“The initial cause of the recent blackout was the priming of the high-voltage substations at the Radès power plant, caused by a very high humidity of 90%,” said Hichem Anane, CEO of the Tunisian Electricity and Gas Company (STEG) said in an interview with TAP news agency Thursday.
“The STEG teams relied on the Algerian network, which is connected to Tunisia, to gradually restart the national production facilities.
On Tuesday night, a general power cut at 1.30 a.m. plunged Tunisia into a total blackout. Despite official statements citing technical reasons for the blackout, it sparked heated debate on social media?
More than 24 hours after the nationwide blackout, what exactly caused it?
In the immediate aftermath of the incident, STEG’s priority was to restore the power supply, and as soon as it was restored, our teams deployed across the country began collecting all available data from the network to identify the causes of the blackout.
Initial findings showed that the preliminary cause of the blackout was a fault in the high-voltage substations at the Rades power station, caused by very high humidity levels, which reached 90%.
This triggered the automatic shutdown of the three generating units at Rades, resulting in a loss of around 875 megawatts from these units against a total demand of around 3,226 megawatts.
The automatic defense plan designed to compensate for this loss was activated, but given the speed of the incident (4 seconds between the failure and the total blackout), the capacity of the other national generation plants (Sousse, Gabès, etc.) was exceeded and the frequency fell below the 47.5 Hz threshold, the authorized operating limit for the plants, resulting in the blackout.
A preliminary report on this incident, supported by recordings, photographs and all available technical data, will be published shortly.
How was the blackout restored?
Based on the experience of the 2014 blackout, our teams opted for the most time-saving solution and relied on the Algerian grid connected to Tunisia to gradually restart the national power plants.
The main objective was to rebuild the electricity system by restarting these power stations, checking the high-voltage lines and restoring the transmission system and the medium- and low-voltage distribution stations.
At around 03:35 on Wednesday September 20, 2023, we restarted the generation and transmission sections and began the gradual reconstruction of the rest of the system. By 6:00am, power had been restored to 95% of customers in the regional control centers, except in a limited number of areas where certain faults prevented automatic restoration and required manual intervention by our teams.
At around 12 noon, 99% of the system was operational, with the exception of certain areas (Lac, Ain Zaghouan, etc.), which were restored at around 10 pm.
Isn’t the energy deficit in Tunisia one of the reasons for the fragility of the electricity system?
The blackout occurred when total demand was around 3,226 megawatts, compared to an installed production capacity of around 5,400 megawatts. So, the blackout was not a generation capacity problem.
Today, our installed production capacity is theoretically sufficient to meet Tunisia’s needs, but as an electricity operator it does not give us enough margin to meet peak consumption periods such as the summer. Additional needs are currently covered by import contracts signed with Algeria, pending the implementation of programs to increase the capacity of our national power plants and better integrate renewable energy.
Some critics point to a lack of maintenance and upkeep of the electricity network as one of the possible causes of the blackout?
Having worked for STEG for 35 years, 10 of them at the Radés plant and another 10 as Central Director of Generation and Transmission, I can assure you that the maintenance of the plants and networks is an absolute priority for the company.
In the case of the generation plants, this is carried out under maintenance contracts signed with the manufacturers, under the supervision and control of STEG. Maintenance is carried out at regular intervals based on production volume. A combustion inspection is carried out every year, inspections of the hot section after every 20,000 hours of operation and a major inspection (general overhaul) after every 48,000 hours of operation.
The power transmission section is also systematically cleaned. The last cleaning was carried out a week before the incident at the Radès substation, but the sand wind that the country has been experiencing recently, combined with high humidity, was the cause of the incident.
The maintenance plan for 2023-2024 is already being implemented.
Are there any solutions to avoid such incidents in the future?
An international benchmark could easily show that this type of incident has also occurred in other countries, such as France and Italy, and that electrical systems, especially HV overhead substations, are sensitive to climatic hazards such as humidity. This is why STEG has decided to purchase armored substations in the future.
Moreover, history has shown that such incidents cannot be 100% avoided. In the event of a known peak in demand, we can either resort to periodic blackouts, which are programmed in advance with the parties involved, or increase import contracts, as was agreed with Algeria last year.
But in the event of an unexpected incident, planned action is no longer an option. In this case, automatic defense plans are triggered to try to balance supply and demand. To avoid this type of incident, we need interconnections with neighboring and other countries in addition to the national grid. Interconnections between European countries now help them to deal with problems of this kind.
On Wednesday, Tunisia was able to overcome the blackout by relying on the Algerian network (between 600 and 800 megawatts). Libya contributed 50 megawatts. Better interconnection between these countries could improve their ability to deal with this type of problem. In addition, the Mediterranean electricity interconnection project (ELMED) between Tunisia and Italy will improve Tunisia’s electricity security.
Has the economic cost of the blackout been estimated?
By 6am on Wednesday, almost 90% of the network had been restored. Priority was given to critical sectors (hospitals, sovereignty centers, industry, transport, SONEDE, households, etc.).
The economic impact was therefore not very significant. In addition, our teams in the various regions are currently assessing the direct damage suffered by manufacturers. This will be covered by our insurance.
