# Transient temperature rise of outer surface

The transient response of the cable environment is calculated by an exponential integral formula which is the direct transient equivalent of the steady-state procedure adopted in IEC 60287, for groups of separate cables.

Note: The parameters $D_o$ and $L_{cm}$ are in meters.

Symbol
$\Delta \theta_{e,t}$
Unit
K
Formulae
$\frac{\rho_4 W_I}{4\pi} \left(-\operatorname{expi}\left(\frac{-{D_o}^2}{16\tau \delta_{soil}}\right)--\operatorname{expi}\left(\frac{-{L_{cm}}^2}{\tau \delta_{soil}}\right)\right)$
Related
$D_o$
$\delta_{soil}$
$L_{cm}$
$\tau$
$W_I$
Used in
$\Delta \theta_t$