Default Material Values
Thermal Resistivity
Below are values obtained from CIGRE, Sintef and NMBU, which should be viewed as a guide only. We always recommend that a measure thermal resistivity on the masses as local conditions affect the value.
| Mass | Wet [mK/W] | Dry [mK/W] | Source |
|---|---|---|---|
| Gravel (coarse-fine) | 0.5 | 2.5 | Cigre TB 714 (2017)12 |
| Sand (coarse-fine) | 0.5 | 2.0 | Cigre TB 714 (2017)12 |
| Sand (sorted) | 0.6 | 3.5 | Cigre TB 714 (2017)12 |
| Silt | 0.7 | 2.5 | Cigre TB 714 (2017)12 |
| Topsoil | 0.7 | 2.0 | NMBU measurement10 |
| Turf | 2 | 17 | SINTEF measurement10 |
| Clay | 0.25 | 17 | SINTEF measurement10 |
| Mass | Thermal Resistivity [mK/W] | Source |
|---|---|---|
| Bentonite | 0.4- 0.6 | SINTEF measurement10 |
| Tarmac | 0.5-1.0 | SINTEF measurement10 |
| Concrete for duct banks | 1.0 | IEC 60287-2-1:20239 |
| Concrete for duct banks | 0.613 | SINTEF measurement13 |
[10] SINTEF measurment is based on the report: H. Strand, “Stedlige Masser” 01.04.2021
[11] NMBU measurement is based on values recived by prof. Trond Børresen at NMBU (Norwegian University of Life Sciences)
[12] “Long term performance of soil and backfill systems” Cigre TB 714 (2017)
[13]
SINTEF measurment is based on the report: E. Eberg, S. Hellesø and R. Marskar “Termiske egenskaper for materialer for kabelforlegning” 29.06.2018
The measurement of thermal resistance in concrete typically used for cable installations in Norway yields a value of 0.6 mK/W. This aligns well with models from the literature and the value recommended by SINTEF Byggforsk for use in thermal calculations in construction.
IEC 60287
IEC 60287 has a more general approach to masses based on moisture content presented in the table below:
| Thermal resistivity [mK/W] | Mass description | Weather conditions |
|---|---|---|
| 0.7 | Very moist | Persistently moist |
| 1.0 | Moist | Regular rain |
| 2.0 | Dry | Rare rain |
| 3.0 | Very dry | Little to zero rain |
Metals:
| Thermal resistivity [mK/W] | Electrical resistivity at 20°C [μΩ*m] | Temperature coefficient [1/K] | Relative permability | |
|---|---|---|---|---|
| Steel | 0.019 3 4 | 0.138 1 2 3 4 9 | 0.0040 2 9 | 250 1 5 9 |
| Stainless steel | 0.69 8 | 0.7 6 7 8 | 0.00094 | 1 6 7 8 |
| Magnetic stainless steel | 0.69 8 | 0.7 6 7 8 | 0.00094 | 1000 6 7 8 |
References for Metals
[1] L. Meyerhoff, “A-C Resistance of Pipe-Cable Systems with Segmental Conductors,” AIEE. Trans., vol. 71, no. III, pp. 393-414, 1952.
[2] Y. Sun, D. Niu and J. Sun, “Temperature and carbon content dependence of electrical resistivity of carbon steel,” in 2009 4th IEEE Conference on Industrial Electronics and Applications, Xi’an, China, 25-27 May 2009.
[3] American Society for Metals, Metals Handbook, Ninth Edition, Volume 1, Properties and Selection: Iron and Steels, Beijing, China: China Machine Press, 1988.
[4] S. Yafei, N. Dongjie and S. Jing, “On-Line Nondestructive Evaluation of Carbon Content of Steel Using Surface Temperature during Induction Heating,” in 2009 IEEE International Conference on Mechatronics and Automation, Changchun, China, August 9 - 12, 2009.
[5] N. Bowler, “FREQUENCY-DEPENDENCE OF RELATIVE PERMEABILITY IN STEEL,” in QUANTITATIVE NONDESTRUCTIVE EVALUATION, Brunswick, Maine (USA), 31 July-5 August 2005.
[6] D. W. Dietrich, Magnetically Soft Materials, ASM Handbook, vol. 2, Properties and Selection: Nonferrous Alloys and Special-Purpose Materials, Materials Park: ASM, 1990.
[7] P. Oxley, J. Goodell and R. Molt, “Magnetic properties of stainless steels at room and cryogenic temperatures,” Journal of Magnetism and Magnetic Materials , vol. 321 , p. 2107–2114, 2009.
[8] S. Prasan and K. Erhard, Powder metallurgy stainless steels : processing, microstructures, and properties, Materials Park, Ohio: ASM International, 2007.
[9] IEC 60287
Cables in Water Filled Pipes
ρ = (2 * π * U)/(1+ 0.1 * De * ((V+(Y * θ) * ln(Dd/De)))
ρ = thermal resistivity applied to the pipe filling.
θ = the average temperature of water.
Dd = inner diameter of the pipe
De = diameter of the cable or an equivalent diameter of the group of the group of cable calculated according to IEC.
U = 0.1 (for water)
V = 0.03 (for water)
Y = 0.001 (for water)
| Source | |
|---|---|
| U = 0.1 (for water) | IEC 60287-2-1 |
| V = 0.03 (for water) | IEC 60287-2-1 |
| Y = 0.001 (for water) | IEC 60287-2-1 |
Empty water filled pipes
For empty water filled pipes and water filled pipes without a heat source, a fixed thermal resistivity of 1.6 mK/W is applied.
”The Engineering Handbook” and “The Engineering ToolBox” sets the thermal conductivity for water at 0.609 W/mK, at 26.8°C. This is recalculated to approximately 1.6 mK/W for the temperature expectet to occur in a trench.