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POWER GEN MDT2

M L English 95 cards

POWER GEN MDT2

Cards in this deck (95)

  1. 1Electrical Power Systems SourcesEngine AC generators/alternators.
    Engine DC generators/alternators.
    Batteries.
    Auxiliary Power Unit (APU).
    Air Driven Generator (ADG).
    Transformer Rectifier Unit (TRU).
    Inverters (rotary & static).
    Ground Power Unit (GPU) (external power).
  2. 2SOME AIRCRAFT LIKE turbine helicopters, small turbine aircraft HAVEA COMBINATION STARTER GENERATOR
  3. 3RELAYS ,SOLENOIDS & CONTACTORScontrol, regulates, and protect the power electrical systems, and ensure that power is provided to the right loads, at the right time, at the right voltage, capacity, phase, and frequency.
  4. 4As it relates to power distribution, breakers (GB, GCB, and BTB) are relays that can handle high current loadsAND are automatically activated by the control system or manually activated by the aircrew.
  5. 5Electrical Power Systems LoadsAvionics systems.
    Instruments.
    Anti Ice systems.
    Cooling fans.
    Engines.
    Hydraulics.
    Fuel systems.
    Anti-skid systems.
    Clocks.
    Flaps.
    Motors.
    Lighting (interior & exterior).
    Fire protection systems.
    Service outlets (115 VAC, single phase).
    Pitot static systems.
    Indicators.
    Galley equipments.
    Starters.
    TRU.
    Inverters.
    All electrically operated equipments.
  6. 6Electrical Power Systems Starter SystemElectrical Power Systems Starter System
  7. 7LARGE AIRCRAFT USESthe split bus, parallel bus, or the split-parallel bus system.
  8. 8The split bus is typically found on twin enginewith each engine having a generator, each providing AC power to its respective bus and associated loads.
  9. 9THE GENERATORonly powers one bus at any given time
  10. 10The Bus Tie Breaker (BTB)is a relay which provides isolation between the busses and could be used during a generator failure.
  11. 11The Generator Breaker (GB)is a relay which is activated to isolate or connect the generator from or to the rest of the distribution system
  12. 12GEN 1 & 2 OPERATEindependently from each other
  13. 13DURING A GENERATOR FALIURE WHAT IS USED AS A BACK UPAPU
  14. 14EXTERNAL POWER IS PROVIDED BYGround Power Unit (GPU) cart or the hangar power system
  15. 15The parallel bus systemtypically found on aircraft with 3 engines.
  16. 16In the event of a generator failurethe failed generator would be isolated from the bus by its Generator Control Breaker (GCB).
  17. 17the Split Parallel system, which is a combination of the first 2,IS typically used on 4 engines aircraft.
  18. 18Generators are connectedin parallel, thus Voltages, Frequencies, and Phases must be controlled within very strict limits, to ensure proper system operation.
  19. 193 TYPES OF POWER DISTRIBUTIONESSENTIAL(required for the safe operation of the aircraft.
    flight controls, avionics, hydraulic, instruments, etc) ,
    UTILITY(, required for the operation of the aircraft remaining systems.
    galley, entertainment system) & EMERGENCY(, used in the event of a complete electrical generator failure:
    flight controls, VHF, stand by instruments, transponder, etc…
  20. 20In an emergency scenario, the battery’s capacity is typically expected to provide30 MINS OF POWER
  21. 21an AC power generating systemsupplies 115/200 VAC, 3 phases, at 400 Hz.
  22. 225 main sources of AC power is available.5 main sources of AC power is available.
  23. 23The AC power is provided byEngine Generators, Auxiliary Power Unit (APU), Air Driven Generator (ADG), and the Ground Power Unit (GPU).
  24. 24GCUGenerator Control Unit (monitors and controls voltage and current characteristics).
  25. 25LCTALine Current Transformer Assembly (sensor used to monitor the generator current load).
  26. 26GLCGenerator Line Contactor (relay used to feed power to the right circuits).
  27. 27GTCGenerator Transfer Contactor (relay used to transfer power to the right circuits, when 1 generator fails).
  28. 28TCTATransfer Current Transformer Assembly (sensor used to monitor the current load passing through the transfer contactor).
  29. 29The DC power (4 sources) is mainly derived from the AC system, using the TRUs.The DC power (4 sources) is mainly derived from the AC system, using the TRUs.
  30. 30Transformer Rectifier Units (TRU)converts AC into DC
  31. 31The aircraft is equipped with 2 Ni Cad batteries (main & APUused for APU starting, fueling, and back-up in an emergency situation.
  32. 32Electromagnetic Inductiona magnetic field is used to induce a voltage into an adjacent circuit, IN GENERATORS
    is the action that causes electrons to flow in a conductor, when a conductor moves across a magnetic field or a magnetic field moves across a conductor.
  33. 33Whenever there is relative motion between a conductor and a magnetic fieldan EMF will be induced into the conductor and current will flow into that conductor.
  34. 34Conventions:Current flows from Negative (-) to Positive(+).
    The direction of flow of the flux lines of a magnet is from North to South.
  35. 35The generator left-hand rule can be used to determinethe direction of the induced EMF.
  36. 36LEFT HAND RULEthe index of the left hand is pointed in the direction of the magnetic lines of flux(north to south).
    the thumb is pointed in the direction of movement of the conductor through the magnetic field.
    the middle finger points in the direction of the induced EMF.
  37. 37The AC generator consists OFa Magnetic Field,
    an armature,
    Slip Rings,
    and Brushes.
  38. 38The magnetic field induces a voltage into the armature, which causes a current to flow into the loop to the load, via the slip rings and brushescurrent flow: loop > slip rings > brushes > load
  39. 393 PHASE GENERATORSseparated by 120 degrees
  40. 40exciter field coil(typically powered by a DC voltage),which generates a magnetic field
    PRIMARY
  41. 41armature coilaffected by the magnetic field and develops a strong induced voltage, which causes a current to flow out to the split rings.
    The armature is the output coil, which supplies power to the electrical power systems, specifically, the AC Bus.
    SECONDARY
  42. 42ALTERNATORSTATIONARY ARMATURE
  43. 43GENERATORROTATING ARMATURE
  44. 44PRIME MOVERsystem that turns the rotor (eg: engine).
  45. 45Exciter Field Winding/Coilconductor used to produce the magnetic field (the primary).
  46. 46Armature Winding/Coilconductor in which an EMF is induced into (the secondary)
  47. 47Statorstationary housing assembly containing a stationary winding/coil
  48. 48ROTORrotating assembly inside the stator, containing a winding/coil, where the shaft is attached to the prime mover
  49. 49The non-rotating armature is typically found inhigh power rating generation system of large aircraft.
  50. 50Large aircraft usually have their alternators driven by a shaftconnected to the gearbox.
  51. 51Permanent Magnet Generator (PMG)developed to eliminate slip rings arcing and brushes wear, in high power AC generator
  52. 52Electromagnetic inductionused to transfer power from the stationary to the rotating components.
  53. 53GCUGCU: Generator Control Unit.
  54. 54Constant frequency generator drive systems are used tomaintain accurate rotation speed of a generator.
  55. 55It is especially important to maintain a constant frequency, within close limits, when2 generators are operating in parallel.
  56. 56CSDCONSTANT SPEED DRIVE
  57. 57A CSDs drives the AC generator, which produces A3-phase 115 VAC at exactly 400 Hz.
  58. 58In order to produce a voltage at a constant AC frequency, a generator needs tospin at a constant specific RPM (typically between 6,000 to 12,000 RPM).
  59. 59CSD IS NEEDED BECAUSEthe engine speed varies from idle to full power
  60. 60The CSD takes the variable speed output of the accessory drive gearbox and hydro-mechanically produce aconstant output RPM, regardless of the fluctuation in engine speed.
  61. 61IDGINTEGRATED DRIVE GENERATOR
  62. 62The IDG is comprised ofboth a CSD and generator sealed in the same housing/casing.
    This concept reduces both the weight and the size of the 2 unit system.
  63. 63CSD/IDGoil cooled, therefore oil level must be checked regularly through the “sight glass”, and the level adjusted as required.
    Mounting hardware should be torqued using “cross” pattern technique.
    .
  64. 64RATRAM AIR TURBINE
    A constant speed propeller drives a gearbox that rotates a generator.
  65. 65ADGAIR DRIVEN GENERATOR
    The ADG deploys automatically in flight or manual in the event of a failure of the auto-deploy system.
    115VAC, 400 Hz, 15-30 kVA to the ADG bus, which is typically applied to the AC ESSENTIAL bus.
    The ADG may only be stowed on the ground.
  66. 66The emergency generation system provides AC power in flight, in the event oftotal loss of all primary and secondary AC power systems.
  67. 67INVERTERis a device for converting DC into AC, usually 26 VAC or 115 VAC, both at 400 Hz.
    Inverters are used on large aircraft for emergency power
    Many small aircraft, which utilized a DC electrical system, requiring a relatively small amount of AC power, uses inverters during normal operating conditions.
  68. 682 TYPES OF INVERTERSROTARY & STATIC
  69. 69The rotary section of the inverter consists of aDC motor driving a AC generator
    The rotor of the motor and generator are mounted on the same shaft.
    A fan is mounted on the shaft to provide for air cooling.
    The box on the top of the inverter controls the inverter’s AC output.
    These inverters are heavier than static inverters and typically require more maintenance, due to moving parts.
  70. 70The input voltage is between 26 to 29 VDC, with athree phase output of 115 VAC, at 400 Hz.
  71. 71Static inverters are very reliable, low maintenance, efficient, small, and lightweight, as compared to rotary inverters, given that they are made ofsolid state components and have no moving parts.
    The oscillator is responsible for the correct frequency output of the inverter.
    The input voltage is 14 or 28 VDC, with a three phase output of 115 VAC, at 400 Hz.
  72. 72Most transformers are eitherSTEP-UP(eg 2:8) OR STEP-DOWN(eg 10:2)
    The factor that determines the type is the “turns” ratio.
    The turns ratio is the ratio of the number of turns in the primary winding to the number of turns in the secondary winding.
  73. 73By using commutator contacts instead of slip rings,the output of the generator is now pulsating DC
    Although the current reverses its direction in the loop of the armature, the commutators action causes current to flow in the same direction.
    The generator left-hand-rule, still applies.
  74. 74The armature rotates onthe shaft held by bearings located in the generator’s end frame assembly.
    It consists of wire coils wound around a laminated soft-iron core, which is connected to the commutators.
    As the armature assembly rotates within the magnetic field, current is induced in the windings/coils.
    The windings are connected to the segments of the commutator ring, which will deliver the output current to the load, by means of carbon brushes.
  75. 75Brushes ride the surface of the commutator and act asthe electrical contact between the armature coils and the external circuit.
    A flexible braided-copper conductor, referred as “pig-tail”, connects each brush to the external circuit.
  76. 76Brushes are made ofhigh-grade carbon and are held in place by spring-loaded brush holders that are insulated from the frame.
    Carbon brushes are spring loaded to ensure constant surface contact with the commutator.
    The brushes are free to move up and down in their holders so they follow any irregularities on the commutator’s surface.
  77. 77a low spring tension can result inarcing between the commutator and the brushes, causing pitting on the commutator..
  78. 78Residual MagnetismAny material, such as field coils, that was magnetized will retain a certain amount of magnetism
    This residual magnetism makes it possible for a Gen to produce power without exciting the field from an outside source of magnetism.
    In DC generators, the field coils may be energized by current from the generator output (self excited/sustaining, no voltage from the battery).
  79. 79Should the residual magnetism be lost in the exciter coilsthe armature will not produce an output, when it starts to rotate.
    The lost of residual magnetism is typically due to exposure to excessive heat or mechanical shock, and when a generator has been out of service for an extended time.
    It can be restored by passing a DC current through the field coils, which is referred to as “flashing the field”.
  80. 80DC alternators produces AC usingslip rings, which is then internally rectified by six diodes to produce DC
    The primary components are the rotor, the stator, brush assembly, slip rings, and rectifier
  81. 81The alternator has rotating poles (field coils), which induced anEMF into a fixed stationary coil winding (armature).
    The alternator consists of a wire coil wound on a iron spool between 2 heavy iron segments with interlacing fingers, which forms one pole of the rotating magnetic field.
    As the rotor turns, an EMF is induced into the stationary stator coil windings.
  82. 82starter generatorActs as a starter motor during engine start-up and become an engine driven generator once the engine is running.
    The generator section of a starter-generator, works similarly as per a typical generator, and the starter is basically constructed the same as an electric motor.
    Advantages are that only 1 unit is required instead of 2, and that only one drive gear mechanism is required for both modes, reducing both space and weight.
  83. 83TRUconvert AC into DC, which is very similar to DC power supply.
    Typical input is 115 VAC with an output of 28 VDC.
  84. 84TRUTransformer Rectifier Units
    The TRU has a transformer with a primary winding, which is connected to the AC Bus.
    The secondary winding steps down the AC to certain level.
    A rectifier circuits is coupled to the secondary circuits for rectifying the AC power into DC power.
    A filter (capacitors) is connected to the output of the rectifier.
    When the output of the TRU is AC, this represents a failure of the rectifier diode section.
  85. 85A switch is a device forclosing (0 ohms) or opening (infinite resistance) an electric circuit.
  86. 86A solenoidis simply a high current capacity electromechanical switch, which is controlled by a small current switch.
    Eg: starter relay, battery relay, etc…
    When closed, a small current flows from the master switch, which energizes the coil, creating a magnetic field, which pulls the iron core down and the main contacts down, which provides voltage from the battery to the loads.
    They are also referred, generally, as relays and contactors.
  87. 87Efficient operation of electrical equipment in an aircraft depends ona constant voltage supply from the generator.
  88. 88The only factor that can controlled the output voltage of a generator isthe strength of the exciter field current.
  89. 89When the rheostat in the field circuit is set to increase the resistance in the field circuit,less current flows through the field winding, and the strength of the magnetic field in which the armature rotates, decreases.
    Consequently, the output voltage>current of the generator decreases.
    If the resistance in the field circuit is decreased with the rheostat, more current flows through the field windings, thus the magnetic field becomes stronger.
    Consequently, the output voltage>current of the generator increases.
  90. 90CURRENT LIMITERa device is installed that will reduce the generator current whenever the maximum safe load of the generator is exceeded.
    The Current Limiter is designed to protect the generator from loads that will cause it to overheat and eventually burn the windings insulation and windings themselves.
  91. 91Reverse Current Cut-out RelayIn every system in which the generator is used to charge batteries as well to supply operating power, an automatic means must be provided for disconnecting the generator from the battery when the generator voltage is lower than the battery voltage.
    If this is not done, the battery will discharge/drain through the generator and may burn-out the armature winding.
    The contact points are held opened by a spring, when the generator voltage is too low, and closed when the generator voltage is higher. This is enabled by the Voltage Coil to have enough current to create a magnetic field that will overcome the spring tension.
    When the battery voltage is higher than the generator voltage, current flow to the generator from the battery and the current coil magnetic field opposes the voltage coil, and the relay opens.
  92. 92Solid State Voltage RegulatorLight aircraft fully solid state voltage regulator, which regulates the voltage and provides current limiting.
    Has no moving parts and is extremely reliable as opposed to the mechanical type.
    The Zener diode sets the regulating voltage to a steady 14 VDC output from the alternator, which is initially set at the factory.
    The output voltage ca be adjusted, using R5, which changes the base voltage of Q2 (TR2).
  93. 93BPCUBus Power Control Unit
    A centralized mean of controlling the power is essential and is provided by a solid state
    In this way, when a generator fails, the appropriate GB, BTB, or TBR, is set to the correct position.
    Conversely, in the event of a system overload, the BPCU reduces the electrical load to an acceptable level by load shedding.
    For example, the galley power and the PES would be the first non-essential loads to be taken off-line.
    This power manipulation must take place within fraction of a second, to ensure uninterrupted flight.
    The BPCU receives data from the sensors and the AC Bus, and when abnormal conditions exits, makes decisions regarding the power system configuration, such as closing or opening a GB.
  94. 94Force Acting on a Wire – Both Field & CurrentThe wire is always pushed away from the side where the field is strongest.
    If current flow through the wire were reversed in direction, the two fields would add at the top and subtract at the bottom, thus since a wire is always pushed away from the strong field, the wire would be pushed down.
  95. 95Right Hand Rule for MotorsThe right-hand rule for motor rule can be used to determine the direction a current carrying wire will move in a magnetic field.
    If the index finger of the right hand is pointed in the direction of the magnetic field
    and the middle finger in the direction of current flow,
    the thumb will indicate the direction the current carrying wire will move.

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Flashcards on POWER GEN MDT2, created by M L on 20/09/2020.
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