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Thermal resistance to ambient

Symbol
$T_{4\mu}$
Unit
K.m/W
Formulae
$T_{4ss}$without cyclic load variation (continuous load)
$T_{4ss} \left(\mu+\frac{\left(1-\mu\right) T_{4d}}{T_{4ss}}\right)$with cyclic load variation
$T_{4ss} \left(\mu+\frac{\left(1-\mu\right) T_{4d}}{T_{4ss}}\right) \left(\mu_w+\frac{\left(1-\mu_w\right) T_{4w}}{T_{4ss}}\right)$with daily and weekly cyclic load variations
$T_{4ss} \left(\mu+\frac{\left(1-\mu\right) T_{4d}}{T_{4ss}}\right) \left(\mu_w+\frac{\left(1-\mu_w\right) T_{4w}}{T_{4ss}}\right) \left(\mu_y+\frac{\left(1-\mu_y\right) T_{4y}}{T_{4ss}}\right)$with daily, weekly and yearly cyclic load variations
$F_{\alpha} T_{4\mu}$buried inclined cables and ducts
Related
$F_{\alpha}$
Inclination derating factor [p.u.]
$\mu$
Loss factor [p.u.]
$\mu_w$
Loss factor for weekly load variation [p.u.]
$\mu_y$
Loss factor for yearly load variation [p.u.]
$T_{4d}$
Thermal resistance for daily load cycle [K.m/W]
$T_{4ss}$
Steady-state thermal resistance [K.m/W]
$T_{4w}$
Thermal resistance for weekly load cycle [K.m/W]
$T_{4y}$
Thermal resistance for yearly load cycle [K.m/W]
Used in
$\Delta \theta_c$
Temperature rise of conductor [K]
$\Delta \theta_{duct}$
Temperature rise by losses in ferromagnetic duct [K]
$I_c$
Conductor current [A]
$T_{eq}$
Equivalent thermal resistance [K.m/W]
$T_r$
Total thermal resistance [K.m/W]
$\theta_{de}$
Temperature of duct outer wall [°C]
$\theta_e$
External temperature of the object [°C]