Conductor to surface attainment factor

This is the attainment factor for the temperature rise of the conductor above the outside surface of the cable according to the IEC 60853-2 standard. This factor takes the thermal capacitance of the cable into account and approaches a value of 1.0 if the transient time periods are sufficiently long compared to the thermal time constant of the cable.

The applied formula is equivalent to the folloeing formula: $\Delta\theta_{c_t}/(n_{c}W_{c}(T_A+T_B))$

$\frac{T_{a0} \left(1 - e^{- a_{0} \tau}\right) + T_{b0} \left(1 - e^{- b_{0} \tau}\right)}{T_{A} + T_{B}}$
Used in
$\Delta \theta_{t}$