Zero power on the grid. Now what?

It's the morning of 28 April. Operations are running normally at Endesa’s e-distribución grid control centres. The 5 control centres (in Seville, Zaragoza, Palma de Mallorca, Las Palmas de Gran Canaria, and Barcelona) are handling an electricity grid made up of nearly 1,100 substations and high-, medium-, and low-voltage lines. If we laid all those lines end to end, they would circle the Earth 8 times. The day’s focus is on performing the 450 scheduled tasks that are executed daily on the distribution network: new infrastructure, upgrades, maintenance, automation, etc.

The electricity system is operating normally. International connections, as well as the link with the Balearic electricity system, are up and running.

At 12:33 p.m., the blackout becomes a reality: 10.6 million e-distribución customers on the Spanish Peninsula lose power.

First steps in recovery: coordination and communication

The situation is immediately confirmed by the control centres in Andalusia and Extremadura, Aragon, and Catalonia. Meanwhile, the Balearic Islands, despite having lost connection with the Peninsular System, continue to operate normally using the available island-based generation. The Canary Islands, though disconnected from the peninsular system, report no issues.

Crisis protocols are activated: coordination teams are formed in each of the three affected regions in our grid, along with a central coordination team based in Madrid. We’re ready. The recovery process begins.

The first steps in restoring power look very different for each type of operator:

• The System Operator (Red Eléctrica, REE), responsible for ensuring an adequate balance between generation and demand in the electricity system, requests the activation of certain hydroelectric power plants, specifically those capable of starting up without electricity from the external grid. This process is known as a ‘black start.’ At the same time, REE begins segmenting the transmission grid into small islands, which can be energised once the power plants are ready to operate.
• The Distribution Network Operators (DNOs), also known as electricity distributors, play a very different role, focused on two main areas: communication with public authorities and priority customers, and preparing the distribution grid for a gradual restoration following instructions from the system operator.

They notify the Authorities (Autonomous Communities, Regional Government Offices, Regional Industry Offices, Municipalities) and emergency services (Civil Protection, 112) to set up coordination task forces. The planned recovery process is shared, along with estimated restoration times and an assessment of the expected impact. Additionally, they identify critical situations or special needs that must be addressed during the restoration process. For instance, the situation in hospitals is checked to ensure that their backup generators are up and running.

From 0 to 100: how the system was gradually reconnected

Once the system operator confirms that electricity generation is operational, initial voltages start to register in the small islands that have been created. When these islands are stable, the system operator instructs the distribution companies to start adding loads to the islands. At 2:00 p.m., 1% of customers have their power restored.

Gradually, the distribution companies receive instructions to reconnect their customers within the limits of maximum load increases, depending on each island’s generation capacity. At first, increments of 25 or 50 MW are allowed, and as the system stabilises, more power can be added in each step.

Other generation sources can be brought online with the help of the initial energisation. The load provided by the distribution side continues to rise. The system is restarting.

The system operator begins to connect the initial islands, which start spreading like oil stains across the country.

The process unfolds in an orderly, step-by-step manner, with the exception of a relapse in the southern area that forces a restart from zero.

By around 10 p.m., 50% of the affected customers have been reconnected,  with a stable grid that continues to progressively consolidate.

In Andalusia, the restoration of the electricity supply expands like an oil stain growing outward from Cadiz, spreading eastward toward the Malaga province and westward towards Badajoz. In Aragon, the restoration begins at the Navarre border, and in Catalonia, it starts from the interconnection with France, extending toward central Catalonia and the major consumption hub of Barcelona, including its industrial belt.

As the early hours of the morning go by, the restoration process speeds up and demand decreases. From its control centre, Aragon confirms that at 1:39 a.m., 100% of the market has been restored. Across the mainland territory served by e-distribución, 74% of customers have had their service restored by 2:00 a.m. More than 7.8 million households now have electricity.

Catalonia returns to normal grid conditions at 3:01 a.m. At this point, 8.5 million households are back to normal, 81% of the total affected.

In Andalusia, due to the initial relapse, the process is slightly behind schedule. Action was required on-site at substations that had lost remote communication, although auxiliary services still had enough power to continue operation. Staff worked through the night, at the control centres and out in the field.

By 11:00 a.m. on 29 April, 99% of the electricity supply had been restored. After a long day, normality returned to our cities.

A team of nearly 850 people committed to delivering an essential service

During the recovery process, especially in the most intense early hours of 29 April, almost 90 technicians from the control centres and approximately 750 personnel deployed across the peninsula worked in full compliance with operational protocols. Around 25,500 operations were carried out with no errors or safety incidents.

Besides the technical operation of the entire complex infrastructure, this exceptional situation once again demonstrated the commitment, dedication, service mindset, and professionalism of the numerous  e-distribución team, who worked tirelessly to manage the incident with a single goal: restoring normality for our customers. Each and every one of them feels the responsibility that comes with providing a vital service to our society.