Aaft Elel Sys-b-9-w3-310313
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Transcript of Aaft Elel Sys-b-9-w3-310313
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Aircraft Electrical Systems
The function of the aircraft electricalsystem is to generate, regulate anddistribute electrical power throughout
the aircraft
New-generation aircraft rely heavilyon electrical power because of the
wide use of electronic flightinstrument systems
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Electrical Power Uses
Aircraft electrical power is used tooperate:
Aircraft Flight Instruments
Essential Systems
Passenger Services
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Electrical Power Uses (cont.)
Essential power is power that theaircraft needs to be able to continuesafe operation
Passenger services power is thepower that used for:
Cabin lighting
Operation of entertainment systems
Preparation of food
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Power Used
Aircraft electrical componentsoperate on many different voltagesboth AC and DC
However, most of the systems use:
115 VAC @ 400 Hz
28 VDC
26 VAC is also used in some aircraftfor lighting
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Power Sources
There are sever different power sourceson large aircraft to be able to handleexcessive loads, for redundancy, and for
emergency situations. These power sources include:
Engine driven AC generators
Auxiliary Power Units
External power
Ram Air Turbines
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Engine Driven AC Generators
Each of the engines on an aircraftdrives an AC generator
The power produced by thesegenerators is used in normal flight tosupply the entire aircraft with power
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APU Power
Most often the APUs power is usedwhile the aircraft is on the groundduring maintenance or for engine
starting
However, most aircraft can use theAPU while in flight as a backup power
sourceOne exception to this is the B272, which
only allows APU operation in the ground
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External Power
External power may only be usedwith the aircraft on the ground
This system utilizes a Ground PowerUnit (GPU) to provide AC powerthrough an external plug on the noseof the aircraft
GPUs may be either portable orstationary units
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Ram Air Turbine
Some aircraft are equipped with RamAir Turbines, or RATs
These may be used, in the case of agenerator or APU failure, as anemergency power source
When necessary, the RAT may bedeployed to be used as an AC powersource
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Aircraft Batteries
The aircrafts nickel cadmium batteryis final source of backup power
The battery provides 28 VDC
It is also possible to change the 28VDC into 115 VAC 400Hz with theuse of a static inverter
When using the battery, powerusage is limited by the short life ofthe battery
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Electrical Power System
ComponentsAC Generator
Constant Speed Drive
Integrated Drive GeneratorTransformer Rectifier Unit
Generator Control Unit
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Constant Speed Drive
The purpose of the Constant Speed Drive(CSD) is to take rotational power from theengine and, no matter the engine speed,
turn the generator at a constant speed This is necessary because the generator
output must be 400Hz
CSD Operation
The engine turns the CSD which uses adifferential assembly and hydraulic pumps toturn the generator
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Integrated Drive Generator
Another method of regulating thegenerator speed is with the use of anIntegrated Drive Generator (IDG)
An IDG is simply a CSD andgenerator combined into one unit
There are two ways to mount the
IDG:Co-axiallySide-by-side
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Transformer Rectifier Unit
Transformer Rectifier Units (TRUs) areutilized to 115 VAC, 400Hz into 28 VDC
A transformer is used to reduce the
voltage from 115 volts to 28 volts At this point the 28 volts is still AC current
To change the current from AC to DC, arectifier is used
Each aircraft AC bus feeds a TRU whichfeeds a DC bus
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Other Generator Controls and
Monitoring Devices A Generator Control Unit (GCU), or
voltage regulator, is used to controlgenerator output
Generator circuit protection monitorselectrical system parameters
Voltage
Frequency
Overcurrent
Undercurrent
Differential Fault
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Other Generator Controls and
Monitoring DevicesLoad controls sense real system load
to provide a signal to the CSD forfrequency control
Current transformers are used forcurrent load sensing and differentialfault protection
The electrical system control panelmay be found either on the pilotsoverhead panel or on the flightengineers panel
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Function of System
ComponentsThe basic functions of the electrical
systems components are to:
Generate Power
Control Electrical Power
Protect the Electrical System
Distribute Electrical Power Throughout
the Aircraft
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Aircraft Electrical Systems
The function of the aircraft electricalsystem is to generate, regulate anddistribute electrical power throughout
the aircraft
New-generation aircraft rely heavilyon electrical power because of the
wide use of electronic flightinstrument systems
-
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Electrical Power Uses
Aircraft electrical power is used tooperate:
Aircraft Flight Instruments
Essential Systems
Passenger Services
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Electrical Power Uses (cont.)
Essential power is power that theaircraft needs to be able to continuesafe operation
Passenger services power is thepower that used for:
Cabin lighting
Operation of entertainment systems
Preparation of food
-
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Power Used
Aircraft electrical componentsoperate on many different voltagesboth AC and DC
However, most of the systems use:
115 VAC @ 400 Hz
28 VDC
26 VAC is also used in some aircraftfor lighting
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WHY 400 Hz ?
Higher than usual frequencies,such as 400 Hz, offer severaladvantages over 60 Hz notably
in allowing smaller, lighter powersupplies to be used for militaryhardware, commercial aircraftoperations and computer
applications.
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WHY 400 Hz ?
As aircraft space is at a premium andweight is critical to aircraft enginethrust and fuel burn (and thus the
aircraft range and enginehorsepower per pound), 115 volts at400 Hz offers a distinct advantage
and is much better than the usual 60Hz used in utility power generation.
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WHY 400 Hz ?
However, higher frequencies are alsomore sensitive to voltage drop problems.
Reactive drops, on the other hand, are
caused by the inductive properties of theconductor. Reactive drops are a functionof both cable length and the AC frequencyflowing through the conductor. With highfrequencies such as 400 Hz, reactivedrops are up to seven times greater
at 60 Hz.
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Power Sources
There are different power sources on largeaircraft to be able to handle excessiveloads, for redundancy, and for emergency
situations. These power sources include:
Engine driven AC generators
Auxiliary Power Units
External power
Ram Air Turbines
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Typical Aircraft Electrical System
Primary (main) power source
Emergency power source Secondary power conversion
equipment
System control and protectiondevices
Interconnection network
Power distribution system
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Engine Driven AC Generators
Each of the engines on an aircraftdrives an AC generator
The power produced by thesegenerators is used in normal flight tosupply the entire aircraft with power
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APU Power
Most often the APUs power is usedwhile the aircraft is on the groundduring maintenance or for engine
starting
However, most aircraft can use theAPU while in flight as a backup power
sourceOne exception to this is the B-727,
which only allows APU operation in the
ground
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Vaughn College
APU on a stand
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Functions of APU
The primary purpose of an aircraftAPU is to provide power to start themain engines. Turbine engines havelarge, heavy rotors that must beaccelerated to a high rotationalspeed in order to provide sufficientair compression for self-sustainingoperation. This process takes
significantly longer and requiresmuch more energy than starting areciprocating engine.
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Functions of APU
Smaller turbine engines are usuallystarted by an electric motor, whilelarger turbine engines are usuallystarted by an air turbine motor.Whether the starter is electrically orpneumatically powered, however,
the amount of energy required is fargreater than what could be providedby a storage device (battery or air
tank) of reasonable size and weight
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Functions of APU
An APU solves this problem by poweringup the aircraft in two stages. First, theAPU is started by an electric motor, withpower supplied by a battery or external
power source (ground power unit). Afterthe APU accelerates to full speed, it canprovide a much larger amount of power tostart the aircraft's main engines, either by
turning an electrical generator or byproviding compressed air to the air turbineof the starter motor.
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Functions of APU
APUs also have several auxiliaryfunctions. Electrical andpneumatic power are used to runthe heating, cooling, and
ventilation systems prior tostarting the main engines. Thisallows the cabin to becomfortable while thepassengers are boarding withoutthe expense, noise, and dangerof running one of the aircraft's
main engines
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Functions of APU
Electrical power is also used to powerup systems for preflight checks.Some APUs are also connected to a
hydraulic pump, allowingmaintenance and flight crews tooperate the flight controls and powerequipment without running the main
engines. This same function is alsoused as a backup in flight in case ofan engine failure or hydraulic pump
failure.
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External Power
External power may only be usedwith the aircraft on the ground
This system utilizes a Ground PowerUnit (GPU) to provide AC powerthrough an external plug on the noseof the aircraft
GPUs may be either portable orstationary units
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Ground power
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Emergency power
In the event of a primary powersource failure, emergency poweris usually provided from
independent auxiliary power unit(APU)-driven generator(s), ramair or hydraulically-driven
generator(s), or batteries.
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Ram Air Turbine
Some aircraft are equipped with RamAir Turbines, or RATs
These may be used, in the case of agenerator or APU failure, as anemergency power source
When necessary, the RAT may be
deployed to be used as an AC powersource
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Emergency Power Source
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Aircraft Batteries
The aircrafts nickel cadmium batteryis final source of backup power
The battery provides 28 VDC
It is also possible to change the 28VDC into 115 VAC 400Hz with theuse of a static inverter
When using the battery, powerusage is limited by the short life ofthe battery
El t i l P S t
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Electrical Power System
ComponentsAC Generator
Constant Speed Drive
Integrated Drive GeneratorTransformer Rectifier Unit
Generator Control Unit
-
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Constant Speed Drive
The purpose of the Constant Speed Drive(CSD) is to take rotational power from theengine and, no matter the engine speed,
turn the generator at a constant speed This is necessary because the generator
output must be 400Hz
CSD Operation
The engine turns the CSD which uses adifferential assembly and hydraulic pumps toturn the generator
-
8/23/2019 Aaft Elel Sys-b-9-w3-310313
46/54
Integrated Drive Generator
Another method of regulating thegenerator speed is with the use of anIntegrated Drive Generator (IDG)
An IDG is simply a CSD andgenerator combined into one unit
There are two ways to mount the
IDG:Co-axiallySide-by-side
-
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Transformer Rectifier Unit
Transformer Rectifier Units (TRUs)are utilized to 115 VAC, 400Hz into28 VDC.
A transformer is used to reduce thevoltage from 115 volts to 28 volts.
At this point the 28 volts is still ACcurrent.
To change the current from AC toDC, a rectifier is used.
Each aircraft AC bus feeds a TRU
which feeds a DC bus.
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Oth G t C t l d
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Other Generator Controls and
Monitoring Devices A Generator Control Unit (GCU), or
voltage regulator, is used to controlgenerator output
Generator circuit protection monitorselectrical system parameters
Voltage
Frequency
Overcurrent
Undercurrent
Differential Fault
Oth G t C t l d
-
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Other Generator Controls and
Monitoring DevicesLoad controls sense real system load
to provide a signal to the CSD forfrequency control
Current transformers are used forcurrent load sensing and differentialfault protection
The electrical system control panelmay be found either on the pilotsoverhead panel or on the flightengineers panel
F ti f S t
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Function of System
ComponentsThe basic functions of the electrical
systems components are to:
Generate Power.
Control Electrical Power.
Protect the Electrical System.
Distribute Electrical PowerThroughout the Aircraft.
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As a engineer, we should know the
following information
Electrical system operation,which describes primary andsecondary power sources, bus
configuration with circuitbreakers and connected. loadsfor each bus. A copy of the bus
wiring diagram or electricalschematic should also beconsidered for inclusion in the
report.
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As a engineer, we should know the
following information
Alternators and other powersource description and
related data (including suchitems as battery dischargecurves, Transformer Rectifier
Unit (TRU), Inverter, APU,RAT, etc.)
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