# Equivalent thermal resistance for tunnel

A delta-star transformation is used to derive the following parameters used to calculate the equivalent thermal resistance of the surrounding soil of a tunnel:

• $T_s$ is the equivalent star thermal resistance of cable
• $T_t$ is equivalent star thermal resistance of tunnel wall
• $T_a$ is the equivalent star thermal resistance of air.

Symbol
$T_{4t}$
Unit
K.m/W
Formulae
$N_{sys} N_c \left(T_s+\left(T_t+T_e\right) \left(1-\frac{T_t+T_e}{T_a+T_t+T_e} e^{\frac{-L_T}{L_0}}\right)\right)$
Related
$L_0$
$L_T$
$T_a$
$T_e$
$T_s$
$T_t$
Used in
$\Delta \theta_c$
$\Delta \theta_d$
$I_c$
Image
IEC standard 60287-2-3 Ed. 1.0 (2017) Figure B.1