Geomagnetically induced currents (GIC) are a phenomenon well known for its negative effects on the operations of power systems. To efficiently mitigate them requires different types of the power system modelling, from GIC to alternating current (AC) harmonic generation, to 3-dimentional finite-element models of transformers.

Initiated by variations of the geomagnetic field in the presence of the conductive earth, i.e. the geophysical variables characterized by continuous frequency spectra, GIC and harmonics also exhibit continuous spectra. In order to adequately estimate their variations for mitigation purposes, the analysis on the impact of spectral frequency content on GIC and harmonics characteristics is required.

The presented study is based on the geomagnetic measurements and the power network data (i.e. GIC and harmonics) with high sampling rates recorded during two geomagnetic storms, 31 March 2001 and 26-27 July 2004. Availability of data covering both the source and the result of geomagnetic storm impacts on power grid allows to (1) analyse the influence of spectral content on sufficient representation of both geomagnetic and geoelectric variations during the intervals with significant raise in GIC and harmonics (such as rapid variations during Storm Sudden Commencement and storm itself), and to (2) justify the choice of the sufficient resolution of data by the network response presented as GIC and harmonics variations. In summary, the optimal resolution is suggested and the deficiencies associated with the under-representation of the geomagnetic spectrum are identified and discussed.