International experts confirm ČEPS analysis, last year's blackout was a combination of events

The widespread power outage affecting part of the Czech Republic in July last year was, according to a group of international experts, a combination of several mutually independent technical and operational events. The experts' investigation findings are therefore consistent with last year's investigation by Czech transmission system operator ČEPS. To prevent similar incidents, the experts also recommended tightening certain grid operating standards, expanding preventive measures and reviewing some procedures. ČEPS announced this today.

The massive power outage of 4 July last year, which lasted several hours, affected around one million customers. There are 6,3 million metering points in the Czech Republic. According to the investigation findings presented by ČEPS at the end of last year, the main cause was a cable falling onto the V411 line, caused by an earlier faulty repair. Further outages followed. According to ČEPS, the system had not been overloaded beforehand.

The ENTSO-E expert panel, tasked with independently examining the causes of last year's outage and proposing measures, comprised representatives of transmission system operators, European and national regulatory institutions, and regional coordination centres.

"The conclusions of the international expert panel correspond to the findings of the investigation that ČEPS published in its final report last year. They also confirm the importance of a number of measures whose implementation we began immediately after the extraordinary event," said ČEPS Vice-Chairman of the Board Svatopluk Vnouček.

The expert panel also issued recommendations focused on operational management, data and model quality, support for control room operators' decision-making, crisis preparedness and further development of technical infrastructure. These include tightening reliability standards in operational planning and preparation, expanding the use of so-called redispatching and other preventive measures, extraordinary inspections of selected transmission system lines, introducing additional diagnostics after emergency repairs, reviewing protection settings at selected generation sources, expanding joint training for control room operators, distribution system operators and electricity generators, and strengthening crisis communication and information systems.

ČEPS said it had already focused on a number of areas in recent months. "The security of transmission system operation is our highest priority. Together with our partners, we will continue to examine the Expert Panel's conclusions in detail and use them in the further development of our procedures, tools and infrastructure," Vnouček added.

According to earlier information from ČEPS, the outage began with the fall of a phase conductor, which took the V411 line out of service. The line is used to transmit high outputs from power plants and carry electricity over long distances. According to the system operator, the fall was caused by an incorrectly performed repair of a tension joint with a hidden defect. At the same time, output in the grid also declined and other generation sources with a total capacity of around 470 megawatts in the north-western Czech region stopped operating.