Electrical conductivity measurement and determination of ion mobility in insulating oil

Abstract

The insulation system of power transformers is a key topic which has to be taken into account in order to achieve an optimized design and safe longterm operation. The design of feasible insulation for high voltage direct current transformers requires the understanding of field distributions in insulating materials in both AC and DC operation because the transient stresses are dependent on both conductivities and permittivities and geometry. The steady state DC field stresses are determined by conductivity of insulating material which is normally a combination of oil and paper. Therefore knowledge about the conductivity of the oil is of great importance for design and safe operation in DC case. Moreover the space and surface charges will occur in field space and also will influence the electric field. If such charges are present in a noteworthy amount, models depending on material properties only will probably be an approximation. The conductivity of insulating material is dependent on several parameters, e.g. time, temperature and electrical field strength and the geometry of the arrangement. In this contribution, a new measuring cell with plate type electrodes is presented for analysis of oil conductivity. The measurement accuracy of the set-up is investigated both analytically and experimentally. Consequently, measurements are performed for investigating the time behavior of conductivity. The results show that the determination of ion mobility using polarity reversal test represents to a suitable approach to investigate the transit times more precisely.

Dynamics of an impurity ion transport in oil‐paper insulation under various electric fields

“…Even so, we must admit that the ionic mobility calculated by molecular simulation cannot be quantitatively compared with the experiment. For example, the ionic mobility in mineral oil measured from the experiment is about 1 � 10 −9 m 2 /V⋅s [61,[63][64][65][66], which is one or two orders of magnitude less than the calculated value in this paper. This deviation between simulations and experiments can be attributed to three main reasons.…”

“…On the other hand, classical MD requires a stronger electric field to overcome interactions between ions and polymers to calculate ionic mobility (with E over 0.1 � 10 −1 V/Å in our case). While in the experiment, the reversal polarity method is considered to be a common and overriding method in investigating the intrinsic ionic mobility in oil-paper insulation, with a relatively low electric field ranging from 0.1 � 10 −5 V/Å to 0.1 � 10 −3 V/Å to avoid the effects of charge injection from the electrode or generation of new ions through chemical dissociation induced by high electric fields [61,[64][65][66]. As a final point, the ionic transport model in actual mineral oil may be more complex.…”

Thermal Aging-Based Degradation Parameters Determination for Grid-Aged Oil Paper Insulation

“…Figs. 8-10 are plotted with one sample every 2 s. In OIP samples, the conductivity of insulating oil is exponentially proportional to temperature [11]…”

“…There has been significant research on polarization and depolarization current (PDC) measurement [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13] and frequency dielectric spectroscopy (FDS), including the influence of aging and moisture on oil-impregnated paper [14], [15], [16], [17], [18], [19]. But a majority of research has been based on oilpaper pressboards used in transformers or artificial oil impregnation of kraft paper.…”