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

Abstract

The ionic transport process is an important counterpart to charge transport in oil‐paper insulation, and it significantly impacts oil flow electrification at the oil‐paper interface. Despite this, the dynamics of this phenomenon and the underlying mechanisms remain unclear, particularly at the molecular level. To understand this fundamental aspect, we conduct Molecular Dynamics study on the transport behaviour of an impurity ion in different oil‐paper insulation models under various external electric fields. Different influence factors, such as external electric fields, temperatures, and local structural characteristics, are investigated in relation to the corresponding ionic mobility in different polymer models. According to the simulations, ionic mobility and its response to electric fields are higher in weaker electrostatic models. As a result, mineral oil exhibits the highest ionic mobility and the most substantial enhancement of ionic mobility by external electric fields, followed by vegetable oil, oil‐paper blends, and insulating paper. This significant deviation in ionic mobility between oil and paper leads to the formation of an electric double layer near the oil‐paper interface. The underlying physical mechanisms of different ionic mobility and its response to the electric field in different polymer models could be explained by the different polymer structural influences in terms of interaction energy and coordination numbers in a static manner, as well as by the interactions between the impurity ion and its surrounding atoms in terms of lifetime correlation functions and velocity autocorrelation functions in a dynamic manner. In addition, the influence of temperature on ionic mobility in mineral and vegetable oil is examined, and their activation energies are calculated. Advancing in the fundamental understanding of the dynamics of the ion transport process in oil‐paper insulation is vital to improving their insulating properties for oil‐impregnated power transformers.

A first-principles study of the formation and regulation of the electric double layers at Cu (0 0 1)/mineral oil interfaces

“…As another alternative, it is possible to adjust the potential structure of the EDL on the liquid side by introducing chemically active atoms, such as Na or F atoms at the interface, and then an EDL structure (Helmholtz layer) is directly introduced into the molecular model [14,15]. By increasing or decreasing the number of positive or negative ions in the electrolyte, an EDL can also be formed at the interface without the addition of additional atoms [18,25]. Additionally, polaronic charge transfer states can be generated using the occupation matrix control method, and then the amount of charge transfer at the interface can be modified accordingly [26].…”