Fig. 1. Oil-paper insulation accelerated thermal aging test process

Fig. 2. Changes in polymerization degree of insulating paper from 0 to 30 days and classification of aging stages

Fig. 3. Structure diagram of Raman spectroscopy detection platform

Fig. 4. Raman spectrum preprocessing

Fig. 5. Adaboost discriminant model program block diagram

Fig. 6. Aging state diagnosis process of oil-paper insulation Raman spectrum based on local linear embedding

Fig. 7. Relative change of Adaboost discrimination accuracy with number of base classifiers

Fig. 8. Raman spectra of insulating oil at different aging stages

Fig. 9. Raman spectral feature extraction results. (a) PCA feature extraction results; (b) LLE feature extraction results

Fig. 10. Raman spectrum aging degree identification results. (a) PCA feature extraction+Adaboost; (b) LLE feature extraction+Adaboost