Major Disturbance in UCTE system

Author: Clare Duffy, ESBI, Ireland

Summary of Disturbance

The Union for the Coordination of Transmission of Electricity (UCTE) grid suffered a severe disturbance on 4 November 2006. Immediate action by TSOs prevented a Europe-wide blackout. This article summarizes the findings (http://www.ucte.org) from the subsequent UCTE investigation.

E.ON Netz was requested to disconnect the double circuit 380kV line Diele-Conneforde in Northern Germany on 5 November at 01:00. E.ON Netz's empirical analysis showed no violation of the N-1 (The N-1 security rule aims at avoiding cascading effects and requires that a single incident should not jeopardize the secure operation of the interconnected network) criterion from the proposed switching in its network. On the 27 October E.ON Netz provisionally approved the switching request and informed neighboring TenneT and RWE TSO. Results of their N-1 analysis confirmed that the grid would be highly loaded but secure.

The manual switching of the Diele-Conneforde line on the 4 November caused increased power flow on the Landesbergen-Wehrendorf line (interconnection between E.ON Netz and RWE TSO). Action taken to remedy the situation actually deteriorated line loading eventually causing it to trip. This triggered cascade tripping splitting the UCTE synchronously interconnected grid (which covers 23 countries across Europe) into 3 islands (West, North East and South East - see figure 1) causing significant power imbalances in each island. Initial power imbalances in the West induced a severe frequency drop interrupting power supply to more than 15 million West European households. Sufficient generation reserves in the under-frequency areas (West and South East) allowed restoration of normal frequency in a relatively short time.

Lack of control over generation units (quick reduction of schedules and automatic reconnection of wind generation) in the over-frequency area (North East) contributed to a deterioration of system conditions in this area (long lasting over-frequency and severe transmission line overloading) and complicated the process of restoring normal system conditions.

Full resynchronization of the 3 islands was completed 38 minutes after the system split and normal conditions were restored in all European countries in less than 2 hours.

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