AGK Electrics Flashcards
How is electric produced onboard and how much do they produce?
Generator (x2) - 90KvA each
External Power - unlimited
APU - 90KvA
Ram Air Turbine (RAT) (Emergency Gen) - 5KvA
Batteries - 1KvA (C Rated)
What is the hierarchy of power?
If one system shuts down, it will go to the next power source
In a downward movement
Gen
Ext
APU
RAM
Batteries
Draw the A320 Schematic
What does TRU stand for ?
Transformer Rectifier Unit (TRU)
What happens if AC1 fails?
AC2 then provides power to the A CESS bus
What is electricity?
Flow of electrons through a conductive material
Atomic Structure
+ Proton
N Neutron
- Electron
What is a chain reaction?
As one electron moves, the one behind it goes into its place, domino effect (think of class mates moving one seat to the right)
The flowing of electrons creates electricity
What causes chain reactions and which provide sufficient power?
Heat - thermocouple
Magnetic Field (moving) - Generator
Chemical Reaction - Battery
Pressure - piezo electric crystals - vibration sensors
Light - solar
Friction - Static electricity
Magnetic field (moving) and chemical reactions provide sufficient power
Direct Current
Electrons flow in a single direction
Good at low range
Low voltage
DC graph
AC graph
Alternating Current
Electrons flow in both directions around the circuit
Travels further as it ignores resistance
What is Voltage and what can it also be called?
Electrical pressure
Potential Difference (P.D.)
Electro-motive Force (EMF)
DC systems
Computers
Screens
Radios
Lights (Navigation)
Good at low range
AC systems
Fuel pumps
Air conditioning packs
Wx Radar
Galleys
Windcreens
~115,000V, 43C = malleable (flex)
~On ground - Single phase
~In flight - Three phase
What is current and how’s it measured?
Flow rate
Amperes (Amps)
I
What is resistance?
Counteracts flow of current
Ohm
Ω
R
Ohms Law equation triangle
V = Volts
I=Current
R= Resistance
What is power and what are there equations?
Electrical work
P(Watts) = V x I
SEP electrical system
12V DC electrical system
MEP electrical system
24V DC electrical system
115v AC from inverter
A320/B737 B757/B767 electrical system
115/200V 3 phase A at 400Hz
+
24V DC system
What is load shredding?
Process of turning off loads you cannot power
~e.g galley
What is frequency?
Rate of change
Positive to negative cycle
F = Hertz (Hz)
1Hz = 1 cycle/sec
What Is A320/B737 frequency and why?
Constant frequency at 400Hz
Why?
More stable power
Smaller generator (can fit onto engine)
Intrinsic relationship between magnetism and electricity
A magnetic field can create electricity
Electricity can create a magnetic field
What is inductance?
Generation of electricity using a magnetic field
What effects voltage?
Speed of movement
Angle at which the conductor cuts the field
Diameter of the conductor
Strength of the field
What is Lorentz Law?
F = B L I
F = Force
B = Field Strength
L = Length of the conductor
I = Resultant Current
What is Capacitance?
The ability of a circuit or component to hold a charge
What is a capacitor also know as and what does it do?
Condenser
Holds charge for a short amount of time
What does a Capacitor measure in?
Farads (F)
What determines capacity (Capacitor)
Distance between plates
Dielectric constant
Surface area of the plates
Capacitor Circuit
Top half = stage 1
Bottom half stage 2
Once capacitor is charged from battery, the switches open and the electricity travels through the bottom half to light the bulb
Then the circuit closes and top half circuit is in used until the capacitor is charged again
To charge the capacitor, you must
Increase frequency
What is a Resistor?
A component designed to provide a predictable resistance
Can be used to control voltage and/or current
Series circuit
Rt = R1 + R2 + R3
If R1 fails then they all fail > not used often in aviation
Parallel Circuit
1 /Rt = 1/R1 + 1/R2 = 1/R3
Answer as a fraction unless specified
What are the three circuit states?
Closed
Open
Short (failure)
Which way is the electron flow in a conventional/non conventional circuit?
Con - +ve to -ve
Non Con - -ve to +ve
What happens in a short circuit?
Resistance decreases but current increases
What does a circuit breaker do?
Protects against over current
Characteristics and materials of conductors
Copper
Gold
Aluminium
Low resistance
Abundance of free electrons (weak bond between electron and nuclei, easy to move)
Characteristic and materials of an insulator (Dielectric)
Air
Paper
Rubber
Glass
Low or no free electrons
What is static electricity?
Air molecules, snow and ice rub against fuselage, depositing electrons
When is static electricity most likely to occur?
Dry conditions with low humidity
What happens if static builds up and how do we prevent this?
Creates a rapid violent discharge back to atmosphere
Prevent by installing STATIC WICKS
What is a static wick?
Constructed of wire or carbon
BOLTED TO FRAME
Wicks deposit the static electricity into the clouds on decent
If a/c experiences a large discharge, some may fall off
A/c deemed grounded if 3 or more are missing
What is a bonding cable?
Joins all parts if the airframe together
Ensures low resistance path to static wicks
Allows a/c to be at the same voltage as static builds up
Prevents radio interference
How do you know if a bonding cable is broken?
Can hear a static “hiss” when using the radio
The hiss comes from the static hitting the airframe and causing a magnetic field
What is a battery and whats its role?
Stores electricity for STBY/EMERGENCY USE
Allows us to start engine or APU
How long does a battery last for when being used in an emergency?
30 mins
Types of battery?
Lead Acid
Nickel Cadmium (Nicd)
Lithium ( Polymer LiPo / Ion LiOn)
What do batteries do? (reaction)
Create a chemical reaction
What current do batteries prodcue?
DC
What are batteries comprised of and what do they do?
Cells
Connected in a series to create an output on terminals
Battery configuration
Lead Acid voltages
Made up of 6 cells
Cell Voltage : 2.2V
Thermal Voltage : 12-12.6V
Nominal Voltage : 12V
Nicd / LiPo / LiOn Voltages
Made of 10 cells + 1 spare (occasionally)
Cell Voltage : 1.3V On/Off Load
Thermal Voltage : 13.2V
Nominal Voltage : 12V
Lead Acid ON/OFF Load Graph
What type of batteries are rechargeable?
Secondary batteries
How must batteries be charged?
At nominal voltage +20%
Takes around 20 mins
How are batteries charged?
The current is reversed through the battery rot create heat
This reveres the chemical change
Resistance decreases
What are the dangers to the modern battery?
Thermal Runaway
Batteries are negative temp coefficient
~As Temp increases, Resistance decreases
