11.6 Electrical Power Flashcards
Approximately how much power do 2 and 4 engine aircraft use?
- 2 engines = 100 kilowatts
- 4 engines = 400 kilowatts
What does the electrical power system consist of and what does each part do? [2]
- Generation subsystem - produces electrical energy
- Distribution subsystem - provides to consumers
What device converts from AC to DC?
TRU - Transformer Rectifier Unit
What device converts from DC to AC?
Static Inverter
What are the 5 AC power Supplies?
- Engine driven generator
- APU generator
- External Power
- Emergency Generator
- Static Inverter
What do AC consumers mainly consist of? (3)
- Heating
- Lighting
- Mechanical equipment
What voltage is AC power provided at?
115V
What frequency is AC power provided at?
400 hertz
What batteries are used on aircraft?
Nickel Cadmium
What do batteries provide power for? [3]
- Emergency distribution
- APU starting
- Engine start
What are the 3 parts AC/DC power distribution is divided into?
- Main Power Distribution
- Essential Power Distribution
- Emergency Power Distribution
What does AC power distribution Consist of? [3]
- Main AC busses
- Power Source Switching
- Bus Tie Switching
What does a bus do and what does it consist of? [2]
- Connects the power source to all electrical consumers that use the same type of electrical power
- Consists of a low resistance electrical connection between all wires connected
What voltage does DC power run at?
28 volts
What is the definition of “main power distribution”?
Provides electrical power to all main consumers
What is the definition of “essential power distribution”?
Supplies all consumers that are essential to operate the aircraft safely
What is the definition of “emergency power distribution”?
Supplies the consumers that necessary to land safely
What are the 4 types of AC consumers?
- single phase consumers
- voltage different from 115v
- 3 phase consumers
- large loads
What must happen to large loads before any power source is switched on or off?
Large loads must be switched off prior to power on or off
What does load shedding do?
Improves the reliability of power relays and prevent overloads of power source
What are the power relays controlled by? (2)
- Generator control unit (GCU) or,
- Ground power control unit (GPCU)
When will auto switching happen?
When voltage and frequency “Ok” and no failures
What systems may fall under “essential power distribution”?
Captain navigation and communication equipment and important control and warning systems
How long does the aircrafts battery provide sufficient electrical energy?
30 minutes
What electrical energy can the battery provide in an emergency situation?
- 24v DC directly to the DC emergency bus
- 115v AC after conversion at the static inverter to the AC emergency bus
For long range aircraft, what must be installed in case of emergency?
Emergency generator
What 2 emergency generators are there?
- air driven generator
- constant speed motor generator
What are the main distribution components? (3)
- power relays used as switching devices
- circuit breakers and fuses
- Current transformers
What 2 types of powers relays are used for AC switching?
- Contactors
- breakers
What is the main function of a fuse or circuit breaker?
To prevent an overheat or fire due to a short circuit
What happens to a fuse if the current exceeds the maximum allowed value?
The metal strip melts and electrical circuit interrupted
What are the two advantages of circuit breakers over fuses?
- reset quickly
- used as manual on/off switches to allow for deactivation of circuits
What do regulations specify about the location of circuit breakers for essential loads?
Should be within reach of the pilots during flight
What colour collars are used to identify circuit breakers for specific activities? (Crew and maintenance)
- orange (crew)
- grey (Maintenance)
What can be used to prevent a circuit breaker being closed because of a missing component?
Red safety clips
What can be used to stop circuit breakers being closed during maintenance procedures?
Red safety tags
What does circuit breaker monitor help with?
Identifying a tripped circuit breaker via a caution message on the ECAM
What are the two methods of AC power generation?
- generator
- static inverter
How does a basic generator work?
With a rotating magnet, producing a magnetic field inducing voltage in the coil of the stator, (induction with motion)
In a generator, what does the amount and polarity of generated voltage depend on?
The angle of the rotating magnet
What is one complete rotation of the magnet equal to?
One complete sine wave
How is the frequency of a generator influenced?
By the rotational speed of the magnet, and the amount of pole pairs
What does 3 phase stator coils generate?
Individual voltages
What keeps the output voltage and frequency from the engine to the generator, constant?
Constant speed drive
What components does a constant speed drive consist of? (3)
- Differential gear
- hydraulic motor/pump combination
- speed control circuit
How is the constant speed drive or integrated drive generator mounted on the engine gearbox?
Quick attach and detach rings
What do TRU’s convert?
3 phase 115v AC to 28v DC
What does the number of batteries required depend on?
The amount of electrical energy that needs to be stored
What are the advantages of using nickel cadmium batteries over lead acid type batteries?
- Less maintenance costs
- Low temperature performance
On average, how often must the battery conditions be check?
Approx every 2000 operating hours
What does a battery condition check contain? (2)
- Storage capability
- electrolyte condition
What are the advantages of lithium-ion batteries over nickel cadmium? (6)
- high voltages and high current production
- improved power quality
- ability to recharge quickly
- weigh 30% less
- compact size
- no memory degradation
How many stages does li-ion batteries charge in? And what are they?
3 stages
- constant current
- balance
- voltage source
What does the constant current charge stage do for li-ion batteries?
Charger applies constant current at a steadily increasing voltage until voltage limit reached for each cell
What does the balancing stage of charging for li-ion batteries do?
Reduces the current whilst the state of charge for each cell is brought to the same level until the battery is balanced
What may an overcharged or overheated li-ion batteries suffer from?
Thermal runaway or cell rupture
What methods can ground power be supplied? (2)
- External power source
- apu generator
What are the two types of external ground power?
- fixed station
- moveable cart
What does the plug of a receptacle consist of?
- 4 thick pins (to provide the connection for 3 phase and a common neutral)
- 2 shorter pins (control the connection)
When de-energising the aircraft from external power, what must be checked? (3)
- Electrical loads to a minimum
- consumers switched off as they will switch to battery power
- main battery switches and emergency power switches off
What bus does external power use?
Ground service bus
What does the ground service bus supply?
Equipment for loading/unloading, cleaning and cabin and cargo doors
What is the only power source during towing?
Battery
