Aging characterization of thermally aged transformer paper based on its reflectance

In this contribution, a simple non-destructive characterization of aging degree of oil-paper insulation materials based on the reflectance is proposed. Samples of cellulose Kraft paper having different thicknesses, were thermally aged in a mineral insulating oil and a synthetic ester with a controlled aging history. The degree of polymerization of the non-aged and aged paper samples was measured according to ASTM D4243 to monitor the cellulose degradation. In addition, the samples were optically analyzed to assess changes in paper’s reflectance. The reflectance spectra of the thermally aged paper samples were statistically analyzed using linear, single variable, and multi-variable analyses by considering eight popular variables. This enables correlating the reflectance to the degree of polymerization and identifying a suitable regression model. Appropriate variable interaction has been performed among which two best-fit models with goodness of fit ≥ 0.9 have been identified. The estimation of the cellulose paper’s DP using the proposed models is reported. The experimental results show that the proposed approach can be used in characterizing aging degree of oil-paper insulation and has the potential to be implemented online as an effective monitoring technique.