AGK Electrics Flashcards
Ohms law
V = IR
Power Equation
P = IV
P = IE
(E=EMF)
Lorentz law
F = BLI
Force= Field x Length x Current
CS25
CS23
Larger aircraft specifications
Smaller aircraft specifications
Emergency electrical configuration can power aircraft for how long ?
2 hours
Minimum battery power time for any aircraft ?
30 minutes
What electrical system is on A320 or B737
115/200 volt, 3 phase AC @ [400Hz]
Frequency on an A320 or B737
400 HZ constant
Capacitor impact on DC flow ?
Capacitors block DC Flow
Capacitance units ?
Farrads (F)
Resistors in series ?
Add up RT= R1+R2
Resistors in parallel ?
Add up in proportion 1/RT= 1/R1 + 1/R2
(Whether they want answer proportional to or not will vary with question)
Circuit flow direction in batteries ?
Conventional flow
(Positive to negative. Physically correct is negative to positive)
Shorter circuit means ?
Decreased resistance so therefore current increases
Circuit breaker and fuse role ?
To protect against over-currents
How are static discharge wicks attached to the aircraft ?
They are bolted to the wingtips
Max number you can lose is three
Why must aircraft components be electrically bonded ?
to prevent radio interference, Crackle or Hiss
Ensure a low resistance path to the static wicks
What is grounding ?
Removing charge from the airframe by connecting it into the ground to discharge, must be connected before re-fuelling commences
Cell structure ?
Two dis-similar metals and an electrolyte
Lead Acid battery voltages ?
Comprised of 6 cells.
Cell voltage = 2.2V offload
Terminal voltage = 12-12.6V (very small resistance means it isn’t exactly 2.2 x 6)
Nominal voltage = 12V
Modern batteries are ?
Nickel cadmium (Nicad)
Lithium Polymer (LiPo)
Lithium Ion (LiOn)
Modern battery voltages ?
comprised of 10 cells (jpn +1 spare)
Cell voltage = 1.3V on/offload
Terminal voltage = 13.2V
Nominal voltage = 12V
Biggest danger of modern batteries is ?
Thermal runaway.
Temperature increases, which causes resistance to decrease, which increases the current, which increases temperature and the cycle of continuously increasing temperature continues until completely submerged in water to cancel out all aspects.
Does thermal runaway only impact damaged batteries ?
No
Battery does not have the be damaged
Electrical pressure other names ?
Voltage
EMF
Potential difference
Batteries use ?
Chemical energy and produce DC
Generators produce ?
AC
(Alternator)
GEARB power sources ?
Power Priority Order
G-Generator
E-External power
A-APU
R-RAT
B-Battery
What are batteries rated in ?
(C-rating)
Amps per Hour (divisible by 100 or 10)
100 AH battery provides 100 Amps for 1 hour
or 1 Amp for 100 hours
Turning things off to reduce battery strain is ?
Load shedding
How to determine battery draw and load ?
Load shedding in conjunction with the Ammeter
Effect on batteries in series ?
The voltage increases - Current capacity of 1 battery
(Voltage is added together, capacity current stays the same)
Effect on batteries in parallel ?
The capacity increases - Voltage of 1 battery
(Capacity current is added together, voltage stays the same)
Battery rating is measured in ?
AH (Amperes per hour)
Effect of batteries in series ?
Voltage is added together
Has the current capacity of 1 battery
Effect of batteries in parallel
Current capacity is added together
Voltage is that of one battery
Rocker switches
Can usually be set in two or three positions
Push button switches
‘Toggle’ between stages, often have backlit text caption to indicate state
Rotary switches
Change resistance
Knob is arrow shaped to indicate selected option
Toggle switch
Can be visually determined if it’s on or off (state). Generally on is up.
Switches in positions where the could be accidentally knocked are often ?
Guarded (require genuine intent to alter)
Red guarded switch means ?
Irreversible action (generator disconnects)
Black guarded switch means ?
It’s a reversible action (Ditching switch)
Circuit breaker is ?
Re-settable
Fuse is ?
Replaceable (10% must be carried on board)
Circuit breaker and fuse function ?
To monitor current, therefore they can also monitor temperature.
How does a fuse work ?
a copper strip in a vacuumed glass tube connected to circuit with a current rating. If that rating is exceeded the copper will melt and disconnect the circuit.
When should you use a fuse of higher rating than required ?
Never
Types of circuit breaker ?
Thermo - temperature
Magnetic - current
Thermomagnetic - both
Efficiency’s of certain circuit breakers ?
Thermo breaker is good for slow current increase.
Magnetic breaker is good for rapid current increases
Thermomagnetic is good for both
Trip free breaker ?
Will not allow contacts to be closed if the fault persists
Non-trip free breaker ?
Can be held closed if the fault persists (Caution)
Labelled trip breakers are known as ?
Tripped and tagged, do not reset
When a magnet is fully magnetised it’s referred to as ?
Saturated, creating a Permanent magnet
A magnet that can be fully magnetised and de-magnetised is known as ?
An electromagnet, and has a controllable Field.
Made from “soft” iron
Electro-magnetic field relationship with current
Field is directly proportional to current .
(Field increase means current increase )
Type of current in an Electro-magnet ?
DC current
Relay role ?
Allows us to switch high voltage high current using low voltage low current
How does a relay work ?
Uses an electromagnetic field generated by a coil wrapped round an iron core to close a switch in a high current circuit
Solenoid process ?
Field is created when a current is applied and pulls inwards, compressing the spring. (Push and pull motion ) (like a punching fist)
Electromagnetic induction is ?
When voltage current is generated in a conductor by it being moved across a magnetic field
If wires are not shielded and a current flows through one, what will happen to close proximity wires ?
A current will begin to flow
What is an Armature
Component where a current is produced when turned in a magnetic field.
Require components for an AC generator, roles.
Rotor = Magnet (rotates)
Stator = Armature (stationary)
DC generator components
Rotor = Armature
Stator = Magnet
Commutator (converts AC into DC by cancelling out bottom half of AC wave)
Frequency formula ?
F = (pole x RPM) / 120
AC waveform shape
Sinusoidal
Most common frequency set up
4 poles, 400Hz = 12’000 RPM
3 phase generator is called ?
+ produce
Polyphase
Creates a much larger and efficient field to directly feed the A/C
What proportional determines generator output and how ?
Field strength,
As Field strength increases, so does current, therefore output is greater.
How is current varied in response to load ?
Voltage regulator, it changes Feild strength in response to load demands
How does a voltage regulator work ?
When an increase of output is required, the variable resistor decreases, so the DC source allows field strength to increased which then increases the output.
Sense role ?
Monitors the output required and communicates with voltage regulator
What does generator control unit control ?
Everything except the voltage regulator
RMS / Vpeak calculation
(RMS is always stated, eg sockets is 240V)
RMS= Vpeak x 0.707
Vpeak= RMS / 0.707
Tolerances for voltage and frequency
Voltage = 115V (+/- 5)
Frequency = 400 (+/- 20)
Voltage splits into -
Line voltage - 200V (used for error checking )
Phase voltage - 115V
P.D across phases
+ to + = 115V ( phase )
+ to - = 200V ( line to line )
What separates the generator from the engine incase of failure ?
Disconnect unit ( dog clutch )
Located between Accessory gearbox and CSDU
Irreversible in flight.
Engine must be off to reconnect
Potential generator failure indicators
High oil temperature and low oil pressure- monitored system.
If occurs Follow checklist !
A well bonded airframe can be used as a common ….. for electrical circuits
Earth return
If a resistor gets hotter ….
(Postive thermal coefficient)
Current reduces as resistance is increased
What is the electrolyte in nickel cadmium batteries ?
Potassium hydroxide
Ac generator (alternator) speed …?
Is constant RPM (CSDU)
Speed determines frequency (400Hz)
What does High oli temp and low oil pressure lead too ?
Drive disconnect, which can’t be disconnected in flight ?
How is generator controlled ?
GCU
GCU functions
Everything apart from voltage regulation
How is a rotating component connected to a non-rotating component in the generator ?
Slip rings and brushes
How is initial excitation achieved in the AC brushless generator ?
A permanent magnet
Inverter converts ?
DC to AC
What does a TRU do ?
Convert AC to DC, usually to a lower voltage
CDSU role ?
Drives the generator at a constant RPM to provide a constant 400 Hz frequency
How is a spinning rotor connected to stationary parts of the generator ?
Slip rings and (carbon) brushes
Issues with DC voltage regulator ?
bruh wear
losses due to friction
How is excitation achieved in an AC brushless generator ?
A permanent magnet
AC Generator paralleling increases ?
available current (same process as batteries)
separated by a paralleling breaker
Rules for when a AC paralleling breaker closes ?
Voltage must be the exact same
frequency must be the exact same
phase must be within 90º
real load must match
DC paralleling rules on breaker closure ?
Voltage must be the exact same (or risk of spark)
Load must match
Rectification is ?
process of converting AC into DC
Very high efficiency
Diodes are used to control current flow
What is a zener diode used for ?
Voltage stabilisation
Purpose of battery cut out is ?
Stop DC alternator becoming a motor
Hot bus is ?
connected directly to the battery and always live
An inverter ?
Produces AC from a DC source
Is a solid state device- Has no moving parts
TRU 2 functions ?
Transform voltage (reduce V 115- 24/29)
rectify current (AC to DC)
(It can only transform AC current)
What TRU is most common on A/C ?
Step down transformer, achieved by swapping sides
What can be said about the power across a TRU ?
Power in the TRU is equal on both sides, no loss or gain.
GCB Is ?
generator control breaker
Makes the circuit online
Breaks the circuit so its offline
Where is GCB ?
Between busbar and generator
ECB is ?
Excitation control breaker (Normally closed)
ECB is closed when engine is off
Controlled by the GCU
Potential fire issues ?
Electrics
Hydraulics
Fuel systems
Bleed air
Major fault is ?
A rising fault
up to 120V
or
up to 420Hz
What happens in event of major fault ?
ECB opens instantaneously and collapses the field, cutting off power immediately, this then shuts off whole AC assembly.
In event of Major fault failure (Abv)
ECB opens
GCB opens
BTB closes
BTB is ?
Bus tie breaker
controlled by corresponding side GCUs
Minor fault ?
A falling fault
down to 110V
or
down to 380Hz
In the event of a minor fault ?
GCB opens
BTB closes
Differential fault is ?
A difference in measured parameters between a generator and bus bar
Motor definition
Converts electrical energy into mechanical energy by generating mechanical rotor drive
Generator definition ?
Converts mechanical energy into electrical energy
Generator and motor relationship ?
Generator creates, motor receives
How is the direction of rotation changed (DC motor) ?
Change/reverse polarity/direction of the applied current
3 methods of connection in a practical DC motor ?
Series wound - (most utilised) - Torque
Parallel/shunt - Speed control (no torque)
Compound wound - Good mix of both
Construction of a diode ?
A P-N junction
Positive type material - (one less electron)
Negative type material - (one extra electron)
Diodes are very sensitive to what ?
Temperature, they will melt if they becomes too hot
How are signal controlled ?
Logic gates ?
AND gates ?
(D shaped with two lines entering flat side and one entering curved side)
TRUTH TABLE
A B Q
0 0 0
1 0 0
0 1 0
1 1 1
OR gates ?
(Crescent shaped with lines going in either peak and out the curve centre)
TRUTH TABLE
A. B. Q.
1. 0. 1
0. 1. 1
1. 1. 1
0. 0. 0
NOT Gate ?
Inversion gate, flips the signal
(Diode shaped but a ball at the end instead of a line, same entry and exit points)
TRUTH TABLE
A. Q
1. 0
0. 1
NAND gate ?
(D shape but has a ball on outside curved surface, two entries on flat side and one through the ball)
TRUTH TABLE
A. B. Q
0. 0. 1
1. 0. 1
0. 1. 1
1. 1. 0
