This work consists in a detailed reliability analysis of the control, automation, and communication equipment in an IEC61850 based digital electrical substation considering four different communication architectures. Three preventive maintenance plans are defined according to Birnbaum’s importance measure in order to evaluate if a more detailed planning proves to be beneficial. The method used to perform the substation’s reliability and availability analysis consists in a Markov-Monte Carlo algorithm. Moreover, a quantitative cost analysis throughout the substation’s life cycle is conducted to conclude about the economic feasibility of each architecture, allowing more objective decisions to be taken when considering the reliability requirements for electric power systems. This paper is an extract from the academic research conducted by the first author as requirement to obtain the Master of Science Degree in Electrical and Computer Engineering at Instituto Superior Técnico, Universidade de Lisboa, under the supervision of Prof. Paulo J. Costa Branco and the co-supervision of Eng. Andrés A. Zúñiga.