## 4 Blackout Analysis
### The Almost Pan European Blackout on 8 January 2021  
An event like the one in November 2006 occurred in January 2021. The European electrical system narrowly avoided a widespread collapse on 8 January 2021, when a major frequency disturbance occurred that may have paralyzed Europe. Several transmission network components were out of order in a short period of time, causing the synchronous European power system to be split into two different regions [79], as shown in Figure 5. The system separation caused a total power imbalance of about 6.3 GW, with a power shortage in the northwest and a surplus in the southeast. Within roughly 15 s, the frequency in Northwestern Europe dropped to 49.74 Hz. After that, the frequency settled at 49.84 Hz. Southeastern Europe's frequency first rose to a maximum of 50.6 Hz and then stabilized at 50.2-50.3 Hz (see Figure 6).  
\begin{table}
\begin{tabular}{l c c c c c c c c c} \hline
**Blackout** & \multicolumn{5}{c}{**Preconditions**} & \multicolumn{5}{c}{**Initiating Events**} \\ \cline{2-10}
**Name** & **PREC\_1** & **PREC\_2** & **PREC\_3** & **PREC\_4** & **PREC\_5** & **PREC\_6** & **PREC\_7** & **INIT\_1** & **INIT\_2** & **INIT\_3** & **INIT\_4** \\ \hline _IT\_2003_ & & ✓ & ✓ & & & ✓ & ✓ & & \\ \hline DK\_SE\_2003 & ✓ & ✓ & & & ✓ & ✓ & ✓ & ✓ & & \\ \hline GR\_2004 & ✓ & ✓ & ✓ & & & & & ✓ & & \\ \hline DE\_2005 & & & & ✓ & & ✓ & & ✓ & & \\ \hline EUR\_2006 & & & ✓ & & & ✓ & & & ✓ & \\ \hline AN\_2007 & & & & & & ✓ & & & ✓ \\ \hline PL\_2008 & & & & & ✓ & ✓ & & ✓ & & ✓ \\ \hline UK\_2009 & & & & & & & & & & ✓ \\ \hline AN\_2015 & ✓ & ✓ & & & & & ✓ & & & \\ \hline TR\_2015 & & ✓ & ✓ & & & ✓ & ✓ & ✓ & & \\ \hline UA\_12\_2015 & & & & & & & & & ✓ \\ \hline GR\_2021 & ✓ & ✓ & & & & ✓ & & & \\ \hline \end{tabular}
\end{table}
Table 4: Preconditions and the initiating events for all the major blackouts that occurred in Europe in the past 20 years.  
Figure 5: Continental Europe map displaying the two distinct regions on 8 January 2021.  
Following a short period of time, the frequency deviation was contained to a variation of about 0.1 Hz in Northwestern Europe thanks to the quick cooperation of interruptible services in the French and Italian TSOs. The 400 kV bus bar coupler trip in the Croatian network (Ernestinovo Substation) was the initial event, according to the analysis carried out by the Expert Investigation Panel of ENTSO-E [79]. Electric power flows were diverted to nearby lines, which were then overloaded because of the Ernestinovo substation's separation of flows. Due to overcurrent protection, the transmission line Novi Sad-Subotic tripped at 14:04:48.9. Following this, lines continued to trip due to distance protection, which ultimately caused the system to separate into two parts at 14:05:08.6. Figure 7 shows the precise positions of the components that tripped in the transmission system.  
Elements in generation, transmission, or distribution must be able to operate in a range of frequencies, without disconnecting from the network, for the minimum time periods listed in Table 5, according to [80]. During this event, there were several automatic disconnections that should not have occurred. Due to over-frequency (more than 300 mHz), in SE Europe, 3292 MW of generation tripped (187 MW in Bulgaria, 1350 MW in Greece,  
Figure 6: European frequency during the event on 8 January 2021.  
Figure 7: Location of the main transmission system elements that have tripped.  
600 MW in Serbia, and 1155 MW in Turkey). The 3292 MW total includes 587 MW in the distribution system. Additionally, a 50 MW load disruption was reported in Bulgaria. The southeastern region had a sizable generation disconnection, especially in Turkey and Greece. Since both countries were exporting energy before the incident but quickly turned into substantially energy importing regions after it, those two systems were on the verge of becoming the third or fourth islands of Europe.