# Litz conductor surrounded by drain wires = huge capacitance?

1. Jun 20, 2010

### chopficaro

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. Jun 20, 2010

### dlgoff

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
3. Jun 21, 2010

### sophiecentaur

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
4. Jun 21, 2010

### chopficaro

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

5. Jun 21, 2010

### chopficaro

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?

6. Jun 21, 2010

### sophiecentaur

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?

7. Jun 21, 2010

### chopficaro

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

8. Jun 22, 2010

### sophiecentaur

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.