This is the coefficent $b_0$ used for calculating cable partial transient temperature rise acc. to IEC 60853-2.

Symbol
$b_{\mathrm{0}}$
Unit
1/s
Formulae
$\frac{1}{N_{\mathrm{0}}} \left(M_{\mathrm{0}} - \sqrt{M_{\mathrm{0}}^{2} - N_{\mathrm{0}}}\right)$
Used in
$\alpha_{\mathrm{t}}$
$\Delta \theta_{\mathrm{c_{\mathrm{t}}}}$
$\Delta \theta_{\mathrm{d_{\mathrm{t}}}}$
$T_{\mathrm{a0}}$