UCTE releases detailed Final Report on the disturbances of 4 November 2006 with recommendations on standards, procedures, tools and rules

30 January 2007

The events in the evening of 4 November 2006 are the most severe disturbance in the history of UCTE. However, the decentralized responsibilities of UCTE member TSOs demonstrated their efficiency. An Investigation Committee was set-up immediately after the incident; less than 3 months later UCTE issues a complete report with a detailed description of the sequence of events, an analysis of main causes and critical factors and the formulation of precise recommendations.
UCTE will report at the end of 2007 about the implementation of the recommendations.

On 4 November 2006, a severe frequency drop in the Western part of the UCTE grid caused an interruption of supply for more than 15 million European households. A number of high voltage lines in northern Germany tripped due to the reaction of automatic protection devices. The triggering event started at around 22:10 hours.

Until the switching-off of the 380 kV double circuit line Conneforde-Diele (DE), the system was in a state that complied with the current security standards. The severe disturbance on 4 November 2006 and the splitting of the interconnected system were not caused by some extraordinary climatic conditions or technical failures. The disturbance was triggered by causes in the E.ON Netz control area and the very rapid splitting of the interconnected system could not have been stopped once the cascading tripping of the lines started.

It led to a split of the UCTE system in 3 areas. In the two under-frequency areas (West and South-East), sufficient generation reserves and load shedding allowed restoring the normal frequency within about 20 minutes. The imbalance between supply and demand resulting from the splitting was further increased in the first moment due to a significant amount of tripped generation connected to the distribution grid. In the over-frequency area (North-East), the lack of sufficient control over generation units contributed to the deterioration of system conditions in this area (long lasting over-frequency with severe high voltage transmission lines overloading). Generally, the uncontrolled operation of dispersed generation (mainly wind and combined-heat-and-power) during the disturbance complicated the process of re-establishing normal system conditions.

Due to the adequate performance of the automatic counter-measures in each individual TSO control area and additional manual actions by TSOs a few minutes after the splitting, a further deterioration of the system conditions and a Europe wide black-out could be avoided.

Full resynchronization of the UCTE system was completed 38 minutes after the splitting and the TSOs were able to re-establish a normal situation in all European countries in less than 2 hours. The decentralized responsibilities of TSOs and their individual defence plans have demonstrated their efficiency.
The Final Report (see http://www.ucte.org) identifies the following findings.

The growing market activities and the fast and successful development of regional intermittent energy generation with low predictability (wind power) led to significant increase of cross-continental power flows. Even though the grid was originally developed for mutual assistance, it has now become the platform for shifting ever increasing power volumes across the continent. Against this background, grid operation has become much more challenging.

Main cases:

• Non fulfilment of the N-1 security criterion
• Insufficient inter-TSO coordination

Critical factors:

• Generators related issues – TSOs’ access to real time generation data, uncontrolled actions of generators, technical requirements for power plants
• Limited range of actions available to dispatchers for handling grid congestions
• Transmission/Distribution coordination in the context of defence and restoration plans
• Further reaching coordination of TSO resynchronization procedures
• Training of dispatchers

Based on the lessons learnt from the disturbance, the following recommendations are identified:

• The application of the N-1 criterion in the rules of the UCTE Operation Handbook will be reviewed
• The rules on emergency operations will be extended with a “Master Plan” defining principles of operation and TSOs’ responsibilities to manage UCTE-wide or regional disturbances
• UCTE will develop standard criteria for a regional and an inter-regional TSOs co-ordination approach aiming at improving the regional security management (from planning to real time)
• UCTE will set up an information platform allowing TSOs to observe in real time the actual state of the whole UCTE system in order to quickly react during large disturbances
• The regulatory or legal framework has to be adapted concerning the control over generation output, requirements to be fulfilled by generators connected to the distribution grid, schedules and their changes and access to online data of generators connected to the distribution grid.
  UCTE will provide at the end of 2007 a report informing about the status of implementation of the recommendations.