Analysis of Variation in Nonlinear Impedance Characteristics of Damp Oil-Paper Insulation

Oil–paper insulation in transformers plays a crucial role in ensuring the safe and stable operation of power equipment. When oil-paper insulation becomes damp, its response current waveform becomes distorted and generates a large number of harmonic components, and this nonlinear impedance characteristic significantly affects the evaluation of insulation performance. Based on this nonlinear dielectric characteristic, this paper simulates and analyzes the deformation process of water droplet adsorbed by fiber in oil-paper insulation under an AC electric field. It is found that under the action of the electric field, the water droplet gradually changes from its initial circular shape to an elliptical shape, and its current density waveform becomes distorted. The degree of distortion increases with the increase in electric field strength and the decrease in frequency. The results indicate that the deformation process of water droplet within oil-paper insulation under an electric field after moisture absorption is the primary cause of the nonlinear impedance characteristics that influence its dielectric response.