European Grid Manager Attributes Blackout to 'Complex Sequence of Events'

The European Network of Transmission System Operators for Electricity (ENTSO-E) has preliminarily reported this Friday that the blackout on April 28 was due to a 'complex sequence of events'. It also notes that there were two periods of voltage and frequency oscillations in the electrical systems during the half-hour preceding the incident.

The association, responsible for the independent European investigation into the incident, stated in a communiqué that in the half-hour before the blackout, which occurred at 12:33 pm, there were two oscillations in power and frequency between 12:03 and 12:07 and then between 12:19 and 12:21.

According to ENTSO-E, 'the Transmission System Operators of Spain (Red Eléctrica) and France (RTE) took measures to mitigate these oscillations. At the time of the incident, there were no oscillations, and the electrical system variables were within the normal operating range'. It was noted that Spain was exporting 1,000 megawatts (MW) to France, 2,000 MW to Portugal, and 800 MW to Morocco.

The organisation indicated that the event began at 12:32:57, and in the 20 seconds that followed, a 'series of different generation trips' were recorded in southern Spain amounting to approximately 2,200 MW. 'In Portugal and France, no generation trips were observed. As a result of these incidents, frequency decreased, and an increase in voltage was observed in Spain and Portugal,' the preliminary report states, according to Europa Press.

Between 12:33:18 and 12:33:21, the frequency on the peninsula continued to fall to 48 hertz, triggering contingency plans in both Spain and Portugal. Concurrently, the alternating current networks between France and Spain successfully disconnected due to the loss of synchronisation. Thus, at 12:33:24, the 'complete collapse of the Iberian electrical system' occurred, and the high-voltage cables between France and Spain also ceased transmitting energy.

ENTSO-E highlighted that by 12:44, a first 400 kV line between western Spain and France was reactivated, and 20 minutes later, the interconnection between Morocco and Spain was operational.

From the start of the restoration until approximately 1:30 pm, several Spanish hydroelectric plants with 'black start capability' were activated to initiate system restoration. By 1:35 pm, the connection on the eastern flank of the Franco-Spanish border was reactivated.

Furthermore, at 4:11 pm and 5:26 pm, Spanish peninsular time, the two Portuguese power plants with black start capability managed to restart after 'previous unsuccessful attempts'. Subsequently, the first 220 kV line between Spain and Portugal received energy at 6:36 pm, accelerating the restoration of the Portuguese system. Additionally, at 9:35 pm, the 400 kV connection in the south of both countries was reactivated. Finally, the complete recovery of the transmission system was achieved in Portugal at 12:22 am on April 29 and in Spain around 4:00 am on the same day.

Meanwhile, the Ministry for the Ecological Transition and the Demographic Challenge considered it 'good news' that progress has been made in analysing the causes of the blackout and that initial estimates of generation losses have been provided. Additionally, it 'welcomed' the appointment of the panel of experts who will lead the independent investigation by ENTSO-E.