Skin and proximity effect coefficient b for GIL enclosure

The coefficient is not used for calculation of skin effect factor for GIL enclosure as falsely written in CIGRE Guide 2018 (2003).

Symbol
$b_{encl}$
Formulae
$\frac{56}{z_{encl}^{2} + 211}$$z_{encl} < 5$
$\frac{2}{4 \sqrt{2} \sqrt{z_{encl}} - 5}$$z_{encl} > 30$
$2.509622 \cdot 10^{-10} z_{encl}^{8} - 3.3893677 \cdot 10^{-8} z_{encl}^{7} + 1.9109965 \cdot 10^{-6} z_{encl}^{6} - 5.8238557 \cdot 10^{-5} z_{encl}^{5} + 0.0010372874 z_{encl}^{4} - 0.01089373 z_{encl}^{3} + 0.06495563 z_{encl}^{2} - 0.21030734 z_{encl} + 0.5356$otherwise