## 2 Design of sectionalizing Devices
It permits the SU to be remotely switched on. DRTU 6 receives signals to switch on or off SU using a coded signal transmitted through a communication channel, for example, JPS, JPRS, Glonass, radio, or another channel. Data on electricity consumption and on power quality are sent to DRTU 6 and through it to a dispatcher of power supply company or the company on whose balance SU equipment is located. The uninterruptible power supply unit (UPS 7) supplies power to CUSU 5 and DRTU 6 from both a power network and an independent power source contained in it, e.g., a battery or a capacitor. Thus, SU enables us to carry out the switching and protection of 0.4 kV power lines, electricity metering, power quality control, and control of the amount and duration of PS outages. Its application prevents the development of various emergency-based scenarios and provides a reduction in electricity undersupply for consumers, a reduction in losses of power supply company, and thus, an increase in the reliability and efficiency of power supply systems. Figure 3 presents an inside view of the sectionalizing unit on the basis of the block diagram presented in Figure 2.  
The main elements of the SU are a vacuum contact LSM/TEL-1/400-352 capable of switching device power circuits and a microcontroller control unit implementing the following functions:  
* Two-way communication between SU and a network dispatcher;
* Constant monitoring of voltage and current parameters;
* Control of the vacuum contact KM1 for automated (or remote) switching SU power circuits;  
Figure 3: Inside view of SU combined with electricity metering and power quality control. * Implementation of automatic (or remote) input or inhibit input of a reserve to an emergency PTL section (when using SU as a recloser);
* Automatic (or remote) control of automatic reclosing function;
* Providing an understandable interface and output of all information on a display for service personnel. The use of MCUSU-1 allows informing a network dispatcher about:
* Changes in current and voltage parameters;
* Position of vacuum contactor;
* Successful implementation of automatic reclosing function;
* Fact and duration of voltage interruption in circuits under monitoring. The cost of modernized SU amounts to USD 1173.6, which includes the cost of SU components and the cost of manufacturing, USD 973.6 and USD 200, respectively. The exchange rate of USD 1.00 is RUB 75.00. The capital investment in SU installation (C\({}_{cap}\)) will be USD 1467, consisting of SU cost, delivery costs (10-15% of SU cost), and installation costs (15-25% of SU cost). The operating costs of servicing SU for the year (C\({}_{op}\)) will be USD 90.64 and consist of depreciation, maintenance and repair costs, and other costs. Methodology for SU Allocation in 0.4 kV PTLs Based on Criteria of Sensitivity Limits and PS Reliability  
A methodology for determining the placement of sectionalizing units in 0.4 kV power networks is based on two criteria. The first criterion is the main one, fulfilling sensitivity limits against single-phase SC current. The fulfillment of this criterion is obligatory, since it allows a sectionalizing unit (recloser) to perform the main function, that is, to disconnect the line under protection in case of a short circuit. The second criterion is used to assess the economic effectiveness of protective devices' allocation in terms of the economic value of increasing power supply reliability minus the cost of investment and maintenance.