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Skin and proximity effect coefficient a PAC/GIL conductor

The equation for $z_c$ < 5 is identical in CIGRE TB 2018 (2003), Elektra 100 (1985), and Elektra 125 (1989).

The equation for $z_c$ > 30 is acc. Elektra 125 (1989) whereas in CIGRE TB 2018 (2003) and Elektra 100 (1985) the factor 1 is falsely outside the square-root.

Coefficients of the polynomial interpolation are taken from Table II of Elektra 125 (1989). The values are identical in CIGRE TB 218 (2003).

Symbol
$a_{c}$
Formulas
$\frac{7{z_{c}}^2}{315+3{z_{c}}^2}$$z_{c}<5$
$\sqrt{\frac{z_{c}}{2}}-1$$z_{c}>30$
$0.19701-1.56295{\cdot}{10}^{-1} z_{c}+7.3796{\cdot}{10}^{-2} {z_{c}}^2-9.02854{\cdot}{10}^{-3} {z_{c}}^3+6.27032{\cdot}{10}^{-4} {z_{c}}^4-2.69028{\cdot}{10}^{-5} {z_{c}}^5+7.0674{\cdot}{10}^{-7} {z_{c}}^6-1.04301{\cdot}{10}^{-8} {z_{c}}^7+6.62315{\cdot}{10}^{-11} {z_{c}}^8$otherwise
Related
$e$
Constant $e$ [m/s$^2$]
$z_{c}$
Factor z to calculate skin effect coefficients for conductor
Used in
$y_{c}$
Skin and proximity effect factor y PAC/GIL conductor