A Two-Step Modification Method for Estimating the Aging Status of Insulation Paper After Oil-Replacement Based on the Methanol

Replace aged oil (RAO) can retard the aging development of transformer insulation by regularly filtering out the harmful substances in oil; however, the RAO itself may affect the estimation accuracy of the aging status of paper insulation based on chemical characteristic marker methods, such as carbon oxides, furfural, and methanol (MeOH). In this article, accelerating thermal aging experiments are carried out, and the influence of RAO on MeOH concentration in insulating oil and the estimation degree of polymerization (DP) of paper insulation is investigated. The results indicate that the current estimation methods are unsuitable for RAO based on the MeOH in oil. Furthermore, the MeOH correction factor (CF) and DP CF are established as power-series expansion, and a two-step modification method that considers both variations of MeOH in oil and DP of paper insulation is proposed for modifying the estimation errors by RAO. Eventually, the verification experiment is carried out to verify the estimation accuracy of the proposed method, and the results indicate that the range of average relative estimation errors is reduced to 1.8%~3.9%. The accuracy of aging estimation is improved and the proposed method has good applicability.