This article presents results on the DC conductivity of moist pressboard impregnated with insulating oil and its dependence on the moisture and temperature of the samples. The transfer of charges was found to take place because of electron hopping between potential wells produced by water nanodrops. The average dimension of the nanodrops was around 2.32 nm, forming approximately 220 water molecules.

The paper presents results of investigations of the effect of moisture content and temperature on DC conductivity of the impregnated pressboard. It has been found that the conductivity of the impregnated pressboard is a function of activation energy, moisture content and temperature. It has been found that moisture content ranging from 1.4% to 6.4% do not cause any changes in the conductivity activation energy whose value is ΔW _av = (0.853±0.071) eV. On the other hand water content strongly influences the value of DC conductivity. It has been also found that the conductivity is determined by electron hopping between the closest located potential wells formed by water molecules in the oil-impregnated cellulose structure. For the experimentally obtained dependences of conductivity vs. moisture content and temperature theoretical ones have been determined to describe the experimental results. Based on the research results, a localization radius of the water molecule valence electron that coincides with the O ^2- ion radius has been determined. The obtained results concerning DC conductivity vs. moisture level and temperature dependence of an electric insulation pressboard can make a basis for the identification of the amount of moisture accumulated in solid elements of a power transformer paper-oil insulation.

The paper presents research results of testing AC conductivity in a moist oilimpregnated electric insulation pressboard, depending on the moisture content level and temperature of the samples. A new method has been elaborated for converting experimentally obtained dependences from frequency-domain spectroscopy (FDS) to the reference temperature of 293 K (20 /dpl deg/C). Activation energy values have been determined for the conduction and relaxation time. It has been found the conductivity is realized by electron tunnelling between potential well formed by water molecules contained in the structure of moist cellulose.

The paper presents results of testing permittivity of an oil-impregnated electric pressboard containing water nanoparticles depending on AC frequency, moisture content level and the temperature of samples. A new method has been developed for converting experimentally obtained frequency dependences of permittivity determined with the frequency-domain spectroscopy (FDS) to the reference temperature of 293 K (20 °C) using exponential dependence of the relaxation time versus temperature. Activation energy of the permittivity relaxation time has been determined for a moist oil-impregnated electric insulation pressboard. It has been established that variations of the moisture content level in a composite of cellulose, mineral oil, and water nanoparticles do not cause any changes in the relaxation time activation energy value, neither in energy states of electrons in potential wells nor in the structure of water nanoparticles. It has been also found that the conversion of experimentally obtained permittivity versus frequency dependences determined with the FDS method to the reference temperature of 293 K (20 °C) eliminates temperature dependences that occur in characteristics based directly on measurement results. Once the relative permittivity is converted to the reference temperature it is only its dependence on the moisture content level that remains.

In this work, the temperature and frequency dependences of the real part of the admittance [σ(f, T)] of annealed nanocomposite films containing Co₄₅ Fe₄₅Zr₁₀-based nanoparticles covered with native oxides and embedded in a doped PbZrTiO₃ ferroelectric matrix were studied. The nanocomposites studied were deposited by ion sputtering a complex target in a mixed Ar/O₂ atmosphere followed by a 15-min annealing process (with steps of 25 K) in air in the temperature range of 398 K ≤ T _a ≤ 573 K. The σ(f, T) of the annealed samples was measured in the temperature range of 77 K < T _p < 373 K at frequencies of 50 Hz < f < 1 MHz. The observed σ(f, T) dependences confirmed that the annealed samples displayed the effects of negative capacitance over the whole frequency and temperature ranges studied because of the pronounced oxidation of the nanoparticles. The σ(f, T) dependences obtained are described using an earlier-developed AC hopping conductance model. Comparisons between experimental and simulation results allow the model parameters to be estimated, such as the activation energies of the hopping conductance and the lifetimes of the electrons in the nanoparticles.