Underground Cable Impedance-in Duct
Underground Cable Impedance-in Duct
(OP)
I know how to calculate underground cable impedances if they are direct buried.
What factors needs to be considered if they are run inside a Duct or RPVC conduit?
The first factor will be P( Soil resistivity) which cable is not in contact with it anymore.
The second factor that I can think of is the affect of barrier(duct or conduit) in mutual impedance calculation as the GMR is different now.
I appreciate any feedback on this subject.
Regards,
What factors needs to be considered if they are run inside a Duct or RPVC conduit?
The first factor will be P( Soil resistivity) which cable is not in contact with it anymore.
The second factor that I can think of is the affect of barrier(duct or conduit) in mutual impedance calculation as the GMR is different now.
I appreciate any feedback on this subject.
Regards,






RE: Underground Cable Impedance-in Duct
RE: Underground Cable Impedance-in Duct
Electrical Distribution System Protection book.
The book cost me $50, but you might be able to obtain a free copy from your local Cooper Power Systems sales rep.
Pirelli also has a ready-made list of duct or direct-buried cable impedances (Z1 & Zo) as well as ampacities. The U.S. factory has a different name now since Pirelli sold it to a UK company.
RE: Underground Cable Impedance-in Duct
Am I missing something? Wouldn't the impedance in duct underground be the same as the impedance in open air? Assuming that the duct is the same PVC or steel material in both cases and that the surrounding earth is non-magnetic.
The thermal ampacity and operating temperature at a given ampacity will be different, but the impedance should be the same. Right?
RE: Underground Cable Impedance-in Duct
RE: Underground Cable Impedance-in Duct
Well, according to formulas, the ground resistivity is a factor in calculating cable impedances, so impedance in air and underground would be different.
RE: Underground Cable Impedance-in Duct
RE: Underground Cable Impedance-in Duct
[IMG]http://i9.tinypic.com/47xm0aq.jpg[/IMG]
RE: Underground Cable Impedance-in Duct
RE: Underground Cable Impedance-in Duct
I have a feeing that since they are two different resistivity exists between them the Dij might be different.
Well, these are just assumptions and my understanding of the situation and the purpose of this post is to get an expert opinion.
Thanks
RE: Underground Cable Impedance-in Duct
I suppose you could take the difference in relative permeability into account. I can't find the relative permeability of soil, but it might make a difference of a few thousanths of a percent in the reactance if there were a large spacing between conductors. Between the phase conductor and the concentric neutral is insulation anyway, not air or soil.