The main problem of electric utilities around the world is to ensure continuous power supply to consumers. One of the causes of power outages and blackouts can be geomagnetic storms during periods of the increased solar activity. They arouse geomagnetically induced currents (GICs) flowing in the long-distance high-voltage power grids on Earth’s surface. The history of this phenomenon investigation shows that GICs during strong geomagnetic storms had led to blackouts in certain regions of Canada, Sweden and the USA. To study these phenomena and assess the risks of such accidents for the regional system, a GICs registration system in 330 kV autotransformers neutrals of the Kola-Karelian power transit was developed in northwestern Russia. During 11 years of monitoring numerous cases of the flow of high values of quasi-dc currents with different time durations, induced by variations of the geomagnetic field, have been registered. In order to analyze the currents a wavelet transform was chosen, since this method allows to define not only the frequency composition but also changes in spectral characteristics over time, which is significant in the study of GIC. The paper presents a discussion of GIC scalograms obtained for four events of Solar Cycle 24: 13-14 November 2012, 17-18 March 2015, 7-8 September 2015 and 7-8 September 2017. The analysis showed that the characteristic duration of the peak of the considered GICs is from 4.6 to 11.1 min.

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