Effect of Secondary Drying Impregnation on the Breakdown Characteristics of Oil-Paper

During the production and operation of oil-immersed transformers, oil-paper is often subjected to secondary drying impregnation due to the associated damp conditions. The influence of secondary drying impregnation on the insulation performance of oil-paper is a general concern of equipment manufacturers and operation departments. This study focused on the influence of initial and secondary drying impregnations on the breakdown strength of oil-paper under different temperatures and water content conditions. A comparison analysis between the breakdown strengths after secondary and initial drying impregnations revealed that the percent decrease of the breakdown strength of oil-paper first increase and then decrease with the increase of the water content; moreover, a higher temperature leads to higher peaks in the percent decrease trend. An analysis of variance of the results of orthogonal experiments showed that secondary drying impregnation significantly influences the breakdown strength of oil-paper (significance level = 0.9); additionally, an interaction diagram of secondary drying impregnation, temperature, and water content indicated that these three factors are coupled.