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The paper presents an analysis of test results by Frequency Domain Spectroscopy (FDS) of
the loss tangent (tgd) in electrotechnical pressboard impregnated with insulating oil and containingnanoparticles of water depending on the frequency of alternating current, sample temperature and degreeof moisture. We found tg dreduction in areas of low
and ultra-low frequency. It is associated with relax-ation due to the hopping conductivity (tunnelling) ofelectrons between moisture nanoparticles occurring in the cellulose impregnated with insulating oil. Infrequency areas close to the local minimum of tgd and higher, relaxation does not depend on the moisture content and is associated with other polar molecules
which are part of the cellulose. We developed a new method converting experimental frequency depen-dence of the loss angle tangent, measured by the FDSmethod to the reference temperature of 293 K (20°C),using the exponential dependence of the relaxation
time on the temperature, was developed. The activa-tion energy of the relaxation time was determinedbased on the loss angle tangent of moist electrotech-nical pressboard impregnated with insulating oil. Itwas found that the variation in moisture content in the composite cellulose–mineral oil–water nanoparticles do not cause changes in the activation energy of the
relaxation time. The conversion of experimental frequency dependence of the loss angle tangentdetermined by the FDS method to the reference temperature of 293 K (20°C) eliminates the temper-ature dependence in the areas of ultra-low and low
frequencies occurring in the runs made directly on the basis of the measurement results. After calculating the frequency dependence of the loss angle tangent to the
reference temperature, all that remains is its depen-dence on the moisture content
