Recognition of Mid-Temperature Overheating in High-Voltage Power Transformers by Dissolved Gas Analysis

The results of gas content analysis for 359 highvoltage power transformers with mid-temperature overheating are presented. The values of gas percentage and gas ratios were obtained, and the nomograms of defects corresponding to overheating at temperatures of 300-500°C and 500-700°C were constructed, which allows increasing the recognition reliability of these defects. Based on the analysis of the dynamics of changes in the gas content during the development of the defect, demonstrated by nomograms, it was found that mid-temperature overheating can pose a significant risk for transformers due to the possibility of escalation into more dangerous defects. A comparative analysis of the recognition reliability of mid-temperature overheating, using the best known standards and methods, showed that the most reliable detection is achieved by the gas ratios specified in the IEC standard.