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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:

Symbol
$T_{4t}$
Unit
K.m/W
Formulas
$N_{sys} N_{c} \left(T_{s}+\left(T_{t}+T_{e}\right) \left(1-\frac{T_{t}+T_{e}}{T_{a}+T_{t}+T_{e}} e^{\frac{-L_{T}}{L_{0}}}\right)\right)$
Related
$L_{0}$
Reference length of the tunnel [m]
$L_{T}$
Length tunnel [m]
$N_{c}$
Number of sources in system
$N_{sys}$
Number of parallel systems in the same confinement
$T_{a}$
Star thermal resistance air [K.m/W]
$T_{e}$
External thermal resistance of tunnel [K.m/W]
$T_{s}$
Star thermal resistance object [K.m/W]
$T_{t}$
Star thermal resistance tunnel [K.m/W]
Used in
$\Delta \theta_{c}$
Temperature rise conductor [K]
$\Delta \theta_{d}$
Temperature rise dielectric losses [K]
$I_{c}$
Conductor current [A]
Image

IEC standard 60287-2-3 Ed. 1.0 (2017) Figure B.1