Electrical Power

Question 1

Electrical system distributes

Answer 1

AC and DC power to the airplane

Question 2

AC power

Answer 2

115 volt at 400hz
2 engine driven IDG (Integrated Drive Generators)
1 APU GEN
1 RAT GEN
1 AC external power input

Question 3

DC power

Answer 3

28 volts
2 Nickel cadmium batteries
1 DC external power input
3 TRU (transformer rectifier units) (convert ac to dc)
1 inverter (converts dc to ac)

Question 4

More systems

Answer 4

4 ICC (Integrated control centers) LICC-RICC-EICC-AICC
2 SPDA (Secondary Power Distribution Assemblies ) Distributes the power to the systems and interfaces with other systems.

Question 5

Circuit breakers

Answer 5

Prevent overload of the system.
When tripped a message appears on EICAS
Can only be reset by maintenance on ground.
Electronic CBs are located inside the SPDA and can be reseted through the MCDU.
Thermal CBs, some located inside the ICCs and cannot be reseted but vital system CBs are stored inside the cockpit (under alphabetical & numerical columns code)

Question 6

IDGs

Answer 6

Are the main AC power sources when the engines are running and are mounted on each main engine gear box.
Generates constant frequency ac power
40kVA, 115v, 400hz 3-phase.
The system is air cooled
Monitored and controlled by the generator control units (GCU)

Question 7

CSD

Answer 7

A Constant speed drive converts variable engine speed into constant generator speed

Question 8

IDG Disconnection

Answer 8

Only authorized maintenance can reset the disconnected IDG once it is disconnected in flight.

Question 9

APU

Answer 9

Is the secondary power source on ground and in abnormal operation in flight. Mounted on the auxiliary power unit.
Provides constant frequency ac power.
40kVA, 115volt, 400Hz, 3-phase
To disconnect it from the bus tie you push in the button in the overhead panel and a white stripe illuminates

Question 10

RAT

Answer 10

Emergency power for the electrical system whenever in flight.
It is installed in the right nose section of the aircraft
It automatically deploys when a sudden loss of ac power in flight occurs.
The kinetic energy is converted into mechanical to drive the generator.
The blades are automatically converted into the airflow.
15kVA, 115VAC, 400Hz, 3-phase
THERE IS NO ALTITUDE RESTRICTION FOR ITS DEPLOYMENT During Flight.

In case there is a failure the message on EICAS will be “BATT DISCHARGING” and in that case can be deployed manually from the cockpit.

Question 11

DC Inverter

Answer 11

Is a static and provides backup ac power when on battery.
Located in the FWD E-bay.
The input is 28volt dc
The output is 115volt ac, 400Hz stabilized, single phase

Question 12

TRUs

Answer 12

The 3 Transformer Rectifier Units are the main dc power whenever the aircraft uses ac buses.
TRU 1 inside the left integrated control center
TRU 2 inside the right integrated control center
TRU 3 inside the emergency integrated control center
Input 115v, 400Hz
Output 28v, 300Amp
We can control them through the overhead panel switches

Question 13

Nickel Cadmium baterries

Answer 13

Are the secondary dc power source.
Battery 2 provides APU start and until RAT starts both batteries provide dc essential loads in case of total power loss.
Battery 1 located in FWD E-bay
Battery 2 located in the AFT E-bay
They are being charged by any available ac source.
They can be controlled by the knobs in the overhead panel from which we can open the conductors and the battery energizes only the HOT BATT Bus

Question 14

ICC

Answer 14

Integrated Control Center
Distributes power
Provides protection from the electrical loads, protects :
LICC :
ac / dc bus 1
ac / dc ground service buses 1
Line replaceable modules (TRU, GCU, External power module)
Several thermal CBs
RICC :
ac/dc bus 2
Dc essential bus 2
Line replacement modules (TRU2,GCU2,AGCU,Several thermal CBs)

EICC :
Ac essential bus / dc essential bus 1&3
Standby ac bus
Hot battery bus 1
Line replacement modules (TRU ESS,Several thermal CBs)

AICC :
APU Start bus
Hot battery bus 2
Several thermal CBs

Question 15

SPDA

Answer 15

Secondary Power Distribution Assembly
2 of them are installed (FWD & MID E-bay) and can be monitored through MCDU in the cockpit.

Is an electrical loads management and power distribution device.
Distributes power from ICC as dictated by logic calculations to several aircraft systems
It has several slots where the modules are connected (like the memory cards in computers). Also there are the electronic CBs and resetting is made through MCDU.
Each module provides Communication - Data processing - Power distribution.

Question 16

Built in tests

Answer 16

Several electrical systems have built-in test capabilities, they detect isolate and locate fauls that occurs.
These systems are :
GCU
AGCU
EPM
SPDA

Levels of testing:
Initiated test
Fault initiated test
Continuous built in test

The results are shown on the EICAS for crew reaction
And send to the CMC (central maintenance computer)

Question 17

IDG Working Logic

Answer 17

IDG 1:
IDG 1 POWERS AC1
AC1 POWERS TRU 1
TRU1 supply’s DC1 and DC ESS 1
Finally supply’s BAT 1

IDG2:
IDG2 powers AC2 and AC ESS
AC2 powers TRU2
TRU 2 supplying DC2 and DC ESS2
Finally supply’s BAT 2

AC ESS:
POWERS TRU ESS AND AC STBY
TRU ESS supplying DC ESS3

Question 18

Electrical system fault logic

Answer 18

1) Onside IDG
2) APU GEN
3) GPU (if on ground)
4) Opposite IDG

1 AC source can supply the entire electrical system
But in full AC power failure, the RAT will automatically deploy to supply all essential buses.

Question 19

What do Tie Buses do?

Answer 19

They achieve connection between the networks. The respective AC BUS will be powered by the other AC BUS through bus tie contactor btc 1 or 2.
Access through the cockpit AC BUS TIES (1 OPEN, AUTO, 2 OPEN)

Question 20

GCU 1&2

Answer 20

GCU 1&2 are LRM (Line replaceable modules) and are located in the Left and Right ICC
They give CONTROL - PROTECTION - DISTRIBUTION of primary AC/DC electrical power.
The distribution is made through signals sent to the GLC 1&2 to close the respective generator

Question 21

External power source options

Answer 21

AC GPU located on the left hand side nose section
DC GPU located on the left hand side aft section

AC for flight preparation and maintenance
DC can ONLY be used for APU start

Question 22

What is the EPM

Answer 22

Is the ground power module located in the left side IDG which controls the operation of the system.
Pushing the GPU button from the cockpit it powers all the AC system.
From the exterior GPU button or from the FWD Galley if button is pushed it operates the ground service buses.

Question 23

The 110volt cockpit plugs

Answer 23

Ac buss 2 a 3 phase converted electricity converted from 115volts to 110volts to supply power in the cockpit plugs.
Can be switched ON/OFF via the PC Outlet control switch. When the green led light illuminates the outlets are available.
In case of a decompression the ac 3phase power will fall and after normal compression is restored the system can be reseted through the PC outlet switch

Question 24

Cabin PC power system

Answer 24

Is powered through AC BUS 1 through a converter ( 115volt —> 110volts) and then to the cabin outlets.
The system will stop when any of the electrical generators will fail.