Power cable concentric neutral specs

[VLFit]

I am trying to find the data for the resistance of a concentric neutral for various common cables sizes: 15,25,35,69 kV, etc. Of course I can look up the R for #16 and do the math but there must be a stretch factor when a cable is extruded. The neutral wires must stretch and the R changes. Any help?

 

[magoo2]

There's no stretch foir the concentric neutrals. They are laid in a helical pattern which increases the distance per foot of main conductor.

 

[VLFit]

If no stretch then the only consideration is the extra length since wound helically. We have been using 10% but if there is a chart somewhere, please let me know. Any idea as to the power factor of the neutral when new, which of course should change as corrosion occurs. thanks