Litz conductor surrounded by drain wires = huge capacitance?

[chopficaro]

this type of cable is used to transfer power underground:
http://www.mahanson.com/images/Hendrix%20Cable.jpg
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.

 

[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"

Most of the cables listed have inductive reactance specifications.

 

[sophiecentaur]

this type of cable is used to transfer power underground:
http://www.mahanson.com/images/Hendrix%20Cable.jpg
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.

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.

 

[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

 

[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?

 

[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?

 

[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

 

[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.