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Litz conductor surrounded by drain wires = huge capacitance?

  1. Jun 20, 2010 #1
    this type of cable is used to transfer power underground:
    http://www.mahanson.com/images/Hendrix%20Cable.jpg [Broken]
    see the drain wires? i would think that those would be a huge problem because they are grounded and are right next to the conductor, i suppose any shielding would have this problem. the capacitance and thus the impedance of the wire must be HUGE.
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Jun 20, 2010 #2

    dlgoff

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    Would this be any different than a conductor in a conduit run?

    Have you looked at the cables specs?

    Here's their catalog: http://www.hendrix-wc.com/hendrix/pdf/hendrix_catalog.pdf" [Broken]

    Most of the cables listed have inductive reactance specifications.
     
    Last edited by a moderator: May 4, 2017
  4. Jun 21, 2010 #3

    sophiecentaur

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    Huge shunt capacitance means low impedance, afaik.
    But only a matter of pF per metre. And not a lot worse than the capacitance to the surrounding Earth if the cable is buried.
     
    Last edited by a moderator: May 4, 2017
  5. Jun 21, 2010 #4
    is that because the impedance of a capacitor is NEGATIVE -j/wc ?
    thats a little confusing because it begs the question

    which is greater
    j
    or
    -j
     
  6. Jun 21, 2010 #5
    or maybe it is the case that the inductance of a litz wire is always greater than any capacitance, so that any capacitance will counteract the inductance for a smaller impedance?
     
  7. Jun 21, 2010 #6

    sophiecentaur

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    The inductance per metre would be very very low (a series element) and the shunt reactance would be very high for such a small capacitance.

    Why should the litz wire have a large inductance? It would be the inductance of a lot of parallel inductances, surely?

    What is the intended function of the 'drain' wires apart from providing a reliable and defined path to ground if the cable gets squashed?
     
  8. Jun 21, 2010 #7
    i know these effects are small but i have to calculate them. maybe the purpose of the drain wired is to provide capacitance to counteract inductance
     
  9. Jun 22, 2010 #8

    sophiecentaur

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    But as I said, there is plenty of capacitance when the cable is underground - with or without the drain wires. The capacitative effect is more than the inductive effect - underground cables have a worse power factor than overheads.

    Use the transmission line equations and you will see what I mean.
     
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