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The inductance, L , per core of a 3core cable or of three singlecore cables comprises two parts namely the selfinductance of the conductor and the mutual inductance with other cores.
The formula for calculating the Inductance of a cable is given by:
$L = K + 0.2Log_e{\frac{2S}{d}}$ (Hm/Km)
Where:
L = Inductance of cable in (Hm/Km)
L = Inductance of cable in (Hm/Km)
K = a constant relating to the conductor formation (see table below)
S = axial spacing between conductors within the cable (mm) or axial spacing between
Conductors of a trefoil group of single core cables (mm) or
= 1.26 x phase spacing for a flat formation of three singlecore cables (mm)
d = conductor diameter or for shaped designs the diameter of an equivalent circular
conductor (mm)
For 2core, 3core and 4core cables, the inductance obtained from the formula should be multiplied by 1.02 if the conductors are circular or sectorshaped, and by 0.97 for 3core oval conductors.
Typical Values for K for Different Stranded Conductors (at 50Hz)
Number of Wires in Conductor

K

3

0.0778

9

0.0642

7

0.0554

37

0.0528

61 and Over

0.0514

1 (Solid)

0.0500

Hollow core conductor, 12mm duct

0.0383
