Electrical System Flashcards
IDG 1 and IDG 2 Selector Knob
-AUTO
This position allows the IDG contactor to close, connecting the IDG to the respective AC BUS automatically, according to system logic
IDG 1 and IDG 2 Selector Knob
-OFF
Opens the IDG contactor isolating the IDG from the respective AC BUS
IDG 1 and IDG 2 Selector Knob
-DISC
Must be held in this position for one second to mechanically disconnect the IDG
Can’t be reconnected in flight
Normal AC Bus Priority
Onside IDG
AC BUS Tie
Offside IDG
Illumination of the Amber LED next to IDG DISC
Indicates to which pilot which IDG to disconnect
Will illuminate in association with the IDG 1(2) caution EICAS message & will extinguish when IDG is disconnected.
HOTLOP
-High oil temperature or Low oil pressure
AC BUS TIES Selector Knob
-1 OPEN
Opens the Bus Tie Contactor (BTC) 1, segregating AC BUS 1 from the AC BUS Tie
AC BUS TIES Selector Knob
-AUTO
This position allows automatic operation of the BTC’s according to system logic
AC BUS TIES Selector Knob
-2 OPEN
Opens the Bus Tie Contactor (BTC) 2, segregating AC BUS 2 from the AC BUS TIE
AC BUS Tie Priority
APU
GPU
IDG
GPU Button
-PUSH IN
Connects the AC GPU to the AC BUS Tie, according to the source priority
GPU Button
-PUSH OUT
Isolates the AC GPU from the AC BUS Tie
GPU Button
-AVAIL Light
AVIL will illuminate with the button pushed in or out when the AC GPU is connected, but is not powering the AC BUS Tie. Also indicates GPU is set to correct power setting.
GPU Button
-IN USE Light
Will only illuminate when button is pushed in & the AC GPU is powering the AC BUS Tie
APU GEN Button
-PUSH IN
This position allows the APU generator to connect to the AC BUS Tie, automatically according to source priority
APU GEN Button
-Push OUT
Opens the APU generator contactor and isolates the APU generator from the AC BUS Tie. The APU is tripped off line and de-excited
TRU ESS Toggle Switch
-AUTO
This position allows automatic connection of the TRU ESS to the DC ESS BUS 3
TRU ESS Toggle Switch
-OFF
Isolates the TRU ESS from DC ESS BUS 3
TRU 1 and TRU 2 Toggle Switches
-AUTO
This position allows automatic connection of the TRU 1(2) to the respective DC BUS 1(2)
TRU 1 and TRU 2 Toggle Switch
-OFF
Isolates the TRU 1(2) from the respective DC BUS 1(2)
BATT 1 Selector Knob
-ON
The battery is connected to the DC ESS BUS 1
BATT 1 Selector Knob
-OFF
The battery supplies power to HOT BATT BUS 1 only
DC BUS TIES Toggle Switch
-AUTO
This position allows automatic operation of the DC Tie contactor’s (1 DCTC / 1 & 2 ETC’s) according to system logic
DC BUS TIES Toggle Switch
-OFF
Opens all DC Tie contactors
BATT 2 Selector Knob
-AUTO
This position connects BATT2 to either the DC ESS BUS 2 or the APU START BUS automatically, according to system logic
BATT 2 Selector Knob
-OFF
The battery supplies power to HOT BATT BUS 2 only
AC Power
2 IDG's (115 VAC, 400 Hz, 40 KVA) 1 APU (115 VAC, 400 Hz, 40 KVA) 1 AC GPU (115 VAC, 400 Hz, 40 KVA) 1 RAT (115 VAC, 400 Hz, 15 KVA) 1 Inverter (250 V)
1 IDG can power both AC Buses
On ground & In-flight
APU can power both AC Buses
On ground & In-flight up to FL330
GPU can power both AC Buses
On ground only
Primary source of AC power
IDG
IDG Selector Knob
AUTO- System logic controls contactor
OFF- Opens contactor
DISC- Mechanically disconnects the CSD from IDG
Can the flight crew reconnect an IDG
No, maintenance function only
Amber Light accompanied by an EICAS oil message indicates?
IDG disconnect is required
ICC
Integrated Control Center (4)
-Line replaceable
SPDA
Secondary power distribution assembly (2)
- An electric load management unit
- Receives power from ICC’s
- Distributes power according to system logic
CSD
Constant speed drive
Converts variable engine speed into constant generator speed
IDG oil system is cooled how?
Air cooled
GCU
Generator control unit
Illumination of the amber LED next to IDG DISC indicates?
HOTLOP
-High oil temperature or low oil pressure
APU
Auxiliary Power Unit
-Secondary source of AC Power
Required for APU Start?
BATT 1 & 2 or BATT 1 & DC GPU
Which BATT is used to control APU’s FADEC?
BATT 1
Why is BATT 2 isolated from the network during APU start?
To exclusively power the APU START BUS
Minimum VDC for APU Start?
22.5 VDC
Minimum VDC required to close batter contactor?
18.0 VDC
Minimum BATT 2 temperature for start?
-20 C
AC GPU
AC Ground Power Unit
-Secondary AC power source
GPU power can be turned on in 3 locations
- Cockpit Overhead Panel
- AC GPU Panel (only powers ground service bus)
- Opposite FWD Lav (only powers ground service bus)
Normal AC Electrical Priority
On-side IDG
APU
GPU
Cross-side IDG
Inverter
- Powers the AC STANDBY BUS when normal AC power source is not available
- Allows “A” igniters to always have power source
RAT
- Ram Air Turbine
- Emergency AC Power source
- No restriction for deployment
- Manual deployment available
RAT supplies power to which BUS
AC ESS BUS
Minimum airspeed for RAT
130 knots
-As airspeed decreases, load shedding occurs until AC ESS BUS is not longer powered
DC power provided by?
Transformer Rectifier Unit (TRU)
-28 VDC, 300 A
2 Batteries
-24 VDC, 27 AH
1 DC GPU
-28 VDC
Primary source of DC power?
TRU’s
Function of TRU
Convert 115 VAC to 28 VDC
RAGO
AC System Priority
R- Respective IDG
A- APU
G- GPU
O- Opposite IDG
Electrical Emergency Situation
-Batteries Only
- Screen 2 (PFD)
- Screen 3 (EICAS)
- IESS
- Clock
- FO MCDU
- CA CCD
- 2 Comm panels
- CA Display panel
- CA Reversionary panel
- Light for magnetic compass
DC HOT BATT BUS 1
- Engine 1A Fire Extinguisher
- Engine 2A Fire Extinguisher
- Engine Fuel SOV 1
- Hydraulic system SOV 1
- Engine 1 oil level indication
- Courtesy / Service lights
- DC ceiling lights
DC HOT BATT BUS 2
- Engine 1B Fire Extinguisher
- Engine 2 B Fire Extinguisher
- Engine Fuel SOV 2
- Hydraulic system SOV 2
- Engine 2 oil level indication
- CMC
- Panel refuel
- Water and waste system
EPC BATT 1(2) Over temp
Associated Battery…………………………OFF
Note– Do not start the APU
Batteries
(2) NiCad Batteries
- Secondary source of DC power
- Back-up for DC ESS BUS
- Charged via any AC power source through TRU’s
- 18.0 volt min to close battery contactor
- Will provide 10 minutes of power during an electrical emergency
DC GPU
- Can replace BATT 2 during APU start
- Can only be turned on by a ground ramp button
Function of ICC’s and SPDA’s
ICC’s collect and confirm the power is safe and then sends it to the SPDA’s, which distributes it
How many networks make up the electrical system on the airplane? Why?
2 independent networks for redundancy and fault isolation
What happens if a power generating source fails?
Bus ties automatically connect to provide no system degradation
What components power the AC system?
1 IDG's APU Inverter RAT AC GPU
What components power the DC system?
2 NiCad batteries
2 TRU’s
DC GPU
How does the IDG maintain a stable power output?
A constant speed drive (CSD) attaches the IDG to the AGB (accessory gear box)
What monitors and controls the IDG’s?
Each has a generator control unit
Can one IDG power the entire electrical system?
Yes
What will cause the amber IDG light on the overhead panel to illuminate?
High oil temp
Low oil pressure
HOTLOP
If an IDG is manually disconnected can it be reconnected in flight?
No
What is the primary purpose of the AC generators?
To power the AC BUSSES and AC ESS BUS which power the 3 TRU’s (1, 2 & ESS)
What is the purpose of the TRU’s?
To convert 115 VAC to 28 VDC
Can an APU replace a failed IDG?
Yes
What is the AC electrical system’s priority?
Onside (IDG)
Inside (APU)
Outside (GPU)
Cross-side (Other IDG)
How is it known that an AC GPU is hooked up to the airplane and ready to provide electricity?
GPU button displays AVAIL and the GPU icon is presented on the electrical synoptic page
-Once the GPU button is pushed in, the button will display IN USE provided another AC power source is not available
What does it mean if the AC GPU is plugged in and the outside GPU panel button displays IN USE?
- Ground service bus is in use
- Cockpit GPU button will display AVAIL even though the ground service bus is in use
If the airplane is using the AC GPU and the APU is started what should the pilot be sure to do?
Deselect the GPU button before the next GPU connection
What will charge the batteries?
Any AC power source
How long will the aircraft’s batteries last with no recharging?
10 minutes
What is the purpose of the DC GPU receptacle?
For APU start when batteries
What is the minimum battery temp for APU start?
-20 C
What is the minimum voltage to close the battery bus ties?
18 volts
What battery is used for the APU start?
BATT 2 powers the APU Start Bus
BATT 1 powers the FADEC & EICAS for monitoring
What is the purpose of the inverter?
Converts 28 VDC from the batteries to 115 VAC to power the AC STANDBY BUS when an AC source is not available
What is on the AC STANDBY BUS?
Engine exciters 1A & 2A
What powers the RAT?
Airflow turns the RAT propeller which spins the turbine inside
When will the RAT deploy?
Automatically deploys if AC BUSSES are not powered or manually by pilot
How long after deployment before the RAT will supply power?
8 seconds
Is there a total loss of power during the 8 second RAT deployment?
No. Batteries supply power to the DC ESS BUSSES and AC STANDBY BUS
What does the RAT power?
ESS BUSSES
What is the minimum airspeed for the RAT?
130, load shedding occurs below this speed
When is the RAT icon is displayed on the electrical synoptic page?
When the RAT is deployed
What manages the electrical system?
4 Integrated Control Center’s (ICC) &
2 Secondary Power Distribution Assemblies (SPDA)
What is an ICC?
An electrical control device which provides power distribution and protection for electrical loads
What is an SPDA?
An electrical load-management unit (powered by the ICC’s) that distributes electrical loads to aircraft systems according to distribution logic
Can the flight crew reset the ICC and SPDA remote electronic CB’s
- ICC CB’s can only be reset by maintenance
- SPDA CB’s can be reset via the MCDU
