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400 Hz

Discussion in 'Electrical Engineering' started by Estimation, Dec 4, 2003.

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  1. Estimation

    Estimation Guest

    Why do aircraft run on 400 Hz in stead of 60Hz?

    Electrical Estimator
  2. Magetic cores (in transformers, motors, generators) can be ~1/7 of the
    weight. Weight is really important on airplanes.

    Best regards,
    Spehro Pefhany
  3. An injunction?

    Best regards,
    Spehro Pefhany
  4. True enough. The full weight of the long arm of the law. I remember
    the right answer now, but I'll let Paul tell it.

    Best regards,
    Spehro Pefhany
  5. B J Conner

    B J Conner Guest

    The synchronous speed of a 400 hrz motor is 24,000 RPM. That will make a
    good gyrocompass.
  6. daestrom

    daestrom Guest

    Not *all* 400 hz machines are that fast. RPM = F*120/ (Poles). So a 26
    pole 400 HZ motor has a sync speed of only about 1846 RPM

    We had some M-G sets for 400hz that were this many poles, driven by DC

  7. art

    art Guest

    What was the application for them?
  8. daestrom

    daestrom Guest

    To generate smooth 400 HZ for use in radar, sonar and fire-control systems.
    (i.e. military)

  9. art

    art Guest

    I red that military some where ordered 4000A DC service, you explain one of
    the possible application. But why DC driven?
  10. daestrom

    daestrom Guest

    The particular application (submarine) already had a large, DC source. The
    DC busses are more reliable than even the 'vital' AC busses. And
    variable-speed DC drive motor is pretty simple (i.e. robust) technology in
    their day.

    400HZ was also used in basic navigation equipment (like gyrocompass). The
    starboard DC bus that powered emergency propulsion, had DC diesel tie-in,
    battery-bus tie, 400HZ MG and emergency steering&diving hydraulics was
    called the 'go home' bus. As electrical operator, if I kept *that* one on,
    I knew, "well, at least we can go home."

    I'm sure there are other applications that would prefer 60HZ -> 400HZ M-G
    sets instead. My brother (civilian) recounts story of large 400 HZ/12V m-g
    (60 -> 400) that was used for computer room power supply. Something about
    rectified 400HZ was smoother to filter before such wide spread use of
    switching power supplies. (these are *old* computer rooms that are long
    gone now ;-)

  11. A+

    A+ Guest

    I've seen 60 - 415 hz frequency converters used for the good old IBM
    Mainframes but those monsters are on their way of extinction. IBM justified
    their use by : Stable / lower power consumption... Certainly smaller and
    lighter than 60 Hz equivalent where in subs or planes it is crutial.
  12. Used to work for a company which made computers for ships, and
    they often also had 400Hz supplies. We had a large 50Hz-400Hz
    converter, 300kVA IIRC, but I can't remember what voltage the
    ship based kit used. Also had large 48VDC supplies for telephone
    exchange based equipment.
  13. Jon Elson

    Jon Elson Guest

    Larger IBM 360 computers (1968-1972) used 5000 Hz, 120 V single-phase
    power to supply all the computing circuitry. They used a "converter-
    inverter" to turn 208 V 50/60 Hz 3 Phase mains power to DC, then inverted
    it with a fast SCR inverter. The 5 KHz whine was almost earsplitting
    when you walked behind the main CPU cabinet. All the modular power
    supplies in the machine ran of the roughly regulated 5 KHz power.
    They used very thin transformer laminations, and the magnetics and
    filter caps were VERY small for the day. This would apply to the
    360/50 and above.

    Large 370 mainframes used 415 Hz 3-phase power from a GE motor-generator
    set. The advantage of these was the rotary inertia in the MG set, that could
    power the machine for a few seconds when line power failed. it was pretty
    wierd to be near the machine when there was a short power blip. All the
    fans in the machine would fall silent, but the lights would keep flickering
    away on the console. They used some really inventive circuits in the
    regulators, too. They called this the electronic capacitor. It was
    a big inductor that circulated current during the line peaks. At
    the time of the dips between peaks, a transistor turned off for a
    moment, allowing the current in the inductor to be added to the
    current flowing out of the filter caps. The currents in these things
    were huge, several hundred amps from each supply at -2 and +3.3 V.
    The logic was similar to standard ECL.

  14. Jon Elson

    Jon Elson Guest

    No, 3600 RPM was fast enough for nearly all disk drives of that
    date. If they wanted it a bit faster, it would be no big deal
    to change the pulley diameters. The windage losses of 14"
    disk platters were already huge at 3600 RPM, you really couldn't
    spin a big stack of them at 10,000 RPM without reducing air pressure
    or supplying process cooling or they'd literally burn up!

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