The loss in steel pipes is given in the IEC by two empirical formulae, one for cables where the cores are bound in close trefoil formation and the other where the cores are placed in a more open configuration (cradled) on the bottom of the pipe. We calculate the ratio of the pipe inside diameter to cable outside diameter and if this ratio is larger than 3, cradled configuration is assumed otherwise triangular.
To be noted:
$\frac{1}{R} \left(- 1.485 \cdot 10^{-8} Di_{\mathrm{d}} + 1.15 \cdot 10^{-7} s_{\mathrm{c}}\right)$ | three single-core cables in trefoil in magnetic steel pipe |
$\frac{1}{R} \left(2.26 \cdot 10^{-8} Di_{\mathrm{d}} + 4.38 \cdot 10^{-8} s_{\mathrm{c}}\right)$ | three single-core cables in cradled formation in magnetic steel pipe |
$\frac{\sqrt{15} f^{2}}{1800} \sqrt{\frac{1}{f}}$ | multiplication factor for other frequencies than 60 Hz |
$0$ | steel pipe is non-magnetic |