## 4 Case Study for SU Allocation in 0.4 kV PTLs According to the Developed Methodology  
Determination of SU Maximum Distance According to Criterion of Sensitivity Limits against Single-Phase SC  
A case study for testing the developed methodology for allocation of SUs in 0.4 kV PTLs in terms of sectionalizing units with different sets of functions was conducted in the 0.4 kV electrical network of the Mezenka village located in Oryol region, Russia. Mezenka village has 43 consumers powered by a 10/0.4 kV transformer substation through a power transmission line. A capacity of power transformer installed at the TS is 250 kVA. The protection of PTLs is carried out by an automatic switch (AS) with an operating current of 160 A and the sensitivity current \(I_{\_}s\) of 480 A. Power transmission lines are made with wires with a cross section of \(3\times 50+1\times 50\) mm\({}^{2}\). The length of PTLs with branch lines is 1.85 km.  
Table 1 presents the information on the calculations results of maximum length of PTLs with the wires of different cross-sections for cases when the PTLs are supplied from  
transformers with a capacity of 250 kVA. The calculations were based on the data presented in [38].  
In accordance with Table 1, the maximum length of a power transmission line in terms of the criterion of protection sensitivity in the case of Mezenka village is 0.29 km.  
Determination of SU Installation Location According to Criterion for Power Supply Reliability Improvement  
To assess the accuracy of the location choice for SU on the criterion for power supply reliability improvement, it is necessary to analyze the network configuration, data on electricity consumption by consumers connected to different network sections, and the importance of consumers. The diagram of power supply network of Mezenka village is shown in Figure 4.  
According to Figure 4, T is power transformer, QF1 is input automatic switch for 0.4 kV busbars, QF2 is automatic switch of outgoing PTL, L1.1-L1.8 are 0.4 kV PTL sections,  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{\(I_{\text{test}}\), **A.**} & \multirow{2}{*}{\(U_{\text{fp}}\), **V**} & \multicolumn{2}{c}{\(L_{\text{test}}\) for ABS2} & \multicolumn{2}{c}{\(L_{\text{test}}\) for ABS2} & \multicolumn{2}{c}{\(L_{\text{test}}\) for ABS2} & \multicolumn{2}{c}{\(L_{\text{test}}\) for ABS2} & \multicolumn{2}{c}{\(L_{\text{test}}\) for ABS2} & \multicolumn{2}{c}{\(L_{\text{test}}\) for ABS2} \\  & & **3 \(\times  
and S1-S43 are consumers. Among them, consumer S23 is an experimental greenhouse, and consumer S29 is a pumping station, interruptions in the power supply of which must be as minimized as possible. At the same time, consumers S30-S43 are residential buildings having low power consumption and not requiring increased PS reliability. In addition, the data on accident rate for PTL sections were assessed. They revealed that the PTL section supplying consumers S30-S43 is the most urgent; that is, damage occurs on it much more often than on other sections. Therefore, the location of SU installation was tentatively determined on the branch line (section L1.6, Figure 4) at a distance of 0.25 km from TS (closer than 0.29 km). According to the technical reports of the power grid company servicing the Mezenka network, the annual electricity consumption by the entire PTL powering the village is 227,800 kWh per year, whereas the annual consumption for SU installation location at a distance of 0.25 km from TS is 63,070 kWh per year. The estimated time of scheduled outages during a year is 7.16 h, while emergency power supply outage time amounts to 3.59 h, with the proportion of unstable failures accounting for well over half of all cases (60%). The damage caused by electricity undersupply for the entire transmission line is RUB 56,820 per year, that is, USD 757.6 at the exchange rate of USD 1.00 per RUB 75.00.