^{a}and Marko Čepin

^{b}

^{a}nikolaveljanovski94@gmail.com

^{b}marko.cepin@fe.uni-lj.si

The reliability indices are important parameters used in the power systems primarily for the determination of the quality of the power supply and allocation of the resources for restoration, improvement and further development of the power systems. The ongoing transition in the power systems from deterministically to probabilistically based planning methods calls for probabilistic representations of the reliability indices. One of the most widely used reliability indices in the distribution power systems are System Average Interruption Frequency Index (SAIFI) and System Average Interruption Duration Index (SAIDI). Traditionally, both of them have been calculated as an average of the total interruptions and their durations per costumer, respectively, within the system. The objective of this work is to develop an extension of both methods in sense to replace the one-point average value with the most appropriate probability distribution functions. The procedures have been developed and the probability distribution functions of SAIFI and SAIDI were estimated instead of point average values. The data point of each outage or of each group of outages was evaluated against the known distributions utilizing the Kolmogorov-Smirnov test. The method and procedures were tested on a small superficial example. Then they were applied to a real regional power distribution system for some selected years of their operation. The results show relatively good fit of normal distribution function. The results show a different standard deviation for different groups of SAIDI and SAIFI.