Modelling the low-frequency dielectric response test of insulation oil

The frequency domain dielectric response method has been one of the most effective approaches for condition assessment of an electrical insulation system. The low-frequency part is more effective for diagnosing the moisture content and aging status of oil-paper insulation. To facilitate the study of the low-frequency dielectric spectrum of oil-paper insulation, a model applicable to the low-frequency dielectric response of insulation oil is proposed in this study, which is based on the ionic motion of insulation oil. The creation of charge carriers under field test conditions mainly derives from the dissociation of ionic pairs. During testing, ionic motion of insulation oil is jointly affected by thermal diffusion and the electric field; moreover, dissociation and recombination of negative and positive ions also occur. Therefore, the above factors were all considered in the modelling process. The applicability of the model is verified against measured results. For further interpreting the proposed model, the characteristics of the ionic concentration distribution, the relation between ionic distribution and dielectric properties, and the application of the proposed model are analysed.