## 4 Blackout Analysis
### Scenarios with Different Initial Condition before the Event on 8 January 2021  
Several scenarios for the European system could be written and analyzed using power flows, such as if there were different productions from the thermal units, if renewables participated to a greater extent, if the event had occurred during the evening peak, etc. However, the results of these power flows may be inaccurate because there were unwanted operations that happened during the event, as discussed earlier, and which are not taken into consideration during the execution of these flows. These unwanted operations (e.g., power trip units in frequencies in which they should not trip) need further investigation. Trips of power units may have helped the areas that were in over-frequency and made it more difficult to restore in the other part with the under-frequency. The question that can be reasonably asked is why this happened, what would have happened if the frequency had been disturbed even more, and whether the TSOs have the necessary oversight of the way the generating units are operating and whether they should step up efforts to their better and more reliable operation. From this, we can conclude that if the transfer of energy was greater than 6.3 GW from one side of Europe to the other, we would have (1) probably a greater number of units that would have tripped and (2) possibly internally in the regions with a different frequency, cascading on transmission lines, creating more areas with different frequencies or, in the worst-case scenario, a general blackout in half or all of Europe. Another aspect that needs further investigation is what would have happened if there were different power flows between countries due to the European electricity market. For example, on the day of the event, Greece was exporting energy to neighboring countries, when usually in this period, Greece was importing. Therefore, on 8 January 2021 and after the event due to the over-frequency, the power flow with other countries changed direction and the power flew to Greece, increasing ACE to 1300 MW. What would have happened in the same incident if Greece was importing energy, and due to the over-frequency, another amount of energy was added to the interconnections? Could it cause these power transmission lines to overload and trip after some time? Could this situation have caused a general blackout in Greece? In Table 6, an outcome of this scenario is depicted. These questions need further investigation and we can conclude that a blackout can happen at any time in a country or a wider European region. Due to the fact that there is always this possibility, every TSO must be prepared to face such an event, as we analyze in the next section. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Synchronous Area** & **Frequency Range** & **Time Period for Operation** \\ \hline \multirow{4}{*}{Europe} & 47.50–48.50 Hz & It is specified by each TSO (not less than 30 min) \\ \cline{2-3}  & 48.50–49.00 Hz & It is specified by each TSO (not less than the period for 47.50–48.50 Hz) \\ \cline{2-3}  & 49.00–51.00 Hz & Unlimited \\ \cline{2-3}  & 51.00–51.50 Hz & 30 min \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Frequency range and operation time period for demand and generation facilities in Europe.