## 1 Introduction  
### 1.1 Impact of Power Line Sectionalizing on Power Supply Reliability  
Sectionalizing power transmission lines (PTL) is mainly used to increase power supply (PS) reliability for consumers in power transmission lines of medium voltage (MV) level (6-35 kV). A fairly large number of devices usually called sectionalizing units (SU) and reclosers have been developed for sectionalizing electrical networks of this voltage class by such companies as Siemens, ABB, S&C Electric Co, etc. [1; 2; 3; 4]. In Russia, the most popular reclosers are produced by Tavrida Electric company group, LLC \"Elektroshchit-Samara\" [5; 6]. According to statistics given in [7], over 70% of faults in overhead distribution networks are temporary and can be cleared satisfactorily by the reclosing process. By contrast, permanent faults, despite their low frequency, have a long lifespan as compared to transient ones. The area affected by permanent faults can also be decreased using sectionalizing units, hence increasing PS reliability. Sectionalizing units divide the entire network into pieces and ensure the isolation of damaged PTL sections. As a result, a vast chunk of the network, except the faulted segments, can be spared from PS outage. According to [8; 9; 10], the experience of using protective devices such as SUs and reclosers shows that PS reliability for consumers increases by 15-30% depending on the type of used device, the length of sectionalized PTL, the allocation of load over the PTL sections, and other factors. For example, the paper [8] proved that the right choice of recloser placement gives improvements in SAIDI by 15-20% and in CENS (costs of energy not supplied) by up to 30%. The installation of reclosers in the electrical networks of ELMU Network Ltd. and EMASZ Network Ltd. allowed decreasing the PS reliability indicator SAIDI (system average interruption duration index) by 25-29% [9]. The mounting of feeder automation and remotely controlled disconnectors along with the MV PTLs' renovation at Swedish Fortum Distribution Networks showed a reduction in SAIDI indicator by a significant number--42% [10]. In considering low voltage (LV) networks, that is, up to 1 kV, sectionalizing means are promising both for improving PS reliability for consumers and for enhancing PTL protection against remote short circuits (SC) and the differentiation of electricity metering. The fact is that the lines of this level are of large length and the sensitivity of the protective devices installed at the beginning of lines to single-phase SC currents is not provided. In addition, in PTLs up to 1 kV (usually 0.4 kV lines), there are increased electricity losses often associated with unaccounted and non-contractual consumption, that is, with the theft of electricity [11]. These losses are often referred to as commercial losses, and the majority of developing countries suffer from them. So, the losses in such counties as India, South Africa, Brazil, China, and Russia account for approximately 10-40%, whereas in the UK, the USA, and Australia, it equals roughly 0.2-1% [12]. Differentiation of electricity metering consisting of the installation of additional metering devices at different line sections (e.g., at reclosers and SUs) allows identifying line sections with increased losses [13]. Although the experience of usage of distribution network protection means shows a significant increase in PS reliability, PTL sectionalizing and redundancy means in rural areas including both LV and MV electrical networks are not widespread due to moderate consumer loads as well as a radial design of used PTLs, their excessive length, and the lack of alternate backup supplies from other adjacent feeders [14]. This is despite the fact that the permanent fault frequency for rural networks is much more than for urban ones; for example, this indicator at the premises of Finish rural networks exceeds urban ones by approximately two times (according to the data presented in paper [15]).