The report into the worst disturbance in the history of UCTE finds that a severe frequency drop in the Western part of the UCTE grid caused a supply interruption for more than 15 million households. The triggering event was the switching-off of the 380 kV double circuit line Conneforde-Diele (DE) in the E.ON Netz control area to allow passage of a ship. A number of high voltage lines in northern Germany tripped due to the reaction of automatic protection devices and the very rapid splitting of the interconnected system into three areas could not have been stopped once the cascading tripping of the lines started, the report concludes.

In the two under-frequency areas, sufficient generation reserves and load shedding allowed normal frequency to be restored within about 20 minutes. However, in the North-East, which suffered from over-frequency, the lack of sufficient control over generation units contributed to the deterioration of system conditions. Generally, the uncontrolled operation of dispersed generation, mainly wind and CHP, during the disturbance complicated the process of re-establishing normal system conditions, the report says.

In identifying causes the report finds that growing market activities and the rapid development of regional intermittent energy generation with low predictability such as wind power has led to significant increase of cross-continental power flows. Although the grid was originally developed for mutual assistance, it has now become the platform for shifting ever increasing power volumes across the continent and against this background, grid operation has become much more challenging, UCTE says.

Recommendations include developing standard criteria for a regional and an inter-regional Transmission System Operators (TSOs) co-ordination and setting up an information platform allowing TSOs to observe in real time the actual state of the whole system in order to quickly react during large disturbances.

UCTE also suggests that the regulatory framework has to be adapted concerning the control over generation output, requirements to be fulfilled by generators connected to the distribution grid, schedules and their changes and access to online data of generators connected to the distribution grid.

A report on the status of implementation of the recommendations is due at the end of the year.

In its own report into the event, the European Regulators Group (ERGEG) said that a lack of coordination between transmission companies was highlighted and called for urgent action at the European level. In its recommendations, the Regulators’ report places greater emphasis on the need for binding European security and reliability rules and for proper supervision.

The European Commission therefore intends to adopt essential common binding network security standards and enhance the coordination between TSOs to ensure effective real-time operation of the European grid. In addition, efforts should be made to have a gradual evolution towards regional system operators which requires effective unbundling.

Until the improvements of the regulatory framework will be realised, the Commission is urging TSOs to improve coordination and undertake the necessary investments to alleviate bottlenecks.

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