AES Flashcards
Difference between primary and secondary batteries?
Primary - Unable to be recharges / needs to be replaced
Secondary - Rechargeable
Primary and secondary purpose of an aircraft battery?
Primary purpose - Emergency power to aircraft
Secondary purpose - To start the aircraft
2 most common secondary aircraft batteries?
- Sealed lead acid
- NiCad
Methods to keep batteries held in position during flight?
Hold down points manufactured into the lid of the battery case lid: Used to secure into battery tray or aircraft frame
No hold down points available: Positioned using brackets
Lead acid batteries are made up of what components?
- Battery case
- Connectors
- Cells
Cells in a lead acid battery are made up of what components?
- Plates (pos and neg)
- Separator
- Electrolyte
How many cells are found in a lead acid battery?
How much are each cell worth?
- 12 cells
- 2v DC each
The capacity of a battery is measure in what?
Ampere-hour (Ah)
What is a C1 rating?
Amount of current that a battery can supply flat out for 1 hour
How many cells are found in a NiCad battery?
How much are each cell worth?
- 20 cells
- 1.2v each
How are the cells in a NiCad battery joined together?
- Linked in series
- Nickle plated copper used to interlink the cells
Define thermal runaway?
- Uncontrollable increase in the temperature of a battery
- Leads to discharge or toxic fumes or ignition
High temp / high changing rate = battery becomes unstable
What is SOC?
‘State of charge’
- Monitored to maintain the health of an aircraft battery
At what temp does the WMC illuminate the ‘batt temp’ warning light?
71 degrees celcius +/- 2.8 degrees celcius
What is a TRU?
Transformer rectifier unit
A TRU provides a source of what type of power?
DC power
Components of a basic TRU?
- 3 phase full rectifier
- Cooling circuit
- 3 phase transformer
- Filter unit
- Over temp warning switch
What does a voltage regulator do?
Regulate DC voltage
3 types of voltage regulators?
- Carbon pile
- Vibrating point
- Transistor
How is a voltage regulator connected?
Parallel
What is the purpose of a reverse current relay?
To stop back current damaging the generator by returning to the generator on engine shut down
3 basic busbars?
- Non-essential
- Essential
- Vital / Emergency
Under a generator fail situation, which busbar will become offline first and what components disengages it?
- Non-essential
- Relay is de-energised (GCB)
What are the 2 DC disruption systems?
- Split bus
- Tied bus (parallel)
Under a generator fail situation which component in a split bus links the no.1?
Bus tie relay
What component in a tied bus ensures the generators are sharing the load?
Equalising voltage controller
Advantage of a tied bus system compared to a split bus system?
- Voltage is always constant / 28v across the bus bar regardless of how many generators are lost
What is the purpose of an inverter?
Converts DC to AC
2 classes of inverters?
- Rotary
- Static
Advantages of a static inverter?
- No moving parts
- Light weight
- Smaller in size
Static inverter output?
115v AC
Components of a static inverter block diagram?
- DC input
- AC output
- Square wave generator
- Power amplifier
- Sinewave shaping network
Purpose of a GCU?
- Control frequency
- Regulate voltage
What is a GCU?
Generator control unit
Fundamental requirements of an AC tied bus system?
- Gens have to be in synch before they are tied together
- Gens must be maintained in synch while in use
How are the generators synchronised in an AC tied bus system?
ELMS
In an AC tied bus system with 4 generator, if generator 4 fails, what will happen?
- GCB4 will open breaking the circuit to generator 4
- Gen 1, 2 and 3 will supply power to bus 4 (will remain closed)
In an AC tied bus system with 4 generators, if generators 2, 3 and 4 fail, What will happen?
- GCB2, GCB3 and GCB4 will open, breaking the circuit to generator 2, 3 and 4
- Gen 1 is not capable of powering itself and 3 other generators on its own, therefore bus 2, 3 and 4 will remain disengaged
What is ELMS and what does it do?
Electronic load management system
- Controls all the switches
3 sources of external DC power supply in an aircraft?
- Battery
- DC generators
- TRU
Are primary batteries rechargable?
No, only secondary batteries are
Where are primary batteries used in an aircraft?
- Cockpit voice recorder (CVR)
- Flight data recorder (FDR)
- Emergency locator transmitters (ELT)
- Life vest lights
When do we service primary batteries?
Specific maintenance schedule as dictated by the equipment / aircraft manufacture
Requirements of a secondary battery?
- Large temp variation
- Pressure variation
- Cope well with inversion, vibration and impact
Why is nickle cadimum a popular choice in aviation?
- Good starting current
- Deliver a linear output
- Handle extreme temps reasonably well
- Maintenance is simplified as you can open the case and replace individual cells without having the replace them all
Name of the quick release NiCad battery connector?
Elcon style connector
Major danger regarding NiCad batteries?
Thermal runaway
2 common forms of protection for DC circuits?
- Current limiters
- Reverse current relay
How is a non essential bus isolated during failure of a primary power supply?
Load shed
Why is a current limiter used?
Reduces the generator output voltage whenever the maximum safe load is exceeded
What is the vital bus directly connected to?
- The aircraft battery
- This ensures power is supplied to the aircrafts emergency loads at all times
How is an essential bus isolated and then reconnected?
- By turning the battery switch off
- By turning on the switch
Where are split bus commonly used?
Commonly used in light aircrafts with 2 generators
Advantages of the tied bus bar?
- Tied together in parallel
- Load is distributed evenly between the aircraft generators, not supplied by an individual generator
Difference between split bus and tied bus?
Split - Series
Tied - Parallel
What does the equalising voltage controller do?
It ensures that the load carried by the generators is shared evenly
What must the voltage be within for the equalising voltage controller?
28v DC
+/- 0.5v
When will the non-essential bus be automatically load shed?
When the DC generator fails
What are we inspecting when inspecting main and emergency batteries?
- Examine physical damage (to metal enclosed batteries)
- Check for tripped circuit breakers
- Check quick disconnect plugs
- Check cables for damage, defects, security and cleanliness
When inspecting a starter generator, what are we looking for?
- Mounting bolts are tight
- Mounting bolts are lock wired if required
- Free of foreign objects
- Secured and positioned correctly
When inspecting power relay boxes, what are we looking for?
- Check security of mounting
- Examine looms, harnesses for correct bend radius and routing
- Signs of over heading
- Terminals are secured, correctly fitted and free of foreign objects
2 types of inverters?
- Rotary
- Static
Why are inverters required?
Emergency power supply for essential AC loads
What are inverters used for?
Convert DC to AC
Required AC voltage and frequency used for aircrafts?
115v
400Hz
TRU is used to charge what?
- Batteries
- Supply power to DC systems if needed
2 components that make up a rotary inverter?
- DC motor
- AC generator
What controls the frequency in a rotary inverter?
Speed of rotation of the DC motor
Components of a static inverter?
- Diodes
- Transistor
- Capacitor
- Transformer
Advantage of a static inverter over a rotary inverter?
- Light weight
- No moving parts
- Less maintenance
3 types of voltage regulators?
- Vibrating point (Sparking - overcomes spring tension, 50-200 times a second - feedback path is through the resistor)
- Carbon pile (Carbon wears down)
- Transistor (electronic switch connected to an earthing point so when the contact open and close it stops the return path)
What parts of the aircraft run off the non essential busbar?
- Toilet
- Coffee machine
- Anything that is not needed to fly (luxuries)
Problem with split bus
Lots of wires and relays
Advantage of tied bus
Less moving part, moving in parallel, constant volts
What parts of the aircraft are connected to the vital bus?
- Flight controls
- Ejecto seato
- Fire suppressant
If you are lost or stuck when troubleshooting, what do you do?
Speak to your supervisor, SPO or SME
Where are regulatory requirements for maintenance found?
- Defence aviation safety regulation (DASR)
- Military aviation regulations (MILAVREGs)
- Technical airworthiness regulations (TAREGs).
What should be followed when carrying out troubleshooting?
Repair and overhaul manuals
What must be carried out after a component is removed or disconnected?
Op test of system
Where can the periodic maintenance be found?
Technical maintenance plan (TMP)
When inspecting a static inverter what would you be looking for?
- Inspect it for signs of overheating, security, damage, or defects
- Pay attention to sign of contamination around the vent holes
- Inspect the receptacle for signs of damage, corrosion and foreign objects
How does a static inverter operate?
They go through a square wave generator, power amplifier, sine wave shaping network and then are monitored through feedback
For a static inverter, what is monitored at the feedback stage?
- Voltage
- Frequency
- Current
Components of the aircraft diagram for a split bus system?
a) External power relay
b) Auxiliary power relay
c) GCB (Generator control breaker)
d) INV (Inverter)
e) TRU 1 (Transformer rectifier unit)
f) TRU 2
Electrolyte found in a sealed lead acid battery?
Sulphuric acid combine with distilled water
What is cold cracking amps of a lead acid battery?
30 seconds at -18 degrees c
(rating and differ from 300A to 1000A depending on the aircraft)
Electrolyte found in NiCad battery?
30% potassium hydroxide / 70% distilled water
Connector used for lead acid batteries?
MIL Spec
What does the capacity of a battery depend on?
- Area of plate in contact with electrolyte
- Quantity and specific gravity of electrolyte
- Type of separater
- General condition of battery
- final limiting voltage
Components of a split bus system?
- 2 IDGs
- APU
- GCU
- TRU
- Static inverter
- External power supply
- GCB
- Bus tie breaker
