Modern societies rely heavily on the operations of Electrical Power Infrastructure (EPI). Such infrastructure is characterized by direct or indirect interdependencies among its systems. In other words, EPI systems are interrelated. A disturbance in one part of those systems may lead to disturbances in the whole network. Therefore, in order to design a systemic plan for EPI protection, all system levels must be classified in terms of importance. This paper discusses the interdependencies of EPI through a real-life case-study to reveal the most critical parts of the network. By applying Interpretive Structural Modelling (ISM) method, the paper examines the physical interactions of thirty electrical substations in EPI according to their influence. Furthermore, the paper identifies the driving substations that can affect other substations. The proposed model uses MICMAC to analyse the driving power and dependence of that substation. Finally, based on the results of the study, the paper concludes that the suggested approach can shape the foundation of new analysis of EPI network for better decision-making