Catalogue of high-impact low-probability disturbance scenarios in clusters of offshore wind farms

Offshore wind energy generation with HVDC transmission represents already a critical energy infrastructure in Germany and its share of the German electricity production is expected to rise to above 20 % in 2050. Currently, the corresponding HVDC grid connections points of the offshore wind farm (OWF) clusters in North Sea are in the vicinity of the originating point of the 2006 European blackout. Their capacities are close to the frequency containment reserve (FCR) of 3 GW in the whole ENTSO-E region. Accordingly, a sudden power loss at these points can trigger a wide spread outage within the German or European grid, especially if the FCR limit is violated. Motivated by the above mentioned, we have created a catalogue of high-impact low-probability disturbance scenarios of the OWF cluster infrastructure with HVDC connections in the German North Sea. We present here this catalogue where a single or more HVDC grid connection systems are affected. In this manner the scenarios describe both power losses beneath and above the FCR limit. The catalogue is accompanied by a quantitative characterization of some of the threats which can initiate the scenarios, with a special attention to ship collision with a OWF infrastructure and cable damage through ship anchors or fishing ship nets. Recent events, such as the ship collision with a wind turbine of the Gode Wind 1 OWF in 2023 and the damage of the subsea cable of the EstLink 2 HVDC link in 2024, confirm the validity of these scenarios. In this way, the scenarios can serve for the evaluation and improvement of the power system resilience defined as "the ability to limit the extent, severity and duration of system degradation following an extreme event". A numerical OWF cluster model and a simulation of one of the scenarios are also presented.

Keywords: critical energy infrastructure, offshore wind farm, high-impact low-probability, disturbance, HVDC.