Impedance of shield inner surface

Definition according to Cigré guide 531 chapter 4.2.1

Symbol
$\mathscr{z}_3$
Unit
$\Omega$/m
Formulae
$\mathscr{z}_{3,sc}$screen
$\mathscr{z}_{3,sh}$sheath
$\mathscr{z}_{3,sc}-\frac{{\mathscr{z}_{4,sc}}^2}{\mathscr{z}_{5,sc}+\mathscr{z}_6+\mathscr{z}_{3,sh}}$composite screen and sheath
Related
$\mathscr{z}_{3,sc}$
$\mathscr{z}_{3,sh}$
$\mathscr{z}_{4,sc}$
$\mathscr{z}_{5,sc}$
Used in
$\mathscr{z}_{cc}$
$\mathscr{z}_{int}$