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Switch in "Jurassic Park"

Discussion in 'Electronic Design' started by [email protected], Jul 2, 2006.

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  1. Guest

    Hi.

    I just saw the movie "Jurassic Park" and noticed that in order to turn
    on the main switch to the park they have to pump up a primer handle to
    get a "charge", before they throw the switch. Are there switches out
    there that have to be pumped up before they can be used? If so, what
    was being pumped?
     
  2. Luhan

    Luhan Guest

    Thats probably to make sure the switch throws really fast. You have to
    do that in order to avoid arcing, leading to rapid heating, leading to
    your ass getting blasted into the next block.

    Luhan
     
  3. budgie

    budgie Guest

    A fecking big spring. This ensured V.fast opening/closing action and avoids
    damaging or explosive arcing. (Usually there is an interlock to ensure that the
    switch can't operate until the spring compression ("charge") has reached a
    set-point.)

    Quite a standard feature on a lot of high voltage switchgear, although by no
    means universal.
     
  4. This would most likely be a circuit breaker. The spring is used to provide
    power for closing the breaker, and I think it also retains energy after
    closing so that it can trip without further charging. These are found on
    what are technically low voltage breakers, which are rated up to 600 VAC.
    Then there is "Medium voltage" up to 5000 VAC, and only above that is
    switchgear actually "High Voltage". So a cubicle with a 4000 ampere breaker
    on a 480 VAC main feeder should be labeled "Danger: Low Voltage" !

    I don't remember that part of the movie. I think most switchgear that is
    directly operable like that is 600 VAC or less. Above that I think it is
    mostly operated by means of hot sticks or remote control by means of
    solenoids or motors, usually from a bank of batteries. Some breakers have
    charging motors or solenoids, which also usually run on DC, to charge the
    internal springs. Other breakers have cranks or handles with ratchets to
    charge the springs, and smaller molded case breakers (about 800 amps or
    less), generally require brute force to charge the spring when the breaker
    is closed using the handle. That is why it usually takes more effort to
    close a tripped breaker than one which has simply been turned off manually.

    Circuit breakers are amazing devices, and are certainly more convenient and
    versatile than fuses. However, it is always a good idea to incorporate
    fuses in the protection scheme as well. A faulty breaker will often freeze
    up in its closed position, providing no protection, while a faulty fuse
    almost always just opens prematurely, and this is usually because of
    partial melting from a previous fault, or environmental factors such as
    corrosion. Also, fuses can clear faults with potential currents of 200,000
    amperes or more, and actually limit the current to a lower value by
    clearing in less than 1/4 cycle, whereas breakers often take one or two
    cycles to clear. This means much more power is dissipated in the arc of the
    opening breaker, often causing destruction of the contacts and other parts.
    "Low voltage" breakers are generally limited to 10,000 or possibly 25,000
    amperes interrupting capacity, and even within those limits often must be
    rebuilt after clearing a fault.

    I saw a film produced by Bussmann, where they showed the effects of high
    current faults being cleared by circuit breakers and fuses. With the fuses,
    in the worst case there was a quick jump of the cables and a puff of smoke
    where the fuse body ruptured. With the breaker, huge sparks (actually
    molten metal) spewed from the arc chutes, and at currents well above the
    interrupting rating, the entire breaker exploded and the conductors
    violently flew out of the enclosure, and the resulting arc was not
    extinguished until the upstream protective device shut off power. I wish I
    had access to that film on-line. It was actually an 8 or 16 mm film, not a
    videotape.

    Paul
     
  5. Guest

    Oh, so it's a safety device to prevent the operator from electrocuting
    him/
    herself. That makes sense.
     
  6. Guest

    You mean it actually kept on arcing like a welding torch?!
     
  7. budgie

    budgie Guest

    Yes, that's why there is the interlock to prevent closure until the spring is
    charged enough for a subsequent trip.
    Those rating divisions are actually not a global standard. Different countries
    have different numbers in their local (national) standards.
    Not in this country. Here LV is less than 110DC or 32VAC IIRC. So it would
    properly read "Danger: Medium Voltage"

    But that type of message is really for the non-cognoscenti.
    Quite a bit of this stuff here in Oz has pump-up springs on 6.6/11kV gear.
    There is even one brand (nicknamed "Tupperware") which uses a huuuge over-centre
    spring action with horizontal moving contacts within cylindrical shrouds on
    their 11kV (and possibly higher rated) gear. The one thing we were taught when
    operating this - apart from the gloves and flash shield - was to NEVER stand in
    line with those "cannons" ...

    And don't get me started on the old oil-filled HV shite.
     
  8. Paul

    Paul Guest

    IIRC the loose ends alternately arced to the grounded enclosure and to
    each other where the insulation melted. The main power was only applied
    for a few cycles, and mostly there was just smoke, flying debris,
    thrashing cables, and sparks. I think it was in slow motion.

    However, a friend I work with was injured once when his coworker
    dropped an uninsulated wrench across a main 480 VAC feeder during a
    circuit breaker testing job, and it apparently caused a short with just
    enough resistance to maintain a fireball for quite some time before the
    main fuses upstream finally opened. Both were badly burned, and the
    coworker who dropped the wrench eventually died. My friend saw the
    wrench drop and had just enough time to turn away, avoiding a direct
    blast to his face.

    I went on a circuit breaker testing job early in my career, and it
    seemed safe enough to pull breakers from cubicles, service them, and
    then rack them back in to the buswork while they were tripped, and only
    closing them when they were fully locked in place. However, a few years
    later, someone went to the same site, and apparently one of the stab
    clusters was loose. While racking it in, the cluster fell across the
    live buswork, and caused quite a blast. I think he survived with some
    bad burns. Technicians are usually taught to stand to the side and turn
    away when racking switchgear.

    Paul
     
  9. be labeled "Danger: Low Voltage" !
    Thre's a new requirement in the USA that all switchgear be evaluated
    for the amount of arc-flash and labeled with the minimum safe distance
    to prevent sunburn. For the really big switches, they're labeled with
    the safe distances given various kinds of protective clothing.
     
  10. Boris Mohar

    Boris Mohar Guest

  11. Rich Grise

    Rich Grise Guest

    What was being pumped was your money out of your pocket. ;-)

    It's for dramatic effect, so that there's some unknown delay as the
    monster is closing in on them.

    Cheers!
    Rich
     
  12. John  Larkin

    John Larkin Guest

    The LA power department has a big test facility, and made a film of
    their "greatest hits." It looked like the credits background of
    "Apocalypse Now."

    John
     
  13. Guest

    Oh, because it emits lots of light, UV and X-rays, right? How do you
    pull a
    switch when you have to be far away from it (what if it's outside your
    reach?
    even with protective clothing you said there's a "safe distance")?
     
  14. Jeff L

    Jeff L Guest

    I had something similar happen with a 208V 3 phase 200A panel - I was
    removing a breaker and as I took the screw out, the bakelite piece that
    holds the breakers in place when the screw(s) are not holding it, and to
    provide insulation between the phases was cracked and fell away. This
    allowed the breaker's tab to fall across 2 phases, 12" from my face.
    Apparently there was quite a deafening "BANG" when it happened. After I got
    back from the hospital (Checking my eyes, mostly for welders flash, but I
    had contacts in which may have blocked a lot of UV), where were massive
    smoke / condensed metal stains on adjacent breakers, the panel, my
    screwdriver, the tab on the breaker was half gone, and I still never found
    the screw. I also ended up with a blotchy sunburn.

    The guys installing our new 400A feed (which is fed with a shared 1200A
    transformer - lots of short circuit current available before the feeder fuse
    blows), with much upgraded wiring work on the (crude) buss box adding wires
    while *energized* without seemingly much concern. Next time I might make it
    mandatory to when work on those panels or future larger ones is done
    de-energized, or with at least some protective gear
     
  15. Greg Neill

    Greg Neill Guest

    Some impressive arcing can be found here:

    http://205.243.100.155/frames/longarc.htm
     
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