Southern Sweden and Denmark, 23 September, 2003
At 12.35 pm on 23 September 2003 electricity supplies in much of Southern Sweden and Eastern Denmark were interrupted following a series of events in the southern swedish grid. At 12.30pm the Oskarshamn nuclear power plant tripped resulting in the loss of 1200 MWe to the grid. Five minutes later a failure in a sub-station resulted in two units of the Ringhals nuclear power plant also going off line with the loss of a further 1800 MWe. A total loss to the grid of 3000 MWe or about 20% of Sweden's electricity consumption at the time. This loss of power was the direct cause of the blackout which affected some 4 million businesses and homes. A description of the sequence of events can be found on the Elkraft website.
At the time of these events a number of Swedish generating stations were offline for maintenance while at the same time connectors to Poland and Germany from Denmark, including the Kontek Link, were also disconnected for maintenance and inspection though connections to northern Sweden, Norway, Zeeland and other parts of the Nortel grid were available.
Key to an understanding of the background to this event is the fact that southern Sweden and Eastern Denmark are so closely interconnected as to constitute a single grid region and the whole of this region was ultimately hit by the voltage collapse following the loss of 3000 MWe power.
Power was progressively restored in Denmark between 13.45pm and 19.05pm. The problem at the Swedish substation which had knocked Ringhals offline was repaired by the morning of 24 September.
Elkraft - description of the causes of the blackout.
Svenska kraftnät - Swedish grid operator