부산대학교 도서관

The study presented in this paper aims to identify the phenomena leading to the aging of the insulation of in-service high power transformers, in view of adopting optimal solutions to keep them in running. The phenomena analyzed in this paper are largely caused by the inrush current that occurs at the energization of the transformer, which led to the generation of electric arc and also to the appearance of gases dissolved in the transformer oil. The analysis of dissolved gases in oil (DGA) sampled from a 440-MVA in-service transformer was performed, using the Duval Pentagons 1 and 2, which provide additional information that can help identify various types of failures, especially if their nature is different. The results obtained from the DGA analysis led to the identification of thermal faults caused by electric discharges both inside the transformer, and outside it. The technical inspection carried out after the DGA analysis led to the validation of the analysis; there were traces of these electric discharges. Technical solutions have been proposed to avoid overheating of the transformer insulation and the occurrence of electric discharges.