Time domain diffusion-driven dielectric response model for investigation of moisture dynamics in transformers insulation

In this paper a time domain diffusion-driven model is presented to investigate the correlation between the distribution of moisture during thermal transients, and the resultant polarization and depolarization current (PDC) measurement, for transformer cellulosic insulation. The oil-impregnated cellulosic insulation is modeled as being multiple layers of paper, with each layer having a different permittivity and conductivity. The non-uniform distribution of moisture occurring during diffusion was taken into consideration. The correlation between moisture concentration and conductivity of the cellulose insulation was investigated. Then, the dielectric response of the cellulose was computed and the dielectric relaxation behavior affected by the moisture dynamics was modelled. The moisture diffusion experiments were conducted on a test transformer to verify the proposed model.