Modelling and measurement of field dependent resistivity of transformer oil

Abstract

This article studies the apparent resistivity of mineral oil as a function of electric DC stress using theoretical and experimental methods for three different oils. The experimental measurement of the apparent resistivity is done using a cell with two bare Rogowski like electrodes separated by a 2mm gap. The dc current is measured after one hour and the stress is varied in steps. For low DC stress the apparent resistivity rises with increasing voltage, leveling off and dropping slightly for higher voltages. The resistivity is modeled using the ion drift model with equilibrium resistivity measured using dielectric response as input. The charge dynamics and the corresponding resistivity is simulated and the results compared with the measured values. The main features seen in the measurements are captured in the simulation and there is a good overall agreement between the theoretical data and the experimental values.

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

“…Later, Macdonald pointed out that Jaffé's assumption that the density of the charge carriers did not change much during the polarization and depolarization process was only valid under a voltage of 0.2 V, which was much lower than the voltage applied in Jaffé's experiment [10]. The classic ionic drift and diffusion model has been widely employed in the study of the electric conduction in mineral oil [11][12][13]. Gafvert et al have studied the field distortion between two parallel electrodes under DC field [12].…”

“…Gafvert et al have studied the field distortion between two parallel electrodes under DC field [12]. The ionic mobility has been estimated using the ionic drift and diffusion model by many researchers [11][12][13]. Recently, Lavesson et al proposed a computer based method to simulate the field dependence of electric conduction and they found that the simulation results had a good agreement with the experimental results [13].…”

“…The ionic mobility has been estimated using the ionic drift and diffusion model by many researchers [11][12][13]. Recently, Lavesson et al proposed a computer based method to simulate the field dependence of electric conduction and they found that the simulation results had a good agreement with the experimental results [13]. However, how to evaluate the high field resistivity of mineral oil is still under debate and this topic has been discussed in CIGRE Study Committee A2: joint working group JWG A2/D1.41 "Transformer insulation -oil conductivity".…”

Simulation of the integral electric current characteristics of unsteady-state current passage through liquid dielectrics

“…Besides, the method was supplemented with the technique for calculation of the total current passing through the external electrical circuit in the unsteady-state regime [6]. Thus, whereas a number of computer investigations of high-voltage current passage processes deal with hydrostatic case (e.g., [2,7,8]), the present work features joint computation of the electrohydrodynamic flow and the integral electric-current characteristic, which, in turn, allows one to advance in the interpretation of the experimental data and verify existing theoretical models.…”