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Ciência & Tecnologia dos Materiais

versão impressa ISSN 0870-8312

Resumo

MARTINS, Maria Augusta G.. Envelhecimento térmico do papel isolante de transformadores. Investigação experimental. Modelos de degradação.. C.Tecn. Mat. [online]. 2010, vol.22, n.1-2, pp.77-86. ISSN 0870-8312.

The processes involved in the thermal ageing of insulating paper used for electrical power transformers, are not very well known, due to the role played by a great number of parameters and their difficult control. To get information for characterization of those processes, accelerated thermal ageing experiments of cellulosic insulating paper, (Kraft paper) immersed in insulating mineral oil inhibited (0,3 % DBPC - Di-tert-butyl-para-cresol - Oxidation inhibitor) and containing 25 mg of BTA /kg oil (Benzotriazol - BTA - Copper passivator) were undertaken in sealed glass ampoules, heated in an oven, at temperatures in the range 70 ºC - 180 ºC. The monitoring of paper degradation was done by the analysis of some gases dissolved in oil such as: hydrogen, hydrocarbons, oxygen, carbon monoxide and carbon dioxide and liquids like: water and furanic compounds and also by the determination of the degree of polymerization of the paper samples, (DP), besides the analysis of furanic compounds absorbed in the paper. New mathematical relationships of furfuraldehyde concentration in oil, versus the corresponding DP of paper, were established in the above mentioned experiments calculated for oil/paper ratios of core and shell transformers and afterwards compared to degradation models, developed by other researchers. Finally, the importance and advantages of these degradation models used for assessment of the useful remaining life of insulating paper of transformers, and the limitations of its application to the assessment of the useful remaining life of transformers are also highlighted here.

Palavras-chave : Thermal ageing; Kraft paper; Hydrolysis; Pyrolysis; Thermal oxidation; Cellulosic insulation; Furanic compounds; Degree of polymerization; DGA; Degradation models.

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