15 January 2021, 17:44
Figure 1 - Map of Continental Europe showing the two seperated areas during the system event on 8 January 2021
At approximately 14:05 CET, the frequency in the North-West Area of Continental Europe initially decreased to a value of 49.74 Hz within a period of around 15 seconds. Afterwards, the frequency reached a steady state value of approximately 49.84 Hz. At the same time, the frequency in the South-East Area initially increased to a value of up to 50.6 Hz before settling at a steady state frequency between 50.2 Hz and 50.3 Hz. This can also be seen from the graph below.
Figure 2 - Frequency in Continental Europe during the event on 8 January 2021
Due to the underfrequency in the North-West Area, contracted interruptible services in France and Italy, in total around 1.7 GW, were disconnected in order to reduce the frequency deviation. These services are large customers who are contracted by the respective Transmission System Operators (TSOs) to be disconnected if frequency drops under a certain threshold. In addition, 420 MW and 60 MW of supportive power were automatically activated from the Nordic and Great Britain Synchronous areas respectively. These countermeasures ensured that already at 14:09 CET the frequency deviation was limited to a deviation of around ‑0.1 Hz in the North-West Area from the nominal frequency of 50 Hz (see Figure 2).
Due to the large overfrequency in the South-East Area, automatic and manual countermeasures were activated (i.e. the reduction of the feed-in of generation units) in order to stabilise the frequency. Thus, at 15.05 CET the frequency deviation in the South-East Area could be limited to +0.1 Hz from the nominal frequency of 50 Hz (see Figure 2).
The automatic response and the coordinated actions taken by the TSOs in Continental Europe ensured that the situation was quickly restored to normal operations. Actions were coordinated between the TSOs in order to reconnect the two areas as fast as possible again. Therefore, the contracted interruptible services in Italy could be reconnected at 14:47 CET and in France at 14:48 CET. At 15:08 CET, both areas were connected again to one synchronous area in Continental Europe.
ENTSO-E has kept the European Commission and the Electricity Coordination Group composed of representatives of Member States informed.
ENTSO-E is publishing today also questions and answers with regards to this event. All information published is subject to the results of a detailed investigation on the event which is ongoing. The investigation is following the legal framework under the Commission Regulation (EU) 2017/1485 of 2 August 2017 (System Operation Guideline) whereby National Regulatory Authorities and ACER are invited to join together with TSOs in the Investigation Panel.
In line with the provisions of the Commission Regulation (EU) 2017/1485 of 2 August 2017 (System Operation Guideline), ENTSO-E will present the results of the investigation to the Electricity Coordination Group and will subsequently publish them once the analysis is completed.