Near-miss that could have sparked European blackout caused by trip in Croatia – response called from GB to Turkey

An electrical trip in a Croatian substation was the cause of a system event that called for action across electricity markets from GB to Turkey, according to a preliminary investigation by European transmission operators group Entsoe.

The event would have gone unnoticed by most customers, but it illustrates the importance of ensuring that plant connected to the electricity network can ‘ride through’ disturbances, instead of self-disconnecting and risking a cascade fault from a relatively small initiator. New GB regulations require plant to be set to aid system resilience and a programme currently provides funding to make the necessary changes, see more.

Europe has one of the largest ‘synchronous’ electricity systems in the world, covering an area from the English Channel to the Turkish network. It has non-synchronous connections with the Nordic and British Isles synchronous areas.

The incident lasted for an hour. At around 14.05 on 8 January the fault at the Ernestinovo substation split electric power flows in this substation. It shifted electric power flows to neighbouring lines which were subsequently overloaded. Shortly afterwards the synchronous system automatically split into two regions, northwest and southeast of a line crossing Romania and Bosnia Herzegovina.

As a result the southeast system had a 6.3GW oversupply of power, and frequency rose. The northeast area had an undersupply and frequency fell.  The change in frequency outside mandated limits could have caused automatic disconnections and cascade faults leading to blackouts.

In the northeast area demand customers with interruptible contracts were disconnected and 420MW and 60MW of supportive power was automatically activated from the Nordic and Great Britain areas, respectively. Frequency was restored within required limits by 14.09.

More measures were taken in the southeast area, including disconnecting a 900MW power plant in Turkey. Frequency remained less stable in the southeast, which is a smaller system than that in the northeast so has less stability when it operates on an island basis.

The two parts of the system were reconnected and operating as normal soon after 3pm.

Entsoe has now begun a formal investigation into the incident, the most important on the synchronous system since an event in 2006 that caused blackouts in Europe.

Further reading

£5k bonus for embedded generators who adjust plant ‘set points’ this quarter – and warning over mid-May deadline for full subsidy

Entsoe investigation into January event

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