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Thermal resistance ambient

This is the effective thermal resistance in the earth, typically just named $T_4$.

Symbol
$T_{4\mu}$
Unit
K.m/W
Formulas
$T_{4ss}$without cyclic load variation (continuous load)
$T_{4ss} \left(\mu+\frac{\left(1-\mu\right) T_{4d}}{T_{4ss}}\right)$with cyclic load variation (daily)
$T_{4ss} \left(\mu+\frac{\left(1-\mu\right) T_{4d}}{T_{4ss}}\right) \left(\mu_w+\frac{\left(1-\mu_w\right) T_{4w}}{T_{4ss}}\right)$with cyclic load variation (daily, weekly)
$T_{4ss} \left(\mu+\frac{\left(1-\mu\right) T_{4d}}{T_{4ss}}\right) \left(\mu_w+\frac{\left(1-\mu_w\right) T_{4w}}{T_{4ss}}\right) \left(\mu_y+\frac{\left(1-\mu_y\right) T_{4y}}{T_{4ss}}\right)$with cyclic load variation (daily, weekly, yearly )
$F_{\alpha} T_{4\mu}$buried inclined cable / duct
Related
$F_{\alpha}$
Inclination derating factor [p.u.]
$\mu$
Loss factor daily load variation [p.u.]
$\mu_w$
Loss factor weekly load variation [p.u.]
$\mu_y$
Loss factor yearly load variation [p.u.]
$T_{4d}$
Thermal resistance daily load cycle [K.m/W]
$T_{4ss}$
Thermal resistance steady-state [K.m/W]
$T_{4w}$
Thermal resistance weekly load cycle [K.m/W]
$T_{4y}$
Thermal resistance yearly load cycle [K.m/W]
Used in
$\Delta \theta_c$
Temperature rise conductor [K]
$\Delta \theta_{duct}$
Temperature rise duct (magnetic) [K]
$I_c$
Conductor current [A]
$T_{eq}$
Thermal resistance, equivalent [K.m/W]
$T_r$
Thermal resistance, total [K.m/W]
$\theta_{de}$
Temperature duct outer surface [°C]
$\theta_e$
External temperature object [°C]