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Effective length per unit lay length of twisted conductors

The fact that triplex or three core cables are twisted together leads to the possible need of a correction factor to take into account the longer length of the cores. This correction factor is the lay length factor as given in Cigre TB 880 Guidance Point 20.

A typical lay length factor is 1.01.

Symbol
$F_{lay,3c}$

Default
1.01

Formulae
$\sqrt{1+\left(\frac{\pi D_{lay,3c}}{L_{lay,3c}}\right)^2}$
Related
$D_{lay,3c}$
Diameter of mechanical neutral line [mm]
$L_{lay,3c}$
Length of lay of twisted conductors [mm]
$\pi$
Archimedes' constant $\pi$
Used in
$C_b$
Capacitance of insulation [F/m]
$R_{c20}$
DC resistance of conductor at 20°C [$\Omega$/m]
$T_1$
Thermal resistance between one conductor and sheath [K.m/W]