Correlation of Anomaly Rates in the Slovak Electric Transmission Grid with Geomagnetic Activity

The induction of electric currents in electric power distribution networks is a well-known effect of Earth-directed eruptive events. Inspired by recent studies showing that the rate of power-grid anomalies may increase after exposure to strong geomagnetically induced currents in mid-latitude countries in the middle of Europe, we decided to investigate such effects for Slovak electric-power distribution grid managed by the Slovak Electricity Transmission System (SEPS). We obtained a list of disturbances recorded in the maintenance logs by the SEPS company technicians with their dates and other details. Working with unadjusted data we found unexpectedly strong seasonal variations of failure rates. We show that this is a consequence of the strong dependence on meteorological conditions. In particular, mean temperature showed the strongest correlation with anomaly rate, while precipitation amount was just a little weaker in terms of the correlation. After the suppression of the meteorological dependence in the failure-rate series, we obtained a new temperature-independent dataset. Using this clean dataset we found an increase in failure rates in the periods of maxima of geomagnetic activity compared to the adjacent minima of activity.