Contents I. Introduction
The decision making in the planning stage of electric transmission networks, in particularly, and power system, in general, represents a key activity that involves the identification of optimal solutions, economically and technically feasible. Also, in any important investment project, the decision maker must consider certainly in the technical and economic calculations that both expenditure and income is spread values over time. The process is represented by a successive series of decisions, and these are choices among several available alternatives in order to achieve one or more objective. The scientific substantiation of the decisions, regardless of the situation involved, can be considered as a systematic process, consisting of several phases: defining the problem, highlight the available variants, evaluating the possible variants in terms of consequences, and substantiating and selecting the optimal variant. The considered variants differ from the economic point of view by the value of initial investments and the discounted values of costs. The comparison of variants can be only achieved by discounting all present and future expenses and benefits at the same time. Another aspect to be considered in economic calculations is represented by discount rate which affect all amounts engaged in the investment project. Undoubtedly, as the analysis of all investment projects are carried out on longer study periods (from 5 till 15 years), it should take into account the nature of the information available [1]–[3]. Few input data are known in a deterministic analysis, most information is uncertain (e.g., growth of demands from supply areas, the price of energy resources, electricity tariff, and the discount rate during the period of study etc.) [4], [5]. If this uncertainty is not modelled, then determination of the optimal solution can be affected. Thus, this uncertainty must be present in decision-making. The approach that could model the uncertainty in decision analysis is based on the fuzzy set theory [6], [7]. Usually, to model the uncertainty in economic calculations from power engineering is used the probability theory.
