Thermal Resistivity of Backfill Materials for Buried Cables

[redtrumpet]

A client has standardized on using a crushed limestone backfill, sieve passing 100% 6mm (1/4 inch) particles, to obtain a better heat dissipation in the vicinity of buried 15 kV cables. Unfortunately, no one seems to know the actual thermal resistivity of the limestone.

Does anyone have any data that would allow me to make a conservative estimate or educated guess as to the limestone backfill resistivity value in both wet and dry conditions? Also, does anyone have any experience with and/or data for some of the flowable grouts/cements and flyash or bentonite mixtures that are also sometimes used?

In-situ testing of the conductivity of the native soil and existing limestone backfills has been vetoed by the client as too costly.

 

[gordonl]

Try these references:

CIGRE (Dec 1992) "Determination of a value of critical temperature rise for a cable backfill material", Electra, vol. 145, pp 15-29

There is an Ontario Hydro fellow who is an expert in the field:
Dr. George Anders

I have some more references similar to above document if desired.

 

[redtrumpet]

I found the answer. There is a great web site

http://www.matweb.com

that has properties of thousands of materials.

 

[BJC]

Dry limestone has a Rho of about 120. That is when it's dry. If you have a high water table it drops. In dry years (like this one maby) It will be 120 part of the time. It only takes a week or so to burn up a cable.
If you ha choice I would recommend lean concrete backfill. You get a rho of 55 and it goes in faster.
Try this site.

http://www.nfpa.org/PDF/NecApB.pdf?src=necdigest