Cable self charging

Discussion in 'General Electronics Chat' started by strantor, Oct 26, 2015.

  1. strantor

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    There exists a phenomenon which subsea ROV technicians are undoubtedly familiar with, and the only reference I have to it is translated from Dutch as "Cable self charging."

    It is a phenomenon by which a non-energized wire or cable of exceptional length (like a subsea umbilical cable) might build up a high voltage charge by means of (inductive coupling?), (antenna effect?), (capacitive effect of the dielectric insulation between conductor and jacket?). It is common practice by those who routinely terminate/un-terminate these several-km cables to use a shorting probe to discharge this "self charge" after spooling up one which has been deployed.

    I would like to know how/why this charge develops, what factors influence the magnitude of charge, and safety tips/mitigation factors for working with cables that might develop such a charge. This is for a technical/safety training program I am developing. I cannot find any scholarly articles on the topic. All my google results are for inductive cell phone charging, and this:

    [​IMG]

    If anyone here is familiar with this phenomenon and could direct me to some articles or at least provide me some keywords by which I could search them, I would greatly appreciate it.

    Thank you!
     
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  2. strantor

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  3. gerty

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  4. strantor

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  5. WBahn

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    Perhaps the same phenomenon in a different situation is the high static charges that build up on aircraft, particularly helicopters, due to their motion through the air.
     
  6. #12

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    This seems amazing. A charge builds up on a cable that is immersed in a conducting liquid???
    Keep us posted!

    Not that I plan on trying to find some submerged cables to measure, but my curiosity is at Defcon2.:)
     
  7. WBahn

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    I was wondering the same thing. I'm assuming that it is a charge on an inner layer of the cable.
     
  8. Biff383

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    I've noticed that submersibles use twisted pair conductors, I too am interested in why.
     
  9. RichardO

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    When my dad was young he would string a long wire between buildings on the farm as a radio antenna. He said that he could draw a spark from the wire when the wind blew.

    Back on topic. I wonder if the charge buildup is larger when the wire is wound and unwound from the reel.
     
  10. #12

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    Back on topic. I wonder if there is enough charge to repel sharks.
    Imagine, a proper shark-proof suit consisting of several kilometers of cable wound around a person.
    Or would the shark die of old age before he could chew through all that cable?:D
     
  11. strantor

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    I didn't get very far with my research yet (got side tracked), so I may be off base here, but now that you mention it, I think you may have just nailed it...

    "...immersed in a conducting liquid" ... conducting liquid, AKA conductor...
    a wire is a conductor surrounded by an insulator, aka dielectric.
    So, conductor --> dielectric --> conductor, we have a giant capacitor.

    As we pull this giant capacitor up out of the water, we are decreasing the surface area which is submerged in conductive liquid; we are decreasing the size of one of the plates of the giant capacitor.

    What happens when we decrease the plate size? According to the AAC E-book, the symptoms would be the same as increasing the plate spacing; Capacitance would decrease. But I think we know that if you put a charge into a capacitor and then increase the plate spacing, the voltage will increase. Assuming our giant capacitor already had some minuscule charge in it (from tribocharging or induction from other sources), I think by decreasing the exterior plate area (the length dipped in water), we multiply the charge voltage level same as if we had increased plate spacing.

    Does that sound sound?
     
  12. GopherT

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    I think you have a great big Teflon or Mylar capacitor that was charged by erosion of the insulation being pulled through a slightly abrasive media (diatoms, plankton, etc). Eroding off the insulating sheathing of the cable as it is pulled through, or pulled along the boat, or, pulled along itself as it is yanked onto the spool. That static is balanced, as you said, in the form of a capacitor on the conductive side. The tribo generated static on the insulation is the dielectric in this case.
     
  13. #12

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    Don't forget the magnetic field of the planet. Half a gauss across kilometers of cable might have some effect.
     
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