Immediate and delayed responses of power lines and transformers in the Czech electric power grid to geomagnetic storms
Résumé
Eruptive events of solar activity often trigger abrupt variations of the geomagnetic field.
Through the induction of electric currents, human infrastructures are also affected, namely the equipment
of electric power transmission networks. It was shown in past studies that the rate of power-grid anomalies
may increase after an exposure to strong geomagnetically induced currents. We search for a rapid response
of devices in the Czech electric distribution grid to disturbed days of high geomagnetic activity. Such disturbed days are described either by the cumulative storm-time Dst or d(SYM-H)/dt low-latitude indices
mainly influenced by ring current variations, by the cumulative AE high-latitude index measuring substorm-related auroral current variations, or by the cumulative ap mid-latitude index measuring both ring
and auroral current variations. We use superposed epoch analysis to identify possible increases of anomaly
rates during and after such disturbed days. We show that in the case of abundant series of anomalies on
power lines, the anomaly rate increases significantly immediately (within 1 day) after the onset of geomagnetic storms. In the case of transformers, the increase of the anomaly rate is generally delayed by 2–3 days.
We also find that transformers and some electric substations seem to be sensitive to a prolonged exposure
to substorms, with a delayed increase of anomalies. Overall, we show that in the 5-day period following the
commencement of geomagnetic activity there is an approximately 5–10% increase in the recorded anomalies in the Czech power grid and thus this fraction of anomalies is probably related to an exposure to GICs.
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