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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
$\frac{{10}^{-7}{s_c}^2 \left(\frac{1}{1+\frac{d_{ar}}{\mu_s \delta_{ar}}}\right)^2}{R_c d_{ar} \delta_{ar}} \left(\frac{f}{50}\right)^2$Three-core cables, steel wire armour or reinforcement
$1.23\frac{R_{ar}}{R_c} \left(\frac{2c_c}{d_{ar}}\right)^2 \frac{1}{\left(\frac{2.77R_{ar}{\cdot}{10}^6}{\omega}\right)^2+1}$Three-core cables, round conductors, SL-type, steel wire armour
$0.358\frac{R_{ar}}{R_c} \left(\frac{2r_1}{d_{ar}}\right)^2 \frac{1}{\left(\frac{2.77R_{ar}{\cdot}{10}^6}{\omega}\right)^2+1}$Three-core cables, sector-shaped conductors, SL-type, steel wire armour
Related
$c_c$
Distance between the axis of a conductor and the cable center [mm]
$d_{ar}$
Mean diameter of armour [mm]
$\delta_{ar}$
Equivalent thickness of armour [mm]
$f$
System frequency [Hz]
$\mu_s$
Relative permeability
$\omega$
Angular frequency [rad/s]
$r_1$
Radius of the circle circumscribing the shaped conductors [mm]
$R_{ar}$
Electrical resistance of armour [$\Omega$/m]
$R_c$
Electrical resistance of conductor [$\Omega$/m]
$s_c$
Separation of conductors in a system [mm]
Used in
$I_{ar}$
Induced circulating current armour [A]
$\lambda_2$
Loss factor of armour