duty_factor_cables: Duty Factor for all cables (incl. submarine cables).
Description
This function calculates the duty factor for under all types of
cables depending on the maximum
percentage utilisation under normal operating conditions.
The duty factor is used in the deriviation of the expected life of an asset.
See e.g. expected_life(). For more general information about
the derivation of the duty factor see section 6.6 on page 51 in CNAIM (2021)