Investigation of Acetylene Gas and Internal Hotspot in the Low Voltage Bushing of Power Transformer #1 Telukjambe Substation

Power transformer is one of the most important pieces of equipment in the electric power system, because it supplies electrical energy to residential, business, and industrial consumers. Transformer #1 Telukjambe Substation has a unique case, where the DGA test results shows that there was an appearance of C2H2 with condition 3 but not followed by an increased value of other gaseous compounds. Internal hot spot was found on the secondary bushing of S and T phase, while R phase was normal. Shutdown measurements were carried out and the results shows that based on the SFRA test, there were suspected distortions at low frequency in various test modes. There was a deviation value of winding resistance at secondary winding between phases of more than 2%. In the investigation process, burnt traces were found on the tap selector winding connection and mechanical movement of OLTC was not perfect, the appearance of C2H2 was suspected from it. Carbon traces also were found on the secondary bushing rod connection. After repair and oil purification, SFRA test results became normal and deviation value of secondary winding resistance between phases became less than 3%, and C2H2 gas in Transformer #1 became normal.