11.6 Electrical Power Flashcards
What does the electrical power system consist of?
Generation and Distribution
What type of battery does the aircraft use?
Nickel cadmium storage
What is an Elcon connector?
Quick release battery connector
What type of wire locking is used for battery connectors?
Copper
What used to be an issue with Ni-Cad batteries?
Thermal runaway
How much does each cell of the battery produce in voltage?
1.2V
When is a cell completely discharged?
Drops below 1.0V
How often should batteries be checked in the workshop?
Every 2000 hours.
What are the two basic methods of charging?
Constant voltage or constant current.
What kind of battery is commonly charged using constant voltage?
Lead acid
What is it crucial to do when charging Ni-Cad batteries through constant current?
Monitor it due to the risk of overcharging
How long must a battery be able to provide all essential services?
30 minutes
What is the minimum capacity of a battery?
80%
What are the three different DC power sources?
DC battery
External DC power source
DC generators
What core do the brushes of the DC generator have?
Molybdenum Disulphide
What are DC generators rated in?
Volts and Amps
What is a flange mounting?
Generator is attached to an auxiliaries’ gearbox on the engine.
What is the manacle ring?
The massive ring clamp that holds the generator onto the gearbox.
What is the purpose of the TRU?
AC conversion to DC
What does PPDS stand for?
Parallel Power Distribution System
What is a PPDS?
Twin-engine or multiple-engine aircraft employ a parallel power distribution system. During normal flight conditions, both engine‑driven generators connect and power the DC loads.
What are the advantages of parallel DC operation?
TRU’s are loaded with the average current
No DC bus is lost
Why do aircraft use three phase brushless generators?
Output is constant, except in VSCF
What does the CSD do?
A device between the engines auxiliary gearbox and generator, converts the variable speed to constant.
What systems are driven by the gearbox?
Fuel/ Oil/ Hyd pumps
N2 Indication
AC generator
What does the mechanical flyweight governor keep the generator output at?
400Hz
What are the two basic types of CSD?
Variable Pitch Swashplate
Variable Gear Ratio
What is a swashplate pump?
Rotating cylinder containing pistons
What does the load control unit do?
Receives it’s electrical information from the GCU, when the output is too low it increases the load
What is the working pressure of the CSD oil?
250 psi
What does the IDG combine?
Generator and CSD
In modern AC generators where does the excitation come from?
Rotating magnet to an internal PMG
What version of generator is preferred, star or delta wound?
Star
How is AC converted to DC?
Inverter
What is a current transformer?
Three inductive pick up holes that have wires with AC going through.
What is the differential protection circuit?
Detect short circuits
What is EROP?
Extended range operation
If the RAT is deployed what does the aircraft do?
EMER GEN ON
What factors effect the magnitude of induced EMF?
Strength of the magnetic field
Number of turns in the coil
Rate of change in flux
What is the most common voltage regulation system?
Solid state
What is the purpose of a current limiter?
limit the current demanded from the generator
What is an example of an electromechanical current limiter?
Triple Unit Regulator
What happens when the shunt field current is reduced?
Flux and generator outputs fall
What is RCCO?
Reverse current cut out, also known as differential protection
How does over excitation get fixed?
The unit removes the generator from parallel
What is the main distribution point of the DC system?
DC busbar
What are the three power classifications of AC and DC systems?
Main Power
Essential Power
Emergency Power
What do busbars provide?
A way of distributing electrical power and provide a physical connection for circuit breakers.
What four types of bus bar are there?
Main buses
Sub busbars
Tie Buses
Transfer lines
What is a main bus?
carry the main power be it Alternating Current (AC) or Direct Current (DC) power from a source to sub-buses
What is the sub bus?
supply systems and sub-systems from the main buses and again are either AC or DC
What is the tie bus?
tie different sources of the same power to the main buses
What is a transfer bus/line?
allow the transfer of different sources of the same power from the main bus to the main bus
What three settings does the bus bar coupling switch have?
Auto
Man
Dis
What are VSG’s?
Variable speed generators
What is a VFG?
Variable frequency generator
What does a bus consist of?
consists only of a low resistance electrical connection between all the wires that lead to the different consumers
How is power source switching performed?
Power relays
What do all AC buses have?
Three others, A,B or C for the three phases
What is a NPBT?
No power break transfer
What is an inverter?
DC source to AC supply
What is a transformer?
Step up or down voltages
What is a rectifier?
AC to D, usually achieved by diodes
What are the two classifications of rectifiers?
Half wave
Full Wave
What two types of inverter are there?
Rotary
Static
What does a rotary inverter consist of?
DC motor, which is powered from the DC bus bar mechanically coupled to a small AC generator.
What does a static inverter consist of?
solid-state 400 Hz sinusoidal oscillator and a transformer
What are the benefits of static inverters?
High efficiency
Low cost
Quiet etc etc
What is the power factor of TRU’s?
Greater than 0.96
What is required to full wave rectify single phase AC?
4 diodes
How is AC ripple reduced?
Smoothing filter
How are circuits protected?
Fuses
Breakers
When does a short occur?
When there is a hard short between the high voltage side and the ground or different voltage potential
What categories of C/B are there?
Push/Pull
Push
Switch
Thermal
What does a green C/B mean as supposed to a black one?
It is part of the monitored system.
What does the power selector switch stop GPU’s from doing?
Charging the battery directly
