Baza Publikacji Pracowników Politechniki Lubelskiej
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Research on Changes in the Phase Shift Angle and Admittance of the Cellulose–Bio-Oil Composite under the Influence of Increasing Moisture during the Long-Term Operation of Power Transformers
This research was supported by a subsidy from the Ministry of Education and Science (Poland) for the Lublin University of Technology as funds allocated for activities in the scientific disciplines of Automation, Electronics, Electrical Engineering and Space Technologies (grants: FD-20/EE-2/702, FD-20/EE-2/703, FD-20/EE-2/705, and FD-20/EE-2/707).
In this study, the temperature–frequency dependencies of the pressboard–bio-oil–water
nanoparticle composite’s fundamental parameters—phase shift angle and admittance—were ex-
amined using the Frequency Domain Spectroscopy method. Measurements were conducted in a
frequency range of 10−4 Hz to 5 × 103 Hz at temperatures ranging from 293.15 K to 343.15 K, with a
step of 10 K. The temperature stabilization accuracy was less than ±0.05 K. A total of 15 Arrhenius
plots were determined for various phase shift angle values, from which 15 values and the average
activation energy of relaxation time were determined. Similarly, the values of the activation energy of
admittance relaxation time and the activation energy of admittance were determined. It was estab-
lished that all three average values are identical within the bounds of uncertainty. Based on 45 values,
a generalized activation energy was determined, with a value of ∆W ≈ (1.032 ± 0.0196) eV. Using the
generalized activation energy value, the phase shift angle curves determined for all temperatures
were recalculated to a temperature of 293.15 K. It was found that after conversion, all curves perfectly
overlap. A similar operation was carried out for the frequency dependencies of admittance. In this
case, too, the recalculated dependencies perfectly match. This means that the shape of the frequency
dependencies of the phase shift angle and admittance depends solely on the moisture content in the
pressboard–bio-oil–water nanodrop composite. The position of the curves in doubly logarithmic
coordinates depends only on temperature and is determined by the generalized activation energy
Using the generalized activation energy determined in this study will allow for the development
of accurate methods for estimating moisture content in cellulose insulation of power transformers
containing bio-oil. This will contribute to the detection of critical moisture content, which is about
5% by weight, and to the elimination of the ris