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The geometric constant of the circle where the soil has dried out $D_{dry}$ is based on the book 'Kabel und Leitungen für Starkstrom' by L. Heinhold, 5th edition 1999 (in German).
| $e^{\frac{2\pi \Delta \theta_{x}}{\rho_{4} n_{ph} \left(\mu W_{I}+W_{d}\right)}}$ | 1 cable, $D_{dry} > D_{x}$ |
| $e^{\frac{\frac{2\pi \Delta \theta_{x}}{\rho_{4} n_{ph}}+\left(1-\mu\right) W_{I} \ln\left(g_{x}\right)}{W_{I}+W_{d}}}$ | 1 cable, $D_{dry} < D_{x}$ |
| $e^{\frac{2\pi \Delta \theta_{x}}{\rho_{4} N_{c} \left(\mu W_{I}+W_{d}\right)}}$ | 2 cables flat touching / 3 cables touching trefoil, $D_{dry} > D_{x}$ |
| $e^{\frac{\frac{2\pi \Delta \theta_{x}}{\rho_{4} N_{c}}+\left(1-\mu\right) W_{I} \ln\left(g_{x}\right)}{W_{I}+W_{d}}}$ | 2 cables flat touching / 3 cables touching trefoil, $D_{dry} < D_{x}$ |
| $e^{\frac{2\pi \Delta \theta_{x}}{\rho_{4} N_{c} \left(\mu W_{I}+W_{d}\right)}}$ | 2/3 cables flat spaced, $D_{dry} > D_{x} > 2s_{c}$ |
| $e^{\frac{2\pi \Delta \theta_{x}}{\rho_{4} N_{c} \left(\mu W_{I}+W_{d}\right)}}$ | 2/3 cables flat spaced, $D_{dry} > 2s_{c} > D_{x}$ |
| $e^{\frac{\frac{2\pi \Delta \theta_{x}}{\rho_{4} N_{c}}+\left(1-\mu\right) W_{I} \ln\left(g_{x}\right)}{W_{I}+W_{d}}}$ | 2/3 cables flat spaced, $D_{x} > D_{dry} > 2s_{c}$ |
| $e^{\frac{\frac{2\pi \Delta \theta_{x}}{\rho_{4}}+N_{c} \left(1-\mu\right) W_{I} \ln\left(g_{x}\right)-2\left(W_{I}+W_{d}\right) \ln\left(g_{a}\right)}{W_{I}+W_{d}}}$ | 2/3 cables flat spaced, $D_{x} > 2s_{c} > D_{dry}$ |
| $e^{\frac{\frac{2\pi \Delta \theta_{x}}{\rho_{4}}+2\left(\mu W_{I}+W_{d}\right) \ln\left(g_{a}\right)}{\mu W_{I}+W_{d}}}$ | 2/3 cables flat spaced, $2s_{c} > D_{dry} > D_{x}$ |
| $e^{\frac{\frac{2\pi \Delta \theta_{x}}{\rho_{4}}+\left(1-\mu\right) W_{I} \ln\left(g_{x}\right)-2\left(\mu W_{I}+W_{d}\right) \ln\left(g_{a}\right)}{W_{I}+W_{d}}}$ | 2/3 cables flat spaced, $2s_{c} > D_{x} > D_{dry}$ |
Kabel und Leitungen für Starkstrom, Kap. 18.4.3 Diameter of the dry area, L. Heinhold (Siemens/Pirelli 1999)