Resumo

MARTINS, M. Augusta G.. Será o óleo vegetal um possível substituto do óleo mineral para transformadores?. C.Tecn. Mat. [online]. 2008, vol.20, n.3-4, pp.15-20. ISSN 0870-8312.

Uses of natural esters (vegetable oil) as insulating fluid have been reported, recently. This fluid has high biodegradability and high flash point what for safety reasons is attracting some attention in electrical industry. As insulating fluid is used for cooling, insulation and protection of the solid insulating paper, it is important to have some knowledge about the paper ageing in such fluid. It is reported here, a study of paper ageing in vegetable oil, under laboratory experimental condition, at a dynamic temperature increase in the range 70ºC-190°C. The experiment was conducted in sealed glass reaction vessels, for both oil (blank) and oil/paper heated inside an oven. The paper used for this study is kraft paper. Moisture formation at different temperatures, in oil and in oil/paper system, is reported together with generated gases. Changes of degree of polymerization of paper and formation of furanic compounds with changes of temperature are also reported. Paper degradation in vegetable oil is compared with paper degradation in mineral oil. Both degradation rates are similar, at the same temperature. At temperatures under 130 ºC the ageing of paper in vegetable oil is only a little bit quicker, than in mineral oil.  However, for temperatures higher than 130 ºC, the rate of paper degradation in vegetable oil is even a little bit lower than in mineral oil. Finally, are also presented the degradation models, developed to calculate the average viscosimetric polymerization degree of paper, based on 2FAL concentration dissolved in insulating oil, in both cases.

Palavras-chave : Vegetable insulating oil; Thermal degradation; Transformer; Kraft paper; Biotemp; Polymerization degree; DP_v; Furanic compounds; 2-furfuraldheide; 2FAL.

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