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The applicability of using 2-furfural (2-FAL) and methanol as aging markers for synthetic ester impregnated paper insulation was investigated through laboratory aging experiments at temperatures of 80, 100 and 120 ?C. Methanol in the synthetic ester increased linearly with paper aging until degree of polymerisation (DP) reached 400. During this period concentration of methanol in oil was higher than that of 2-FAL, which proved the concept of using methanol to indicate early paper aging in the synthetic ester. However, the rate of methanol increase against the reduction of DP in the synthetic ester was about three times higher than that seen in mineral oil. This is due to a difference in the partitioning of the marker between oil and paper. Since the synthetic ester is more polar than the mineral oil, it attracted more methanol molecules from the paper, resulting in a higher concentration of methanol in oil for the same reduction of DP. In addition, a reduction in methanol was observed at the later stage of paper aging at 120 ?C. This could be due to either a change in the partitioning between oil and paper, or an esterification reaction which consumes methanol in the system. [ABSTRACT FROM PUBLISHER]

This paper is aimed at the study of aging behavior of cellulosic materials in different dielectric liquids under air and nitrogen atmospheres. Paper for copper conductor and high density transformer board were aged at 130°C up to 1128 h in sealed vessels in presence of mineral oil (MO), natural ester (VO) and synthetic ester (SE). The influence of thermal aging on cellulose and oil characteristics are investigated and compared. It's observed that the paper degradation is associated with the generation of CO2 and CO gases. Whatever the type of oil, this generation is more important with vessel under air atmosphere than that under nitrogen gap indicating a protective effect of nitrogen. In mineral oil, the degree of polymerization (DPv) reaches the end of life criteria at around 200 whereas it remains around 400 with ester oils. This is mainly due to the higher water solubility of esters compared to mineral oil. The measured degree of polymerization in MO is comparable to that calculated through 2-FAL (Furanic compounds) content using Vuarchex equation whereas for esters oil, there is no agreement between the measured and calculated DPv through 2-FAL content. This can constitute a limitation in the use of 2-FAL for the diagnosis of ester-filled transformers. Overall, the insulation cellulose/oil behavior seems better under nitrogen atmosphere. [ABSTRACT FROM PUBLISHER]

Dielectric response is a non-invasive diagnostic method with a potential to give information about the status of the solid insulation in a power transformer. To investigate what conditions the method can and cannot reveal, frequency domain spectroscopy has been applied to oil-impregnated paper and pressboard with and without moisture and/or acids added, and to paper at various stages of aging. Water and carboxylic acids are important aging indicators. It is found that moisture is clearly detectable. Also low molecular weight carboxylic acids will affect the dielectric response in a way similar to moisture, but high concentrations are needed for a contribution comparable to that of moisture. It is difficult to tell moisture and acids apart from the responses obtained. High molecular weight carboxylic acids make little or no contribution to the dielectric response of the solid insulation in a paper/pressboard — oil system. It was also observed that keeping paper or pressboard at elevated temperatures had a conditioning effect on the response. [ABSTRACT FROM AUTHOR]