Main forms of electrical power found on aircraft

Main forms of electrical power found on aircraft

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  • 28V DC
  • Direct current
  • Maximum current limited to 400 A due to practical DC generator and contracts arcing limits
  • Hence, max power limited to 12 KVA per channel
  • Widely used to power DC motor
    • Suitable for intermittent and reverse operations (easy to turn on and off)
    • E.g. Fuel system control valves, flap and slat lead screw liner actuators
  • Used for low power aircraft lighting (e.g. Cabin), and low power heating and cooling applications
  • Used to charge battery

  • Main forms of electrical power found on aircraft

    • 115 V AC
    • Advantage of AC over DC: 
      • smaller losses, as there is a lower current,
      • Easy to change from low to high voltage
      • And from high to low current
    • Alternating current, 400 Hz
    • Max power up to 100 K VA per channel - a lot more power
    • 3 phase supply
    • Used to power induction motors
      • Suitable for continuous single direction operation - disadvantage ,only goes at one speed in one direction, e.g. Air conditioning
    • Used for high power heating
      • E.g. Anti-ice and de-icing, gallery services, air-con
    • Used to power many avionics systems
      • E.g. Weather radar, cockpit displays, in flight entertainment
    • 26 V AC used for high power external lights

    • Power generation

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        • DC
          • Voltage induced by rotating electromagnets
          • Known as a DC generator
          • AC converted to DC by means of a commutator to achieve half rectification
          • Output smoothed using capacitors leading to a DC voltage with some ripples
        • AC
          • Voltage induced by rotating permanent magnet or electromagnet
          • Known as an alternator
          • Slip rings used instead of commutator - mechanically simpler
          • Older aircraft alternators run at a constant frequency of 400 Hz and constant voltage (CFCV)
          • Requires a constant speed shaft input, and hence complicated continuously variable transmission between prime mover and alternator
          • New systems use variable frequency constant voltage alternators
          • Mechanically much simpler and hence more reliable than CF designs, however requires additional control hardware on AC motors 

          • Primary and secondary electrical power generation systems

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              • 1. Primary power generating system
                • Power input provided by engine
              • 2. Secondary(stand-by) power generating systems; i.e. If one fails there is another power source so there is a constant voltage
                • Battery system
                • Auxiliary power unit (APU)
                • Ram-air turbine (RAT)
              • Most modern civil aircraft have three independent channels of electrical power generation - 2 primary systems, and 1 secondary system (usually APU based)
              • Critical design case is failure during an automatic landing (no avionics ... No landing) 

              • Industry perspective: aluminium wiring on the A380

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                  • Some 300 of the 500 kilometres of wiring on the A380 uses aluminium instead of the conventional copper as the current conductor, giving a 20% weight saving - wires over long distances, where weighting is important - Al is used
                  • Aluminium wiring technology has been used on all types of Airbus aircraft for wiring or cable where the cross-sectional…