The supply system of distribution transformer station Beričevo has to be reliable, because it is an important facility in Slovenia. ELES Ltd. has had problems in the past with the failure of one of the transformers at the tertiary winding, hence they have decided for renovation and built a 110/20 kV transformation into the supply system. They chose among three options. The first option was to reconstruct the transformer in the event of failure and to insulate and protect the tertiary winding’s leads. This option is not economical and undermines the reliability of electric power transmission. The second option was to power the supply system through a distribution network. Because of the unreliability of such power, the ELES Ltd. decided on the third option – the construction of a new supply system. This option is not the most financially favourable, but they‘ve assessed the reliability and independence of powering the supply system from other power sources that are not owned or controlled by ELES Ltd.