Investigating the Trip of a Transformer in Sweden During the 24 April 2023 Storm

Geomagnetically Induced Currents are unwanted currents that flow in large ground‐based conductive infrastructure and are a significant threat to bulk power grids. This susceptibility is increased at high latitudes due to the larger amplitude geomagnetic disturbances caused by the strong and dynamic auroral electrojet currents. In Sweden, there has been a record of disturbances connected to geomagnetically induced currents; the most documented was a blackout in Malmö, a city in southern Sweden, on 30 October 2003. However, on 24 April 2023, there was a transformer trip in the Bandsjö substation (near Sundsvall) around the time of enhanced space weather. In this paper, we investigate this event by studying the solar wind properties as well as geomagnetic disturbances. The study shows evidence that the transformer trip was caused by a strong geomagnetic disturbance in the morning sector. This was triggered by a high‐pressure sub‐structure within the interplanetary coronal mass ejection cloud, preceded by 2 hr of strong southward interplanetary magnetic field. Additionally, analysis of multiple ground magnetometers shows that the geomagnetic impact was highly spatially structured. Plain Language Summary Space weather is a field of research that connects the changing conditions on the Sun and around near‐Earth space to effects on human technology and health. Occasionally, eruptions on the Sun will release large blobs of plasma known as interplanetary coronal mass ejections that travel outward into interplanetary space. When an interplanetary coronal mass ejection reaches Earth, it will interact with the Earth's near‐space environment, for example, by distorting and compressing the Earth's magnetic field. The focus of this study is a space weather phenomenon known as geomagnetically induced currents, which are unwanted currents that flow in large ground‐based conductors. Geomagnetically induced currents are caused by the changing Earth's magnetic field during the Earth's interaction with an interplanetary coronal mass ejection. Here, we study a trip of a Swedish power transformer to determine if it was caused by space weather. After our analysis, we show strong evidence that it was related to GICs, and we can also trace the effect to a clear feature inside the interplanetary coronal mass ejection. Key Points An interplanetary coronal mass ejection cloud sub‐structure preceded by 2 hr of southward interplanetary magnetic field resulted in strong geoelectric field