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Why do capacitor bushings have strange shapes?

  1. Mar 27, 2012 #1
    The leads on giant capacitors have always looked mysterious and complicated to me. They almost look like RF cavities to me.

    Why are the bushings the shape they are?

    DIN_52NF1000.jpg
     
  2. jcsd
  3. Mar 27, 2012 #2
    This looks more like a giant HV insulator. The wavy shape (without sharp corners) is to maximize surface path length and minimize surface leakage, corona, and eventual arcing from exposure to year-round weather conditions, dust, air pollution etc.
     
  4. Mar 27, 2012 #3
    Thanks, that makes sense. Is your remark "without sharp corners" there to minimize electric field from concentrating in one area?

    Is the surface path maximization there to increase surface resistance?

    Are these brushing the same things I see on power lines and at power stations some times?
     
  5. Mar 27, 2012 #4

    jim hardy

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    Basically it's a hollow insulator with the capacitive coupling device inside.

    Observe it'll shed rain like a leaf. There will remain dry places on underside of the "rings" to maintain insulation.

    Near the ocean they get salt buildup. On foggy mornings you can hear them "sizzle". Electric company has periodically to shut down such lines and wash the insulators, unless Mother Nature provides a cleansing rain..
     
  6. Mar 27, 2012 #5

    dlgoff

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    I use to be able to tell what a transmission line voltage is by the length of their insulators.

    Pylon.detail.arp.750pix.jpg
     
  7. Mar 27, 2012 #6
    I'm confused of what the purpose of that one in the picture is even for. Is it just to hang the conductors from the tower?
     
  8. Mar 27, 2012 #7

    dlgoff

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    Yes, hanging the conductors. I probably shouldn't have posted causing confusion.
     
  9. Mar 27, 2012 #8
    No, it helped :)
     
  10. Mar 27, 2012 #9

    jim hardy

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    The little 'dumbell' things hanging from wire adjacent insulator are interesting.

    I once asked our relay folks about them. They're mechanical dampers to prevent the cables "singing" in the wind like guitar strings which fatigues them. They are tuned to line's expected mechanical frequency and i think 1/4 wavelength from insulator. They're a bundle of wires clamped loosely together so as to have friction .

    Exactly analogous to a tuning stub on electrical transmission line. no pun intended.
     
  11. Mar 27, 2012 #10
    That's pretty cool. I always like finding out if something is just there for decoration or if it is some crazy function that I am ignorant to, which I'm always worried it is.
     
  12. Mar 27, 2012 #11

    dlgoff

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    Getting a little off topic, albeit we're talking HV, they are called Stockbridge dampers.

    320px-Stockbridge_damper_POV.jpg
     
  13. Mar 27, 2012 #12

    sophiecentaur

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    They have those dampers on the vertical wires on some (old design) suspension bridges, too.
     
  14. Mar 27, 2012 #13
    That umbrella shape is used in HV lines, well for an umbrella!

    If you put a continuous shape, when the rain falls on it, you get these little streams which create a path for current to "crawl" to(because you animate the ions in water, slowly, and all that good stuff), and you can get a short circuit like that!

    So these cascades are used to break those streams, simple :)

    I asked the same question my professor when I visited 110/10 transformer station. That was the answer :D

    I call them HV mushrooms :)
     
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