Systems 2 AC circuits

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Systems 2 AC circuits
2013-08-01 18:44:00
AC circuits

AC circuits
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  1. What is the typical AC Voltage and Frequency on large aircraft?

  2. Formula for calculating Frequency output of alternators with more than 2 poles
  3. What is the value of RMS
    RMS = 

    RMS = peak value x sin 45o   

    RMS = peak value x 0.707
  4. How does current wave compare to voltage wave
    Current LAGS voltage by 90o
  5. How is the voltage output of an AC generator controlled?
    By varying the magnitude of the current flowing to the field windings
  6. What is a CSDS and what does it do?
    Constant Speed Drive System

    Hydro mechanical differential transmission converting variable input (engine speed) to constant output (Gen) speed.

    Variable delivery hydraulic pump
  7. What is an IDG and what does it do
    Integrated Drive Generator

    • CSDS and Gen in 1.
    • Saves on size and weight
  8. What is the main difference between IDG and separate CSD and Gen systems
    Cooling method

    Instead of being Ram air cooled, the IDG is cooled by oil spray from CSD which is then cooled in a heat exchanger.
  9. Reasons for, actions after, and consequences of unacceptable fluctuations in AC supply freq from CSD
    Low Oil Pressure or High Oil Temp

    Can be manually disconnected from flight deck (provided engine is running in normal operating range)

    Cannot be re-instated in the air, only my engos on the ground
  10. What is a VSCF
    Variable Speed Constant Frequency.

    • AC gen connected directly to engine
    • Produces Freq Wild AC
    • Then rectified to DC and then fed to a static inverter to give 3 phase AC at 400hz
  11. How does a RAT work and at what RPM?
    blades drive Hydraulic pump

    pump drives hydraulic motor

    motor drives a Gen at 12,000 RPM

    produces 3 phase to power essential items and try to keep batteries charged
  12. What are the advantages of solid state inverters over older rotary ones?
    No moving parts so reliable

    Very little heat generated so low cooling needed

    No arcing at low air pressures like a rotary.
  13. how is AC fed to essential consumers if the GEN fails
    Battery DC is fed to a static converter to produce AC
  14. When is a diode rectifier unsuitable? and then what is used?
    At very high currents diodes break down

    Rotary rectifier - (AC motor driving a DC gen) "an inverter in reverse"
  15. Transformers convert what?
    AC at constant frequency

    Steps Voltage up or down, depending on number of coils of input and output winding's.
  16. What are the 2 classes of Transformers
    Voltage (power) transformers

    Current transformers
  17. What is a TRU and it's function?
    Transformer Rectifier Unit

    For converting AC and high voltage to DC at a lower voltage.

    3 phase AC is stepped down and then rectified
  18. Advantages of AC power
    AC Gens are lighter and simpler

    Lower transmission loss at high voltages and smaller diameter wire saves weight.

    Voltage can be stepped up or down easily with a transformer at almost no loss.

    DC voltage can be easily available with TRUs

    With no Commutator, AC Gens don't arc at high voltages and low pressures.
  19. disadvantages of AC
    Relies on external excitation - Unless a complex internal excitation mechanism is used

    Induced voltages cause by AC can lead to stray currents, radio interference and extra gen loads.

    AC motors have similar advantages to AC Gens, although DC motors have higher starting torques.