Mean distance between the phases, pipe-type cables

Definition according to Cigré guide 531 chapter 4.2.4.3

Symbol
$S_{sp}$
Unit
$\Omega$/m
Formulae
$D_{core}$trefoil
$1.26\left(1-\left(\frac{D_{core}}{Di_{sp}-D_{core}}\right)^2\right)^{\frac{1}{6}}$cradled
Related
Used in
$X_1$
$X_d$