NonMarkovian estimation of the reliability costs of power distribution systems

Unbundling and liberalization of the electric sector has led in many countries, including Portugal, to the settlement definition of quality standards for the power distribution systems that give rise to penalties when those standards are not met. Also, penalties and rewards related to global reliability indices exist in some countries. Distribution companies must take this into account when planning there systems because the minimization of the net reliability cost is a main criteria when making investment decisions performing reliability studies to support investment decisions, and penalties (or rewards) become direct reliability costs (or benefits), regardless of any other consideration concerning the impact of the frequency and duration of the interruptions. Most of the time, standards are defined in terms of the sum of the interruption durations during a year. In this paper, the details of this discussion are addressed, in the framework of the investment decision-making process. A formal model for the problem is proposed, along with methodologies able to tackle it. The inadequacy of a Markovian approach is discussed and illustrated, showing how bad investment decisions can be made due to incorrect evaluation of the reliability costs. The discussion will be illustrated with small numerical examples