version of the Electrical priorities: |
|
2)
External Power |
1)
Engine Generators |
|
3)
APU |
2)
External Power |
|
4)
Off side engine generator |
3)
APU |
|
5)
Emergency Generator (RAT) |
4)
Emergency Generator (RAT) |
|
6)
Batteries |
5)
Batteries |
The only way to power both AC busses from a single power
source is through the AC BUS TIE. The APU and EXT PWR both feed the AC BUS TIE.
Both AC busses connect to the AC BUS TIE as needed. APU will automatically
power AC unless the EXT PWR or ENG GEN is on. If both IDG’s are available then
the AC busses will not be connected to the AC BUS TIE. If only one ENG GEN (no
APU or EXT PWR) is available the opposite AC bus will connect to it through the
AC BUS TIE.
The Electrical system is divided into two main branches.
Both AC and DC are normally separated into two branches with Engine 1 driving
IDG (integrated drive generator) 1 and IDG 1 feeding AC BUS 1. AC BUS 1 then
feeds DC BUS 1 through TR 1 (transformer rectifier). The same happens on side
2.
As long as each engine IDG is available then the two sides
remain electrically isolated. If there is a loss of power on an AC bus then the
remaining powered bus will automatically power the unpowered AC bus through the
AC BUS TIE. If the APU is then started it will automatically power the bus tie
and the failed AC bus. The AC BUS TIE will then be isolated from the normal
powered bus. IDG should not be disconnected when engine not turning (operating
or windmilling) and the IDG disconnect should not be pressed more than 3
seconds. IDG can only be reconnected on the ground.
In case of TR failure the DC busses can be automatically
connected through the DC BAT BUS.
Two batteries are installed. Battery charging is automatic
and is controlled by the BCL (Battery Charge Limiter). The BCL connects the
battery to its respective DC BAT BUS during battery charging and during APU
start. The batteries have an automatic cut-off logic to prevent complete
battery run-down when the aircraft is unpowered and on the ground. This will
shut off the batteries at about 22.5v capacity to ensure APU start after
overnight.
Min Battery voltage is 25.5v. Check battery voltage with the
BAT switch OFF. To charge batteries turn them on by pressing their respective
pb’s and connecting external power. A 20 min. charge is required if BAT voltage
is not enough.
Part of the normal procedures for the Originating Checklist
call for the check of both batteries to make sure that they are charging
properly. Turn off both batteries and then turn them back on. Watch on the ECAM
ELEC page to see that both batteries have initial current charge rates after 10
seconds of less than 60 amps and decreasing (PH 3.4.1).
If all AC (no RAT) is lost a static inverter is connected
from HOT BAT 1 bus to AC ESS bus (not SHED bus). BAT 2 will supply DC ESS (not
SHED) in the event of loss of all AC (no RAT emerg. gen.) regardless. Below 50
kts. AC ESS will no longer be supplied by the inverter and will be unpowered.
DC BAT will connect below 100 kts., it is not supplied above 100 kts. in loss
of all AC.
If both Main AC busses lose power and the airspeed is 100
kts. or more the RAT will automatically deploy. The emergency generator will
then power AC ESS BUS and DC ESS BUS. During the 8 seconds it takes the RAT to
deploy and supply power the batteries will supply the ESS busses (not their
shed busses) and the red FAULT light on the EMER ELEC PWR panel will be on
during those 8 seconds. The RAT emergency generator is lost at landing gear
down (unmodified A320) or less than 125 kts (A319, modified A320, A321) and ND1
and MCDU1 will go out at that time due to loss of AC shed bus. On landing the
DC BAT bus is automatically connected to the batteries when airspeed drops
below 100 kts. When all AC is lost including the RAT emergency generator BAT 1
will supply AC ESS through the static inverter and BAT 2 will supply DC ESS.
When the speed drops below 50 kts. the AC ESS bus is shed and power is lost to
remaining CRT’s (PFD1, ECAM upper). Note: min. RAT speed is 140 kts, RAT
will stall out at less than 125 kts on A319, A321 and modified A320. However,
the RAT will continue to supply hydraulic pressure even after it is unable to
power the emergency generator
AC BUS 1 normally supplies power to AC ESS and DC BUS 1 which eventually feeds DC
ESS. If AC BUS 1 fails the pilot may press the AC ESS FEED pb to ALTN. This
will put the AC ESS BUS on it’s alternate source, GEN 2 through AC BUS 2. AC
Essential Feed will not automatically switch. This is to prevent a bus short on
the AC ESS BUS from then also damaging the GEN 2 bus complex if it has already
caused damage to the GEN 1 bus complex. ECAM will direct whether to actually
repower AC ESS or to leave it unpowered. AC BUS 2 will also supply power to DC
ESS BUS from DC BUS 2 and DC BAT BUS when the AC ESS FEED pb is selected to
ALTN.
If TR1 fails the DC BAT BUS and DC BUS 1 will become
automatically powered by DC BUS 2 which will automatically connect to the DC
BAT BUS.
APU will carry all busses on ground but will not supply main
galley shed busses in-flight. In-flight if only one generator is supplying
entire system then part (321: all galley power) of the galley load and
passenger in-seat power supply is shed.
GEN 1 Line (7.1.9) –
If there is smoke in the avionics compartment the amber SMOKE light will come
on in the GEN 1 LINE pushbutton. The procedure will call for the pilot to press
the pb. This will open the GEN 1 line contactor and depower AC bus 1. GEN 2
will then automatically pick up AC BUS1 through the AC BUS tie. However, GEN 1
will still be powering two wing fuel pumps, one in each wing inner tank. Note: this is not the complete smoke
procedure, just the beginning that deals with the GEN 1 LINE pb.
In loss of all AC (RAT only) emergency the APU is allowed 3
min. for start after EMERG GEN connects. The APU will not start in-flight when
on BAT only (this is due to the DC BAT BUS being disconnected during Electrical
Emergency configuration above 100 kts.). Lights available in loss of all AC
emergency are Capt. instrument lights, F/O dome light (if on DIM or BRT) and
compass/ice light (PH 5.15.1).
If any generator is operating at more than 100% rated load
the GALY & CAB (or GALLEY) pb will illuminate amber FAULT. You will be
directed to select OFF which will then load shed by offloading the main galley,
secondary galley and the in-seat power supply.
Circuit breakers are color coded. Green are monitored by
ECAM. All other colors are not monitored. The ECAM will display C/B TRIPPED ON
OVHD PNL (or REAR PNL) if a green monitored breaker is tripped for more than a
minute. Yellow breakers are pulled during the procedure for flight on battery
power only.
Red capped breakers are NEVER pulled in flight. Red caps are
installed on the wing tip brakes circuit breakers to prevent loss of flap
asymmetry protection. All circuit breakers have a letter (vertical) and number
(horizontal) code.
When on the gate with normal APU
or EXT PWR the GEN 1 & 2 amber FAULT lights will normally be the only amber
FAULT lights on in the overhead panel (with packs ON).
When shutting down the APU and
turning off BATTs allow 2 min. after APU Green AVAIL light goes out to allow
time for APU flap to close (PH 3.16).
Batteries must always be on when
APU is running for fire protection.