Application of dielectric response techniques for the condition assessment of power transformers

In recent years, new diagnosis and monitoring techniques using the dielectric response have been developed for insulation condition assessment. Their sensitivities to aging and their potential to predict residual live is still to demonstrate. To respond to these issues, we have started an investigation and looked at the potential of two electrical methods to be sensitive to aging and how their signatures can be related to the transformer age and condition. This study covers the evaluation of the dissipation factor (tan δ) versus frequency and the polarization-depolarization current (PDC) measurements for their sensitivity to aging of the insulation. This evaluation is performed using model transformers with various moisture content and aging degrees. Insulation has been assessed at every stage of aging with oil and paper analysis. The two dielectric methods have been measured at every stage of aging. The results and the correlation between the dielectric measurements and the paper and oil aging parameters as well as the insulation moisture content are discussed.