## 1 Introduction  
The deregulation of the electricity market and the introduction by national authorities of reward/penalty mechanisms are driving distribution network operators (DNOs) to improve the reliability performance of distribution systems [1]. The DNOs can employ different strategies to improve the reliability performance of the distribution networks: executing network maintenance actions to prevent fault events [2]; reallocating or installing additional switches along the distribution network [3]; introducing telecontrol and automation systems [4]; adopting new network management paradigms, such as operating some portions of the network in island mode when a fault occurs [5], _i.e._, disconnecting them from the main network and supplying by local generation; and so on. Environmental and long-term primary energy resources provision concerns are driving towards an increasingly diffusion of renewable energy technologies [6]. In Europe the 20-20-20 2020 climate & energy package (aiming to meet 20% of energy needs by means of renewable sources and reduce both energy consumption and pollutant emissions by 20% by 2020 [7]) has led many countries to introduce new policies that provide incentives for using renewable energy sources and maximizing energy efficiency. Therefore, considering that the distribution system has been planned and managed by means of procedures dating back to the 1960s, DNOs have to face a new challenging scenario. The Smart Grid (SG) paradigm [8] is the key to addressing these issues; indeed, it is expected that SG will exploit communication and automation systems to minimize the impact of renewable-based Distributed Generators (DGs) on the distribution network. On the other hand, SG can convert DGs into a resource by managing them [9]. In fact, from an SG perspective the possibility of meeting the load of intentional islands by means of local generation combined with the introduction of telecontrolled switches is desirable from a reliability point of view [4]. The use of telecontrolled sectionalizers enables the DNO to quickly restore the portion of the network not affected by the fault, thereby improving the average annual outage duration per customer. In recent years, \"Global System for Mobile communications\" (GSM) technology has been adopted and telecontrolled sectionalizers have been installed in order to meet the target imposed by the authorities [10]. On the other hand, reducing the average annual outage rate per customer requires installing telecontrolled circuit breakers (CBs). In this paper, delayed operation of the CBs is considered to perform logic selectivity. In other words, when a fault occurs, a centralized control system receives information about the fault current directions from the CBs that detected the fault. These CBs do not open instantaneously (since a delayed tripping time is adopted) but they send such information to the control system. After that, according to the logic selectivity, the CBs closest to the fault receive an opening authorization while the others receive a command that forces them to remain closed in order to leave the smallest portion (faulted zone) of the network unsupplied (a CB is considered the \"closest\" to the fault if there is not any CB between itself and the fault). For safety reasons, a CB has to be opened when it detects the fault but does not receive any communication within its delayed operation time. More specifically, the network protected by the CB could be damaged due to a fault current persisting beyond the physically admissible time; hence the delay time has to be properly chosen and the CB is automatically opened by local control when it does not receive a command that forces it to remain closed. Therefore, smart communications subsystems (SCSs) that enable to open the closest CBs while keeping the others closed with a reasonable time delay are investigated in the paper.