## 1 Introduction
Although a lot of work has been done in the past regarding the choice of an appropriate technology for an SCS [11], the suitability of different solutions for information exchange when a fault occurs in the distribution network has rarely been investigated. The most used adequacy indices are the Loss of Load Expectation (LOLE), the Loss of Load Probability (LOLP), and the Loss of Energy Expectation (LOEE) [12]. Such indices could be adopted to evaluate the adequacy of local DGs supplying an island, but they do not account for load curtailment policies since they consider load shedding only [13]. In [5] a new adequacy index, called Probability of Adequacy (PoA), has been proposed to overcome this limitation. The main merit of the PoA assessment approach is its ability to account for the probability that a given load and a given generation level occur when a network portion intentionally passes from the connected to the island mode of operation, as well as considering load shedding and/or curtailment policies. On the other hand, this approach neglects the variations of load and generation that usually occur when the island mode is maintained for several hours, and, consequently overestimates the ability of islanding to improve distribution system reliability. This aspect is crucial especially when renewable DGs are considered, due to the fluctuating behavior of their primary (green) energy sources (wind, sun) [14]. The present work proposes an efficient computational approach that is able to overcome the limitation of the previous ones and also account for load and generation correlations, thus obtaining a very accurate measure of the reliability improvement that can be achieved thanks to islanding in distribution networks where telecontrolled CBs as well as telecontrolled and manual sectionalizers are installed. In order to calculate distribution network reliability, the analytical equations of load point outage rate and duration that account for a protection scheme based on telecontrolled switches [4] are combined with the formulation proposed for adequacy computation. Such a formulation uses a Markov chain for modeling the ratio between load and generation. Thanks to its properties of capturing both first- and second-order statistics [15], the proposed Markov chain is also able to represent the fluctuation during islanding of load and green-energy generators and accounting for correlations. It is to be noted that supplying as many customers as possible each time a change occurs in the load and/or generation level is the best strategy in terms of average outage duration but it is the worst in terms of average outage frequency, since some customers can be repeatedly left unsupplied and reconnected many times during islanding. Therefore, the proposed formulation for adequacy computation does not consider resupplying those customers previously left unsupplied during islanding. Obviously, those customers will be reconnected to the network after the fault is repaired. The rest of the paper is structured as follows. In Section 2 the background is reported for the sake of completeness. A brief overview of telecommunications technologies is presented in Section 3, with reference to their suitability for the considered protection scheme. In Section 4, the proposed model approach is described, by means of Markov chains, the behavior of loads, and distributed generators. Such models are applied in Section 5 to provide the proposed indices as a measure of the adequacy of island generation. A case study is presented in Section 6 and the conclusions in Section 7. Finally, the nomenclature is reported in the \"Abbreviations\" section.