Modified furfural-DP equation with different oil-paper-pressboard mass ratios under oil replacement condition

The furfural analysis is an effective method to evaluate the aging state of transformer cellulose insulation. However, the existing research on the furfural analysis mainly focuses on ‘oil-paper’ system, without considering the oil-paper-pressboard system. In fact, the mass of insulating pressboard occupies a large proportion in the transformer, and there are obvious differences in the mass ratio of oil-paper-pressboard among transformers with different voltage levels, which will affect the effectiveness of furfural analysis. In addition, oil replacement is an oil treatment method to improve the insulation performance of oil, which will lead to the loss of furfural content in oil. In view of this, a series of experiments and studies were carried out to obtain the modified equation between furfural and degree of polymerization (DP) of paper/pressboard insulation with different oil-paper-pressboard mass ratios under oil replacement condition. Firstly, accelerated thermal aging experiment of insulation samples with various oil-paper-pressboard mass ratios was conducted in the lab, and the effect of oil-paper-pressboard mass ratio on furfural was analyzed. Then, the oil replacement experiments were performed, and the oil replacement compensation factor was proposed. Finally, a modified furfural-DP equation was established. This paper attempts to report a method for analyzing the effect of oil-paper-pressboard mass ratio and oil replacement on furfural-DP equation. These findings are expected to improve the application of furfural analysis in field transformers.