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Loss factor of magnetic steel ducts

The loss in duct made of ferromagnetic steel is calculated in the same fashion as the loss in steel pipes of pipe-type cables.

Symbol
$\lambda_4$
Formulae
${10}^{-5}\frac{0.0115s_c-0.001485Di_d}{R_c}$three single-core cables in trefoil in magnetic steel pipe
${10}^{-5}\frac{0.00438s_c+0.00226Di_d}{R_c}$three single-core cables in cradled formation in magnetic steel pipe
$\lambda_4 \left(\frac{f}{60}\right)^2 \sqrt{\frac{60}{f}}$other frequencies than 60 Hz
$0$steel pipe is non-magnetic or a pipe-type cable with flat-wire armour over all three cores after they are laid up is used
Related
$Di_d$
Inner diameter of duct [mm]
$f$
System frequency [Hz]
$\lambda_3$
Loss factor of steel pipes for pipe-type cables
$R_c$
Electrical resistance of conductor [$\Omega$/m]
$s_c$
Separation of conductors in a system [mm]
Used in
$I_c$
Conductor current [A]
$q_4$
Ratio of losses affecting environment
$T_{eq}$
Equivalent thermal resistance [K.m/W]
$W_{duct}$
Losses in duct [W/m]
$W_h$
Heat generated by external object [W/m]
$W_I$
Ohmic losses per phase [W/m]