## 1 Introduction
### Article Relevance, Contribution and Organization  
In the works discussed above, a large number of approaches are used to determine the quantity and location of sectionalizing units for medium voltage lines. For networks with voltage below 1 kV, due to the small experience of using SU, there are almost no such developments. This is based mainly on the fact that SU installation in LV networks is considered economically irrational, since the calculations are carried out using the existing methods of economic justification for MV networks. However, LV networks often exceed the permissible length established by the regulatory documents' requirements, for example, as indicated in [36], the average length of 0.4 kV rural PTLs in Russia is 0.9-1.2 km, and in some cases, it reaches 3-4 km. Thus, a situation arises when the current value of single-phase SC to ground at the end of PTL is less than the value of the load current of the whole line. Such short circuits often occur when a wire breaks and falls to the ground. As a result,the protective switching device at the beginning of PTL does not feel such short-circuits and does not trigger off when they appear. In such cases, SU installation in electrical networks should be obligatory to ensure electrical safety. In turn, this situation does not manifest itself in a similar way for MV power lines due to the design network features. Networks up to 1 kV are usually performed with solidly grounded neutrals, in contrast to MV networks performed with isolated neutrals and unsusceptible to SC to ground. Therefore, the calculations for determining the quantity and locations of sectionalizing units in PTLs of 10 kV and above do not take into account a restriction on the placement of SU on a power transmission line that is associated with ensuring the sensitivity of the protective device installed at the beginning of PTL. In the proposed methodology for SU allocation, this criterion is considered and adopted as a decisive one, which is its advantage along with taking into account the direction of its use in LV networks.  
The second important criterion is power supply reliability improvement based on a decrease in the time of power supply outages, hence loss minimization from damage caused by electricity undersupply. Despite the fact that many of the above methods for SU allocating in electric networks highlight the economic component, the second advantage of the developed methodology is to determine the economic effect of reducing both the duration of emergency outages and the duration of scheduled repairs, taking into account capital and operating costs for equipment. In addition, in the current work, we consider the experience of using SU in 0.4 kV networks and the results of this experience in terms of reducing the power supply restoration time by more rapid information receipt about a failure and a more accurate determination of the search area for damage.  
The current paper has been organized in the relevant sections. Section 1, 'Introduction', is devoted to a literature review on research in the field of impact of power line sectionalizing on power supply reliability and allocation problem of sectionalizing units within electrical networks. The experience of design of sectionalizing unit devices and their introduction in 0.4 kV networks are described in Section 2. Section 3 describes criteria for the proposed methodology for SU allocation in 0.4 kV power transmission lines. Section 4 contains the application results for the proposed methodology on a case study. The final conclusions are drawn in Section 5.