On Thursday, 10 January 2019, shortly after 9 p.m., a deviation from the 50Hz mid-frequency was registered in the Continental European (CE) power system, which comprises the synchronised transmission grids of 26 countries. The deviation lasted 9 seconds and, with a drop to 49.808Hz, was the largest absolute frequency deviation since the so-called “European Blackout 2006”, when the frequency reached 49.0Hz.
Thanks to immediate collective action by the transmission system operators (TSOs) of the CE Regional Group the underfrequency was quickly rectified and the European security of supply was not compromised at any moment. In concrete terms, the activation of CE reserves and of interruptible contracts with French industrial customers returned the situation to normal. To identify the root causes of the incident, the European Network of Transmission System Operators for Electricity (ENTSO-E) undertook in-depth investigations and has now released a detailed and transparent technical analysis.
According to this report, the large drop was caused by the superposition of two factors. A significant deterministic frequency deviation (DFD) during the evening peak load encountered another, unpredicted one, registered between 9 and 11 January and caused by a technical error resulting from a frozen measurement on four connecting lines between Austria and Germany. The cumulative effect of the permanent frequency deviation from 9 to 11 January and the significant evening DFD on 10 January led to the frequency loss in the interconnected CE system.
The ENTSO-E technical report indicates that solutions for DFDs in the CE region need to be found. DFDs have been observed for years, but are now becoming more common and are of greater amplitude due to imbalances between generation and demand. Possible solutions to DFDs may require a change in operating and/or market rules. ENTSO-E will make further enquiries in close dialogue with all interested parties.