## 3 Results
Figure 9 does not show the cost of electricity from renewable energy sources; however, as evidence shows, its cost is 1.2-1.6 times higher than the cost of electricity from power plants producing \"expensive\" electricity. Figure 9: Comparison of costs for preventing cascading failure process and its development. As seen in Figure 9, managing the loading of power plants generating \"expensive\" electricity, along with DG facilities, is the most preferable approach both technically and economically. Meanwhile, the construction of a new 500 kV overhead PTL remains the costliest technical solution. The choice of optimal nodes for connecting DG facilities should rely on the results of multi-variant steady-state calculations in the EPS calculation scheme, with the modeling of all types of emergency disturbances, including double faults. We analyzed a cascading failure process and its development using the example of a real systemic accident characterized by a cascading nature that took place within one of the EPSs. This was necessary to demonstrate the performance of the algorithm designed to analyze the conditions for the cascading failure process and its development trajectories. Figure 10 demonstrates the superposition of a 3D graphic surface of the network parameter non-homogeneity on the EPS network topology before the moment of a short circuit in a 500 kV overhead PTL 1. The disconnection of the 500 kV overhead PTL 1 by the emergency trip system and by the emergency control devices, AT5 and AT2 (3 \(\times\) 167 MVA, 500/220/35 kV) and AT6 (250 MVA, 500/110/10 kV) in the 500 kV substation SS8 (Figure 10), resulted in a power surge in the 110-220 kV overhead PTLs. This led to a cascading failure of the overloaded components in the EPS network (Figure 11). Figure 10: A 3D graphic surface of the parameter non-homogeneity of the 500 kV network until the moment of short circuit in the 500 kV overhead PTL 1. Figure 12 shows a 3D graphic surface of the non-uniform distribution of current (\(I\), p.u.) in the EPS components during the development of a cascading systemic failure. In this visualization, branches are replaced by equivalents and the respective rated voltage values are indicated at the network nodes. The overload in the seventh step led to the disconnection of the network components, which caused the asynchronous mode (AM) in four 110-220 kV overhead PTLs. This  
Figure 11: Diagram of changes in current across branches with cascading tripping of network components under EPS blackout scenario. Figure 12: A 3D graphic surface of non-uniform distribution of current (\(I\), p.u.) in EPS components during cascading systemic failure development. process was interrupted by the automatic asynchronous mode elimination devices, tripping the PTLs. The active power shortage in the central part of the EPS was 866 MW. Switching to the island mode diminished the frequency to 47.47 Hz, which caused the disconnection of consumers with a total capacity of 967 MW in the analyzed EPS and a capacity of 83 MW in the neighboring EPSs by automatic underfrequency load shedding devices [86; 87]. Figure 13 presents a 3D graphic surface of the non-uniform distribution of the current (_l_, p.u.) after the seventh step of the cascading failure process resulting in the disconnection of the 220 kV overhead PTL 4. Simulation modeling performed for the step-by-step analysis of the sequence of quasi-steady states enabled the prevention of the transition of an emergency process to a cascading systemic failure since, in this case, emergency control devices were activated by unacceptable deviations in the power flow parameters in the EPS, leading to the disconnection of considerable volumes of consumers.