Semiconductor Physics, Quantum Electronics & Optoelectronics, 29 (3), P. 367-373 (2026).
DOI: https://doi.org/10.15407/spqeo29.03.367

Temperature dependences of parameters characterizing dielectric properties of transformer oil with magnetic liquid impurities

O.V. Kovalchuk^1,2*, Y.A. Garbovskiy³, T.M. Kovalchuk⁴, L.V. Volokh⁴, I.V. Oleinikova⁴, K.V. Avdonin⁵, K. Paulovičová ⁶, L. Tomčo⁷, P. Kopčanský⁶

¹Kyiv National University of Technologies and Design, 2, Nemirovich-Danchenko Street, 01011 Kyiv, Ukraine
²Institute of Physics, NAS of Ukraine, 46 Nauky Avenue, 03028 Kyiv, Ukraine
³Department of Physics and Engineering Physics, Central Connecticut State University,
1615 Stanley Street, New Britain, CT 06050 USA
⁴V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine, 41 Nauky Avenue, 03028 Kyiv, Ukraine
⁵Military Institute of Telecommunication and Information Technologies named after the Heroes of Kruty,
45/1, Knyaziv Ostrozkykh Street, 01011 Kyiv, Ukraine
⁶Institute of Experimental Physics, Slovak Academy of Sciences, 47 Watsonova Street, 04001 Košice, Slovakia
⁷Department of Aviation Technical Training, Faculty of Aeronautics, Technical University of Košice,
Rampová 7, 04001 Košice, Slovakia
^*Corresponding author e-mail: akoval@knutd.com.ua

Abstract. The dielectric properties of pure transformer oil and transformer oil with a magnetic liquid impurity with a concentration of 4.2 vol.% have been investigated in the frequency range of 6 to 7·10⁵ Hz and at the temperatures of 308 to 423 K. The dielectric permittivity of the transformer oil has been shown to increase almost linearly with temperature. The dielectric permittivity of the transformer oil with the magnetic liquid impurity has exceeded the dielectric permittivity of the transformer oil without impurities and depended nonlinearly on temperature. The electrical conductivity of the transformer oil without impurities in the entire frequency range and the transformer oil with the magnetic liquid impurity at the frequencies f > 3·10³ Hz at a specific temperature have been shown not to depend on the frequency. These values of the electrical conductivity reflect the bulk properties of the liquid. The temperature dependence of the electrical conductivity has been shown to correspond to the Arrhenius law. It has been found out that the activation energy of the temperature dependence of the electrical conductivity of the pure transformer oil is 0.27 eV, and 0.22 eV at presence of the magnetic impurity. The dispersion of the values of the real and imaginary components of the complex dielectric constant of the transformer oil with the magnetic liquid impurity corresponds to the Cole–Cole dispersion. Based on the analysis of the Cole–Cole diagrams, the values of the relaxation time τ, the thickness of the near-electrode region W, and the parameter characterizing dispersion of the relaxation times α have been found for each of the sample temperatures. The value of τ has been shown to decrease with temperature, the value of W increases at increasing the temperature, and the value of α equals as 0.06 and has no temperature dependence.

Keywords: dielectric permittivity, electrical conductivity, relaxation time, transformer oil, magnetic liquid impurities.