## 3 Results
A simplified feasibility analysis of various technical solutions was based on the specific cost indicators of FACTS devices, specific cost indicators of the 500 kV overhead PTL construction, and the cost of \"cheap\" and \"expensive\" electricity from operating power plants [84; 85]. The specific costs were employed to calculate the cost of the FACTS devices (Table 1) with a capacity of 1100 MVA, excluding the cost of construction and installation works (CIW), controlled series compensator (CSC), and unified power flow controller (UPFC). Let us calculate the cost of building a new 500 kV overhead PTL. The size of investment in the construction of 500 kV overhead PTL is determined on the basis of consolidated price standards (CPSs). The cost to construct 1 km of a 500 kV overhead PTL, utilizing wires with a cross-section of 500 mm\({}^{2}\) (with three wires per phase), is estimated at USD 0.202 million/km. Then, the cost of the overhead PTLs 8-9 (I\({}_{8-9}\) = 900 km), excluding design and survey work, is  
Figure 1:0  
For a real-world EPS scheme, studies were conducted to increase its survivability by changing power flows in the 500 kV network by adjusting the load of generating equipment at operating power plants. This facilitated the unloading of branches that had current values approaching the admissible limits during emergencies. The cost of the generated electricity in the calculations was as follows:  
* Electricity generated from power plants with a specific fuel consumption of 310 g.e.f./kWh and a cost of \(\mathrm{C}_{\mathrm{cheap}}\) = USD 0.039/kWh was considered cheap;
* Electricity generated from power plants with a specific fuel consumption of 650 g.e.f./kWh and a cost of \(\mathrm{C}_{\mathrm{exp}}\) = USD 0.055/kWh was considered expensive. Let us determine the total cost of electricity generation within an EPS when loading only power plants producing \"cheap\" electricity:  
Figure 1:1 \begin{table}
\begin{tabular}{c c c} \hline \hline
**Device** & **CSC** & **UPFC** \\ \hline Specific cost, USD/kVA & 45 & 120 \\ Cost of the device, million USD & 49.5 & 132 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Costs of FACTS devices. Figure 8: Graph of changes in currents in EPS branches during cascading failure process development. where \(\sum E=4748\) million kWh is the total annual electricity generation from operating power plants in the analyzed EPS. Throughout the year, power plants producing \"expensive\" electricity must be loaded during periods of maximum loads in the EPS. According to statistics, the generation of electricity from power plants with \"expensive\" electricity, which is necessary to prevent the cascading failures and their development, is \(\sum E_{\text{exp}}=617\) million kWh. Let us determine the total cost of generating electricity in an EPS given the partial loading of power plants producing \"expensive\" electricity, whose loading is necessary under certain topologies and operating conditions:  
\[\sum\text{C}^{*}= \sum E^{\prime}_{\text{cheap}}\cdot\text{C}_{\text{cheap}}+\sum E _{\text{exp}}\cdot\text{C}_{\text{exp}}=(4748-617)\cdot 0.039+617\cdot 0.055\] \[=161.109+33.935=\$195.044\text{ million}.\]  
The annual overpayment by consumers in the case of the partial loading of power plants producing \"expensive\" electricity is  
\[\Delta\text{C}=\sum\text{C}^{*}-\sum\text{C}=195.044-185.172=\$9.872\text{ million}.\]  
Figure 9 presents the results of a comparative feasibility study for preventing cascading failure processes and their development according to the scenario shown in Figures 7 and 8 in a test scheme of a 500 kV power system. Possible options for preventing the first step of the emergency cascade process by implementing circuit-mode measures aimed at increasing the survivability of the EPS were considered. Options for loading power plants with \"expensive\" electricity, using FACTS devices, and constructing a 500 kV overhead power line were considered measures allowing for the redistribution of power flows in the EPS.