ATA 24 Electric Power

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ATA 24 Electric Power

• General
• The Electric System is constructed by following
  main systems
• A. Generation System
• B. Distribution System
• C. External Power

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ATA 24 - Electric Power

• A. Generation - Generate AC/DC electric power for
  aircraft by the self contained equipment.
• Alternate Current (AC) generation consists of
• Integrated Drive Generators (IDG) on each engine
  (24-21)
• main generation (24-22)
• auxiliary generation (24-23)
• emergency generation (24-24)
• the essential generation switching (24-25)
• the control circuits for galley supply (24-26)
• the monitoring and indicating circuits for the
  cockpit (24-27)
• a static inverter which provides AC power from
  the main batteries (24-28)
• unit which control the main contactors of the
  main AC and DC generations (24-29)

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ATA 24 Electric Power

• 24-21 Integrated Drive Generators (IDG)
• Each engine (HP rotor) drives its associated IDG
  through the accessory gearbox. The drive speed
  varies according to the engine rating.
• The IDG provides a 115/200 VAC, 3-phase, 400 Hz
  AC supply at the Point of Regulation (POR).
• The IDG can be split into two parts
• the drive Constant Speed Drive (CSD),
• and the generator.
• A hydromechanical constant speed drive associated
  with a servo-valve drives the AC generator at
  constant speed.
• The GCU main functions for the regulation and
  protection of the IDG are
• regulation of the generator voltage at Point Of
  Regulation (POR),
• regulation of the generator speed,
• monitoring and protection of the system.

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ATA 24 Electric Power

• 24-22 AC main generation
• The Alternating Current (AC) main generation is
  provided by the Integrated Drive Generator (IDG)
  generators. Each IDG generator channel is
  monitored and controlled by the associated
  Generator Control Unit (GCU).
• The AC main generation enables supply of the
  whole aircraft electrical system in normal
  configuration.
• The transfer circuit controlled by the Electrical
  Contactor Management Units (ECMU)s enables the
  supply of
• all the AC electrical network or,
• half of it, depending on the availability of the
  following power sources IDGs, Auxiliary Power
  Unit (APU) generator, External Powers

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ATA 24 Electric Power

• 24-23 AC auxiliary generation
• The AC auxiliary generation is provided by the
  APU generator. The APU generator is able
• to replace a ground power unit or one, two, three
  or all the engine generators in case of
  disconnection or failure, i.e the APU generator
  system can supply each or all busses.

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ATA 24 Electric Power

• 24-24 AC emergency generation
• The AC emergency generation which consists of the
  HEGS (Hydraulic Electrical Generating System)
  enables to restore part of the distribution
  network in case of loss of AC main busbars.
• The HEGS is composed of the following items
• the hydraulic Constant Speed Motor (CSM),
• the AC generator,
• the Generator Control Unit (GCU).
• The CSM is supplied by the hydraulic circuit
  which is powered
• either by the hydraulic engine driven pumps in
  case of the loss of all main generators, the APU
  GEN being inoperative or in case of the loss of
  main busbars,
• or by the Ram Air Turbine (RAT) pump in case of
  loss of all engines or loss of specific engines /
  main busbars combination

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ATA 24 Electric Power

• 24-2526 AC power management
• These circuits control the supply of the AC
  essential distribution network. They enable
• its normal supply in normal flight configuration,
• transfer of the supply in case of AC BUS loss.
• If the electrical loads exceed the power
  available (airplane or external), automatically
  sheds AC loads by priority until the loads are
  within the capacity of the airplane or ground
  power generators. The load shedding is galleys
  first, then utility busses. Utility busses are
  followed by individual equipment items powered by
  the main AC busbar.

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ATA 24 Electric Power

• 24-28 static inverter
• The static inverter provides a source of
  alternating current when only the batteries are
  available.
• It transforms the direct current voltage into a
  single phase 115 VAC/400 Hz alternating current
  voltage.

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ATA 24 Electric Power

• A. Generation Generate AC/DC electric power for
  aircraft by the self contained equipment.
• The Direct Current (DC) generation consists of
• transformer rectifiers which supply the main DC
  network (24-32)
• emergency generation (24-34)
• the DC essential and normal generation switching
  (24-35)
• the monitoring and indicating circuits for the
  cockpit (24-37)
• main batteries and their associated Battery
  Charge Limiter (24-38)
• Battery DC generation (24-38)

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ATA 24 Electric Power

• 24-32 DC main generation
• The Direct Current (DC) main generation consists
  of several transformer rectifiers, include one
  Auxiliary Power Unit (APU) transformer rectifier.
  Each TR is supplied with three phase 115 VAC/400
  Hz current from the associated normal AC
  distribution network.
• Each TR transforms the alternating current into
  direct current (28 VDC).
• The main TRs supply the DC main network. The APU
  TR is used to charge the APU battery, start the
  APU and supply the APU network.

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ATA 24 Electric Power

• 24-34 DC emergency generation
• The Direct Current (DC) emergency generation
  consists of the essential transformer rectifier,
  ESS TR, and its associated contactor.
• The Essential Transformer Rectifier (ESS TR) is
  permanently supplied with three phase 115 VAC/400
  Hz either
• in normal configuration by the AC normal busbars
  or,
• in emergency configuration by the Constant Speed
  Motor/Generator (CSM/G), (emergency generator).
• The ESS TR transforms the three phase alternating
  current into direct current (28 VDC).
• The ESS TR supplies the DC essential busbars.
• In emergency configuration, the ESS TR is
  supplied by the CSM/G.
• As soon as the ESS TR is supplied, it transforms
  the 3-phase alternating current into 28 VDC.

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ATA 24 Electric Power

• 24-35 DC essential and normal generation
  switching
• These circuits control the supply of the Direct
  Current (DC) normal busbars and DC essential
  busbars.
• They enable
• the normal supply of the busbars involved in
  normal flight configuration,
• the automatic transfer in some failure conditions.

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ATA 24 Electric Power

• 24-38 Battery DC generation
• There are three batteries onboard.
• Two main batteries are used to supply AC/DC
  essential busbars when they are the only power
  source available on the aircraft. They can be
  coupled to the same busbar.
• The third battery is independent of the others
  and is mainly used to start the APU.
• Each battery is associated to one Battery Charge
  Limiter (BCL).
• The main function of the BCL is to monitor and
  control the battery contactor.
• In normal configuration the batteries are not
  coupled to the network most of the flight time.

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ATA 24 Electric Power

• B. Distribution Provide AC/DC electric power
  network to the aircraft systems.
• The AC electrical power distribution on board is
  carried out in several steps corresponding to
• Power distribution
• From the various sources towards the main AC
  busbars,
• Then, from the main AC busbars, either directly
  towards major consumers (electrohydraulic pumps,
  galleys ...) or towards the associated
  distribution sub-busbars.
• Distribution from these sub-busbars, towards the
  various AC consumers.
• The power distribution can be broken down as
  follows
• the AC main distribution with busbars as supply
  source (24-51)
• the AC essential distribution with busbars as
  supply source (24-52)
• the Circuit Breaker Monitoring Unit (CBMU)
  (24-53)
• the galley power supply distribution (24-56)

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ATA 24 Electric Power

• B. Distribution Provide AC/DC electric power
  network to the aircraft systems.
• The DC electrical distribution onboard is carried
  out through several steps
• power distribution
• from the main transformers rectifiers towards the
  main DC busbars located in the main electrical
  power center,
• from the essential transformer rectifier towards
  the essential DC busbars located in the emergency
  electrical power center,
• from the APU transformer rectifier towards the
  APU busbar located in the APU power center
  (5000VU),
• then from the main and essential busbars towards
  the associated distribution sub-busbars.
• distribution from these sub-busbars toward the
  different users.
• The whole DC distribution onboard can be broken
  down as follows
• the DC main distribution supplied from busbars
  (24-61)
• the DC essential distribution supplied from
  busbars (24-62)
• the DC refuelling distribution supplied from
  sub-busbars (24-67)

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ATA 24 Electric Power

• B. Distribution Provide AC/DC electric power
  network to the aircraft systems.
• There three types of distribution pattern
• Parallel type system load equally by all active
  generator
• Split bus system Each generator supply power to
  split bus and the bus only connect to each other
  when APU or ground power is used, or if one
  generator failed.
• Split bus parallel type mixed type

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ATA 24 Electric Power

• C. External power
• Two external power receptacles located aft the
  nose landing gear well enable the connection.
• The aircraft can then be supplied by two Ground
  Power Units (GPU).
• The ground power unit enables the supply of
• either the whole network by means of the transfer
  circuit (24-41)
• or only part of the network (ground service
  network) which comprises
• the AC ground service bus control (24-42)
• the DC ground service bus control (24-43)