CHAROONG THAI WIRE & CABLE PUBLIC COMPANY LIMITED
INDUCTANCE, REACTANCE, IMPEDANCE
INDUCTANCE
Inductance (L) : The property of a circuit or circuit element that opposes a change in current flow. Inductance thus causes current changes to lag
behind voltage changes. Inductance is measured in henries (H). Inductance per core of a 3 core cable or of three single core cables comprises
two parts, self inductance of the conductor and the mutual inductance with the other cores.
For energy cables
L = K + 0.2 *loge( 2S / d ) ( mH/km)
where
K = Constant relating to the conductor formulation
Number of wires in conductor
K (50Hz)
1
0.0500
3
0.0778
7
0.0642
19
0.0554
37
0.0528
61 and over
0.0514
S = Axial spacing between conductors within the cable, or
Axial spacing between conductors in a trefoil group, or
1.26 x phase spacing for a flat formation of 3 single core cables
0.5 x pcd of neutral screen for single core neutral screen cables (mm).
d = conductor diameter (or for shaped designs, the diameter of an equivalent circular conductor (mm).
REACTANCE (Inductive Reactance)
X = 2 * * f*L (
/km)
where
f = Frequency (Hz)
L = Inductance (mH/km)
IMPEDANCE
The total opposition that a circuit offers to the flow of alternating current
Z =
Note : Final AC volt drop Vac =
64 Medium & High Voltage Power Cable
( Resistance2 + Reactance2) ( km)
(Voltage2resistance + Voltage2reactance )