The 2003 Italy Blackout

Just after 3am on Sunday 28 September 2003, a 380 kV line carrying power from Switzerland to Italy tripped at 03:01 after a flashover to a tree. Attempts to close it again failed, and its load shifted onto neighbouring lines, overloading a second Swiss line that could tolerate the overload for only about 15 minutes. Italy was importing about 6,950 MW at 03:00.

The operators did not grasp the urgency. A request to cut Italian imports by 300 MW came about ten minutes after the first trip and took another ten minutes to carry out, which was not enough. At 03:25 the second line also tripped after a flashover, the remaining links to Italy opened about 12 seconds later and Italy was left on its own. Its grid held for two and a half minutes before frequency fell to 47.5 Hz and the system collapsed, apart from Sardinia and a few local islands that stayed supplied.

Supply returned in stages. Most of the north was back before 08:00, the centre around 12:00 and the rest of the mainland by 17:00, with Sicily last at 21:40, and the last customer was supplied after 18 hours and 12 minutes. The investigating committee, set up by the European grid association UCTE, found the system met its security rules before the first trip and that no storm or attack was involved; human, technical and organisational factors kept it from returning to a safe state. Operators afterwards lowered import limits towards Italy, agreed new coordination arrangements and began cross training dispatchers.