Separation of the Iberian Peninsula from the UCTE System - Grid frequency in Spain drops to 48.66 Hz in places on 24.07.2021
On 24.07.2021 at 16:36 (CEST), the Iberian Peninsula was disconnected from the European UCTE power grid. At our measurment inut in Lleida (North of Spain) the grid frequency dropped to a remarkable 48.66 Hz, in Malaga (South of Spain) the frequency dropped to 48.99 Hz - still a frequency difference of about 340 mHz! The difference to the nominal frequency of 50 Hz was thus about 1.4 Hz.
ENTSO-E/ the German TSO Amprion published a Tweet shortly after the resynchronisation of the system that the incident for the split is under investigation (Amprion tweet). Shortly after, ENTSO-E informed that the reason might have been a forest fire along one of the French-Spanish tie lines (ENTSO-E publication). Following the news, an airplane has damaged lines between France and Spain. This resulted in a power loss in large regions of Spain and Portugal (Bayrischer Rundfunk, SRF).
The following graph displays the corresponding load flow between France and Spain.
Before the split, a continuous flow from France to Spain above 2000 MW occurred over the day. With the system split in the hour between 16:00 and 17:00, the flow dropped to 0 MW. Interestingly, ENTSO-E published a load flow in the subsequent two hours also close to 0 MW (in the opposite direction). This is surprising as reconnection of the Iberian Peninsula took place shortly after 17:09. Unclear is also why no forced line outage has been published by the French TSO RTE nor the Spanish TSO REE (even not one day after the incident, Update: the publication occurred on 26/07/21).
Inciting the fault at 16:35:24?
We suspect that the disturbance was triggered a few seconds earlier, see the small, short frequency disturbances recorded by our measuring device in Lleida starting at 16:35:24 (CEST).
Automatic load shedding after 5 s
When strong negative frequency deviations occur, as in the case here, there is a massive power shortfall in the affected network section. Since generation and consumption must be balanced to maintain a stable frequency, in such cases only an automated load shedding remains to bring the frequency back close to the target range. Load shedding is therefore a kind of adrenaline injection for the system - this prevents a further drop in the grid frequency and thus possibly a blackout due to underfrequency. If the grid frequency drops too far too fast, the power plants will disconnect from the grid at a certain threshold, resulting in a blackout!
Interconnection of the two networks
The interconnection of the Iberian Peninsula with the rest of the UCTE network took place despite a considerable frequency difference of about 220 mHz difference! Subsequent to the interconnection, there are considerable power and frequency oscillations. We let a picture speak for itself here:
Based on the rule of thumb 1 GW generation deviation produces a frequency deviation of approx. 50 mHz, in the case of the aforementioned frequency deviation of over 220 mHz between the two grid sections, a compensation power of approx. 4 GW must have flowed, this could explain the subsequent oscillations after the interconnection. This would also explain the brief sharp drop in frequency at our Southern French measuring device in Aignan.
We expect that these oscillations also caused the 1010 MW forced unavailability of the Hydro Pump Storage plant La Muela near Saragossa close to the French-Spanish border 10 minutes after resynchronisation.
As soon as we have more information or have analysed it, we will publish more here.
Please note that Gridradar automatically informs you in realtime about such critical system effects. Thus, you are always up to date and could also use this service to prepare your production or consumption units or industrial production units for such grid irritations. Please have a look into our API description and its functionalities.
Please don't hesitate and get in touch with us in case of questions or suggestions: info@gridradar.net.
As of 26/07/2021 at 09:00