The 2006 European Grid Split

On the evening of Saturday 4 November 2006, both circuits of a 380 kV line in northern Germany were switched off so that a ship could pass safely along the Ems river. The shutdown had been planned for the early hours of the next day, but the time was brought forward and the neighbouring grid operators were told late. A routine simulation run in advance showed no problem.

At about 22:10 an operator at the Landesbergen substation tried to reduce the flow on a heavily loaded line by coupling busbars, and the move tripped the line instead. Other lines tripped one after another across the interconnected grid, which split into three separate areas. Frequency fell to about 49 Hz in the west, rose to about 51.4 Hz in the north east and dipped only slightly, to about 49.7 Hz, in the south east. In the west, automatic load shedding cut about 17,000 MW of consumption and 1,600 MW of pumps within seconds, which stopped the system collapsing.

More than 15 million European households lost supply. Operators began reconnecting the areas at 22:47 and had a normal situation back in all countries in less than two hours. The investigation named two main causes: after the manual switch-off the grid no longer met the rule that it must survive the loss of any single element, and the operators had not coordinated enough. It also found that many wind turbines and other generators on distribution grids tripped as frequency fell, and that some local network operators reconnected customers without coordinating with the transmission operators.