Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

One of the major issues with natural ester fluid as transformer insulant is encountered due to the oxidation process, which forms a thin gel layer due to polymerization. This latter can hinder the electrical and heat transfer properties. To understand the process, methodical thermal ageing of natural esters was carried out for a 500-hours duration under atmospheric conditions at 160°C. The characteristic variation of fluid-forming gel was investigated by Nuclear Magnetic Resonance (NMR) with the thermal ageing, through which molecular weight degradation and iodine index of thermally aged oil have been estimated for transformer applications. It was observed that the molecular weight and iodine index of thermally aged oil were reduced to 8.31% and 43.016% respectively, after 500 hours of ageing. To further comprehend this, thermogravimetric analysis (TGA) was carried out and heating calorific value (HV) was estimated through bomb calorimetric studies. HV value for 500-hour aged oil and gel was found to be nearly similar. Electrical discharge performance of the oil was estimated through Corona inception voltage (CIV) studies under non-uniform electric field configuration adopting ultra-high frequency sensor (UHF) techniques. Iodine index was found to be in direct correlation with the CIV measurement.