Study on the evaluation method of polymerisation degree based on Raman spectroscopic plot

In order to achieve accurate quantitative evaluation of the ageing state of oil paper insulation, an evaluation method of polymerisation degree (DP) of oil–paper insulation based on Raman spectroscopic plot is presented. Samples covering the full ageing stage of oil–paper insulation were obtained by accelerated thermal ageing experiments. The samples were tested by Raman spectra, and the Raman spectra were converted into Raman spectroscopic plot using Gramian angular field. Feature extraction was performed on the images using local binary pattern (LBP), and 28 feature variables were selected by competitive adaptive reweighted sampling and uninformative variable elimination. Finally, the DP prediction model was constructed by long short-term memory neural network (LSTM). The training accuracy exceeded 90%, and the mean absolute deviation of DP prediction for 45 test samples was only 40.70. A new visual detection method for transformer ageing diagnosis is presented.