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The inductance, L , per core of a 3-core cable or of three single-core cables comprises two parts namely the self-inductance 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 single-core cables (mm)
d = conductor diameter or for shaped designs the diameter of an equivalent circular
conductor (mm)
For 2-core, 3-core and 4-core cables, the inductance obtained from the formula should be multiplied by 1.02 if the conductors are circular or sector-shaped, and by 0.97 for 3-core 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
|
