Study of the dielectric response in mineral oil using frequency-domain measurement

Abstract

Debye process and dielectric state of an alcohol in a nonpolar solvent J. Chem. Phys. 134, 044525 (2011); 10.1063/1.3543713 Finite-element modeling method for the study of dielectric relaxation at high frequencies of heterostructures made of multilayered particle J. Appl. Phys. 102, 124107 (2007) Dielectric spectroscopy is a powerful tool to study dipole relaxation, electrical conduction, and structure of molecules. Electrode polarization, as a parasitic effect due to the blocking of charge carriers in the vicinity of an electrode, can make the frequency response at low frequency difficult to understand. Since charge carriers in mineral oil are not only generated from dissociation but also from injection at electrodes, current induced by motion of injected charge carriers should also be taken into consideration. The polarization caused by the injection current has been studied in this paper. When the electric field is not intense, the injection current is proportional to the field and only contributes to the imaginary part of the complex permittivity. A new model has been proposed with this injection current being involved. The frequency responses of three different kinds of mineral oils have been measured and this new polarization model has been used to fit the experimental data. According to the simulation result, the frequency-dependent curves of complex dielectric permittivity calculated from the polarization model could fit the experimental data well. The amount of the injected charge carriers increases with the aging time. This new model enables one to gain a better understanding of electrical conduction in mineral oil. V C 2014 AIP Publishing LLC.

Review of Research Progress on the Electrical Properties and Modification of Mineral Insulating Oils Used in Power Transformers

“…Zhou and co-workers suggested to the characterize charge carriers in mineral insulating oil by using the polarization and depolarization currents, and simulate the frequency response by the calculated insulating oil conductivity [58,59].…”

Quantitative study of electric conduction in mineral oil by time domain and frequency domain measurement

“…Besides, the correlation between the motion of the charge carriers and the polarization and depolarization current has not been well understood. In our previous work, we have found that the AC conductivity increases with ageing period, whilst the frequency dependent permittivity does not change much within a frequency range from 100 to 0.01 Hz [14]. With Frood's assumption that there might be high mobility and low density charge carriers in dielectric liquid, this frequency domain dielectric behavior can be explained [15].…”

“…Thus, the depolarization current mainly relies on the motion of the ionic charge carriers. As the space charge polarization theory [14], which is based on this assumption, indicates that the total conductivity is only partially contributed by the motion of the ions, the conductivity calculated from time domain experimental results should also be lower than the experimental value. In this chapter, an analytical expression to estimate the conductivity from the depolarization current will be proposed.…”

“…In our previous work, a polarization theory involving the motion of the charge carriers that have low density and high mobility has been proposed. If these high mobility charge carriers do exist, the total conduction should contain two parts: the ionic conduction induced from the motion of the ionic charge carriers and the conduction that is induced from those high mobility charge carriers [14]. It has been reported that the ratio of the conductivity contributed by the motion of the ionic charge carriers over the total conductivity decreases with the ageing period [14].…”

“…With Frood's assumption that there might be high mobility and low density charge carriers in dielectric liquid, this frequency domain dielectric behavior can be explained [15]. Later, a space charge polarization theory based on this assumption has been developed [14]. As the mechanism of the electric conduction in mineral oil must be consistent under both AC and DC field, the polarization theory that was developed in frequency domain should also be valid under DC field.…”