Static dielectric constant and dielectric loss of cellulose insulation: Molecular dynamics simulations

Abstract

Reducing the dielectric constant and loss of cellulose insulation can make the electric field distribution uniform in oil-paper insulation systems and decrease the heat generation in dielectric materials, thus ensuring a reliable transformer operation. To guide the experimental design from the molecular level, the fluctuation method was introduced into the molecular dynamics simulation to evaluate the static permittivity of cellulose insulation, εs. The correlation between the dynamics parameter mean square displacement (MSD) and dielectric loss induced by orientational polarization, was investigated. The simulation results and experimental values of five types of cellulose insulation were compared to verify the rationality of the proposed method. The results indicated that the simulation values of εs for five models were agreed well with the experimental values in terms of both the magnitude and the variation trend. The simulation time and permittivity of the surrounding medium εRF are two key parameters, which determine the accuracy of the simulation results of εs. Considering the convergence, 15 ns was chosen as the lower limit of simulation time. The reaction field approximation was adopted to calculate the dipole-dipole interaction instead of true interaction, that is, εRF→∞. The MSD results reproduced the experimental trend in dielectric loss, indicating that the method can qualitatively predict the dielectric loss of cellulose insulation. Hence, these methods are sufficient to guide design experiments and provide a route to understand the mechanism of the change in dielectric properties at the molecular level.