Overview of the events and causes of the 2003 Italian blackout

During the night of September 28th, 2003 the European interconnected grid faced a series of outages, which started with line flashovers to trees and line trips on the Swiss electricity transmission grids, close to the Italian border, and ended with the separation of the entire Italian system from the UCTE (Union for the Co-ordination of the Transmission of Electricity) grid. The interconnecting lines were already heavily loaded and the operator action was not sufficient in controlling the situation. Due to the large power unbalance following the separation, the Italian electrical system and a small part of the Swiss system, suffered an under-frequency transient. Unfortunately, the automatic load shedding procedure and the regulating action of generators were not able to avoid the blackout. The incident affected the whole peninsula (about 45 million people); full restoration took almost 19 hours. This paper provides a short description of the system operation right before the incident, and reports the main events that led to the blackout. The focus is put on some issues that have been identified as the main causes that resulted in the separation of the Italian system and in the blackout. Some issues related to the operation of the Italian defense plan and to the restoration process are also discussed, along with some countermeasures already in place