Loss factor of armour by circulating currents

The loss factor of armour caused by circulating currents is calculated acc. to IEC 60287-1-1, clause 2.4.2.4, used for three-core cables with steel tape armour or reinforcement.

We likewise use this factor to calculate the loss factor of armour for SL-type cables.

Symbol
$\lambda_{21}$
Formulae
$\frac{{10}^{-7}{s_c}^2}{R_c d_{ar} \delta_{ar}} \left(\frac{1}{1+\frac{d_{ar}}{\mu_s \delta_{ar}}} \frac{f}{50}\right)^2$three-core cables with steel tape armour or reinforcement
$\frac{\frac{1.23R_{ar}}{R_c} \left(\frac{2s_c}{\sqrt{3} d_{ar}}\right)^2}{\left(\frac{2.77R_{ar}{\cdot}{10}^6}{\omega}\right)^2+1}$SL-type three-core cables with steel wire armour, with round conductors
$\frac{\frac{0.358R_{ar}}{R_c} \left(\frac{d_c}{d_{ar}}\right)^2}{\left(\frac{2.77R_{ar}{\cdot}{10}^6}{\omega}\right)^2+1}$SL-type three-core cables with steel wire armour, sector-shaped conductors