Electrical system Flashcards
Describe the GCU.
Each generator is controlled by a Generator Control Unit (GCU).
The GCU controls the generator frequency and voltage to remain within limits, and controls the Generator Line Contactor (GLC) to close or open as necessary to power the electrical system.
The GCU provides system protection by opening the GLC when the generator power is not within limits.
Describe GEN OFF/R pb.
With the switch ON, the generator field is energized and the GLC will close when the power is normal.
The OFF/R position de-energizes the generator field, opens the GLC, and resets the generator fault circuit.
Each GEN pb has an amber FAULT light that illuminates with an ECAM Caution if the generator is tripped off by the associated GCU.
When a generator is tripped, the associated GLC opens.
How does the drive from the IDG works?
Each engine generator is an integral part of an Integrated Drive Generator (IDG).
The drive portion of the IDG operates similar to an automobile automatic transmission and provides a constant output RPM to drive the generator regardless of the RPM of the powerplant.
Can the IDG be disconnected?
IDG disconnect is accomplished by pressing the momentary IDG pb.
This action disconnects the IDG from the drive shaft and extinguishes the FAULT light.
Note: An IDG disconnect can only be reset on the ground by maintenance.
Describe the GEN pb
A FAULT light in the switch illuminates if the IDG oil temperature is too high or the oil pressure is too low.
The FAULT light is inhibited when N3 is below 52%, so the light is off when the engine is shut down.
The engine must be running for the IDG disconnect to properly function.
If an IDG disconnect is required (normally with the FAULT light on), the E/WD procedure will direct the crew to press the respective IDG switch which will activate a disconnect solenoid.
Do not press the pb more than 3 seconds or the solenoid disconnect mechanism may be damaged.
Describe BTC system.
Each engine generator normally powers the respective AC Bus and then the respective TR.
Each AC Bus (and associated TR) can also be powered by other sources through the Bus Tie system.
The Bus Tie system has a left and right AC BTC and another BTC in the center.
With the BUS TIE switch in the normal AUTO position…
the OFF light in the switch is out and the three BTCs operate automatically to maintain power on both AC Buses if at least one generator is available.
Describe NBPT of AC Buses.
In accordance with the No Break Power Transfer (NBPT) system, transfer of power from one source to another will occur on the ground without a power transient.
The NBPT is automatically performed by synchronizing the generator frequencies and temporarily applying both sources to a bus.
Other than during the limited time of the NBPT, there is no other time that two sources are allowed to power the same AC Bus.
When does an automatic galley shedding may occur?
All three BUS TIE contactors close if only one source of electrical power is available, and in this situation automatic galley shedding may occur if an overload is detected.
What is the priority of AC power delivery?
The priority of AC power delivery with all sources are as follows:
1) Each engine generator has the highest priority to power the respective side.
2) The APU or EXT A has next priority.
a. If both available, the APU has left side priority and EXT A has right side priority.
3) EXT B has next priority.
b. If both EXT are connected, EXT B has left side priority and EXT A has right side priority.
4) If only one generator is available, it has last priority to power the opposite side.
Describe the APU Generator.
The APU generator is directly driven by the APU.
The generator RPM is determined by the APU N speed.
APU Fuel flow is metered to provide the proper N speed to maintain the constant generator frequency.
Describe the functions of EXT A and EXT B switches.
The EXT A switch provides power directly to the right side and the EXT B switch provides power to the left.
The EXT A switch is labeled ON to imply that it can be selected ON or OFF.
The EXT B switch is labeled AUTO to imply that it can be selected to AUTO or OFF.
Since the APU has a higher priority, the AUTO label indicates that EXT B only powers the left side if the APU generator is off.
What does the COMMERCIAL switch controls?
The switch controls power to the galley switch, passenger entertainment systems, cargo loading system, electrical service, water/waste drain mast heat, lavatory and cabin lights, water heater, and in-seat power supply.
Additionally the electrical ice protection for the escape slide lock mechanism(s) is/are powered by this switch.
Describe GALLEY switch in AUTO.
The Galley Power switch is normally in the AUTO position and all galleys are normally powered.
If the ECMU detects an overload or generator failure in flight, the power to one or all galleys will be automatically shed as necessary.
On the ground with APU or External power, the ECMU attempts to supply all galleys.
Describe GALLEY pb FAULT and OFF lights.
An amber FAULT light in the Galley switch illuminates if an overload is detected but the galleys have failed to shed.
Selecting the Galley switch to OFF causes the OFF light to come on and depowers the galleys along with the electrical ice protection for the water/waste drain masts.
