A cascading transmission system collapse affected large swathes of Western Europe recently after a problem in Germany spread to neighbouring countries, leaving millions without power.

According to the UCTE, the interconnected grid was affected by a serious incident originating in the North German grid that led to disruptions of supply mainly in the Western part of the system.

At about half past nine in the evening, both circuits of the 380kV Conneforde-Diele line in the control area of E.On Netz were switched off in order to allow a ship to pass along the Ems river in Lower Saxony safely. However, although following the switch-off energy was stably transferred to other lines in the South of the country a higher load appeared on the E.On Netz grid, notably on the line Wehrendorf- Landesbergen in East-Westphalia between the transmission systems of RWE TSO and E.On Netz.

At just past 10 the lines Wehrendorf-Landesbergen and Bechterdissen-Elsen tripped, further tie-lines were overloaded within seconds and tripped in cascade, leading to a split of the European UCTE interconnected network.

As a domino effect, a grid separation in Germany took place from North to South-East and spread over to Austria which was also split into two parts. Some five million people in France lost power mainly in the east of the country while Italy, Belgium and Spain were also affected.

In a statement E.On Netz said: “By immediate co-operation the European grid operators managed to stabilize the European grid within only half an hour and restored the electricity supply afterwards where outages had happened.”

The exact reasons for the failures are still being analysed as similar switching measures have been carried out several times without any problems.

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