Effective transient thermal resistance in the earth for yearly load:

For deeply buried cables and for tunnels, the yearly load variations play a significant role because of the very long constants at great depths.

For more information, refer to the transient thermal resistance $T_4et$..

Symbol
$T_{\mathrm{4y}}$
Unit
K.m/W
Formulae
$\frac{\rho_{\mathrm{4}}}{2 \pi} \ln{\left (\frac{D_{\mathrm{x_{\mathrm{y}}}}}{Do_{\mathrm{d}}} \right )}$
Related
$D_{\mathrm{x_{\mathrm{y}}}}$
$Do_{\mathrm{d}}$
$\pi$
$\rho_{\mathrm{4}}$
$T_{\mathrm{4et}}$
Used in
$T_{\mathrm{4\mu}}$