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

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.

Automated summary

Ionic transport process plays an important role in oil-paper insulation by affecting the oil flow electrification at the oil-paper interface. The dynamics and mechanisms of this process are still unclear at the molecular level. Molecular Dynamics study was conducted to investigate the transport behavior of impurity ions in different oil-paper insulation models under various external electric fields. The results show that ionic mobility and its response to electric fields are higher in weaker electrostatic models, with mineral oil exhibiting the highest ionic mobility. Understanding the dynamics of ion transport in oil-paper insulation is crucial for improving the insulation properties of oil-impregnated power transformers.