The Italian 2003 blackout

TLDR

A fault on Swiss lines overloaded interconnections, triggering cascading outages that separated the Italian system from the UCTE grid, causing a frequency drop and insufficient load shedding that led to the 2003 Italian blackout. The study aims to describe the pre‑fault operation and key events that triggered the blackout, identifying the main causes of the Italian system’s separation and collapse. It also examines how the Italian automatic load‑shedding procedure misoperated, contributing to the failure to prevent the blackout.

Abstract

On September 28th, 2003, at 3:01 a.m., a fault on the Swiss power system caused the overloading of two Swiss internal lines close to the Italian border. The interconnection lines were heavily loaded by the large power import and the coordination between the system operators was not sufficient to mitigate the overload. The consequent loss of those important branches caused cascading outages of the lines interconnecting the Italian system and the remaining part of the UCTE (Union for the Coordination of the Transmission of Electricity) system. This resulted in a very sudden loss of synchronism between the Italian system and the UCTE grids, causing the loss of the whole import. The consequent power unbalance caused the frequency in Italy to decline; the automatic load shedding procedure was not able to shed load enough to balance the generation and the load, and this resulted in the blackout. The paper provides a short description of the pre-fault system operation and of the main events that triggered the blackout, identifying some of the main causes that resulted in the separation of the Italian system and the blackout. In addition, issues related to the misoperation of the Italian automatic procedure to prevent the blackout are discussed.