Interpretation of Turn-to-Turn Insulation Fault by Dissolved Gas Analysis

The purpose of dissolved gas analysis (DGA) in utilities is to help detect the presence of abnormality within transformer. When faults occur in transformers, transformer engineers need to determine the location and risk of the faults. Ultimately, they have to decide, based on DGA, whether to continue operating or not, perform internal inspection, or dispose the transformer. In this study, the fault and failure types in the transformer are suggested to determine the location and risk of the faults. In particular, turn-to-turn insulation faults are classified as degradation and breakdown. These faults are difficult to identify during internal inspection, and have a high possibility of failure. Urgent decision and action are thus required to avoid failure. In degradation of turn-to-turn insulation faults, failures may occur by generating thermal gases in paper during a long period of time. In breakdown of turn-to-turn insulation faults, thermal gases are not generated in paper, and failures are rather due to sudden breakdown of insulation. This study also presents a typical example of a turn-to-turn insulation fault. This example shows the progress of the fault from thermal to discharge, which is common phenomena in winding fault. Based on the findings of this work, transformer engineers can determine by DGA if transformers can be operated with or without internal inspection, or disposed when the fault has not been identified during internal inspection.