Aircraft Electrical Systems Flashcards
How many alternators power an aircraft?
-Normally one
-Older aircraft have one generator
What are batteries for in an aircraft?
-For starting and emergencies
-They can be disconnected from the system
-The are not needed in normal flight
How are circuits protected?
-Circuit breakers
-Fuses on really old planes
How are circuits completed?
-Through ground, which is the structure of the aircraft.
-It can be assumed that all ground are connected
Aircraft use what type of electrical systems?
Single wire
What two systems are aircraft circuits divided?
Power and Load
What do power circuits connect to? and where can the power come from?
-Power circuits connect power to the bus.
-Power can come from a battery, generator, alternator, or a GPU.
When an ammeter is wired to each end of a shunt it is not really an ammeter but a?
Micro voltmeter
The shunt is a _____ with known_____. Therefore it will?
-conductor with known resistance.
-Drop a certain amount of voltage as power runs through it
When alternator output is high or low?
-The voltage is at its peak
-The voltages is at its minimum
Even though the ammeter is marked in amps its responding in?
Changes in voltage
What is a zero-center ammeter?
To show at a glance whether the battery is being charged by the alternator or discharging because the alternator output is too low.
When does a normally closed solenoid open?
When it is energized
Why do alternators need to share the load?
One will take over and probably fail while the other one is doing nothing.
How do you avoid excessive flow in a circuit?
By a device that will open the circuit
Where are circuit breakers located any why?
-As near the source as possible
-They are protecting the aircraft wiring
-Individual components may have their own CB’s or fuses
What are Current Limiters?
A type of slow blow fuse that allows a large amount of current to flow for a short length of time but opens if to much current flows for a long period
Hot battery Bus
Has power any time a charged battery is installed
Main battery Bus
Must be connected to the hot battery bus to get power or to ground power. Power for starting comes from this bus
Power for starting comes from which bus?
Main battery bus
Isolation Bus
-Also powered whenever the main battery bus is connected
-Connects the power of the 2 generators
Generator Bus
How generator power gets to dual feed buses
Dual Feed Bus
Divides load into multiple buses so that a fault doesn’t interrupt all power.
Avionics Bus
Can be disconnected from the other power in the aircraft.
What is a GCU?
Generator Control Unit-A line replaceable unit (LRU) that does more or less what you think, controls the generator. It can also control the connection of the generator through bus tie breakers (BTB), which are large circuit breakers that connect busses
What is a BPCU?
A Bus Power Control Unit. Also, an LRU that monitors current throughout the aircraft. If it identifies a fault, it will signal the GCU which might open or close other bus ties
What are current transformers?
Senses the amount of current in any wire using inductance. The BPCU will use it to identify a fault whenever the current amount is out of range
What Bus system was used until the 80’s on multi-engine aircraft?
Parallel bus systems
How did a parallel bus system function?
All power is put on one bus, called the sync bus because the power had to be synchronized for phase and frequency. A third person on the flight deck, the flight engineer, did this.
What is a good thing about a parallel bus?
That when one generator failed nothing had to be done and power simply came from the remaining generators
What is a RAT?
Ram Air Turbine-turns an emergency generator and some also have hydraulic pumps
What bus system is used on current aircraft?
Split Bus System- Reliant on computerized systems in aircraft to control power, and lot of other systems
Do generators need to be synchronized on Split bus systems?
No-no two generators are ever on the same bus
What happens on a split bus system if a generator fails?
The aircraft will have the remaining generator power both buses. When the APU generator comes on-line the airplane will disconnect the remaining generator from one bus and connect the APU to the bus of the failed generator
What is a split parallel system?
Like flying to twin-engine aircraft next to each other.
Do generators need to be synchronized on a split parallel system?
Yes for phase and frequency
What happens if a generator fails on a split parallel system?
One side of the plane could be tied to the other side to keep system functioning.
How is the circuit completed through the generator?
The ground from a load goes to the airframe and the ground from the generator pick up the return current.
What is a single wire system?
A single wire goes from the bus to the load to the ground.
How does a circuit breaker work?
It is made of two dissimilar metals that expand at different rates when heat is passed through them.
What is a split bus relay?
When the avionics bus is separate from the main bus.
NC
Normally Closed
NO
Normally Open
