Interpretation of Inter-Turn Fault in Transformer Winding Using Turns Ratio Test and Frequency Response Analysis

The transformer is critical equipment in electrical power systems as it is continuously exposed to various failures. Inter-turns fault in the transformer reduces the turns of the winding, thus it can be detected using a Transformer-Turns-Ratio (TTR) test. On the other hand, the Frequency Response Analysis (FRA) method is used for assessing the mechanical condition of the transformer winding and core. In this paper, the TTR, and FRA methods are proposed to detect the inter-turns fault in the transformer winding. The winding inter-turn fault was investigated using FRA inductive inter-winding measurement and compared with the TTR test. Findings from the statistical analysis showed that FRA inductive inter-winding can detect the inter-turn fault. Finally, acceptance limits for the absolute sum of logarithmic error and standard deviation were proposed. The limits were established based on TTR’s acceptance limit from the IEEE standard. This finding proves that the FRA test can be used to complement the result in the conventional TTR test.