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Inductance & Reactance

Inductance of a cable consist of two parts:

  1. the self-inductance of the conductor
  2. the mutual inductance between conductors

BICC Electrical Cables Handbook

The BICC Electric Cables Handbook, give the formuale for inductance as:

L=( K+0.2ln 2S d )× 10 6

where:
L - cable inductance, H.m-1
K - conductor formation constant
S - axial spacing between conductors within a cable, mm
- axial spacing between condcutors in trefoil, mm
- 1.26 x phase spacing of flat formation conductors, mm
d - condcutor diamters, mm

For 2, 3 or 4-core circular or sector-shaped cables, multiply the above by 1.02 to obtain the inductance.  Multiply by 0.97 for 3-core oval conductors.

Typical values of K

Number of wire in conductor  K
 1 (solid) 0.0500
3  0.0778
7  0.0642
19  0.0554
37  0.0528
 61 and over  0.0514

Reactance

The reactance of a conductor is given by:

X=2πfL

where:

X - reactance in Ω.m-1
L i indcutance in H.m-1

 

CENELEC CLC/TR 50480

Equations for inductance are given by CENELEC CLC/TR 50480 "Determination of cross-sectional area of conductors and selection of protective devices".

Three-line or line to line:

 

Line to neutral:

 

where:
x - reactance per metre of conductors, mΩ.m-1
Xc - reactance of conductor, mΩ
XcN
XcPE -
XcPEN

 

IEC 60909

See Impedance

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