Frequency Response Analysis (FRA) in power transformers: An approach to locate inter-disk SC fault

One of the most powerful and accurate tool for winding deformation detection in power transformers is Frequency Response Analysis (FRA). But the interpretation of FRA plots still needs a higher level of expertise to identify and quantify faults as there is no FRA interpretation code widely accepted yet. Currently only magnitude plot is used for detection of the fault using FRA. This work presents an approach of FRA signature interpretation for identifying the location of inter-disk short circuit fault in transformers by using polar plot along with bode plot. Inter-disk short circuit fault across HV side was simulated and bode plot and polar plot of the transfer function was studied. Two parameters, Area parameter and magnitude corresponding to the point at last resonance where the phase of transfer function becomes 180° for the first time were identified. An equation was formed with which, the location of the fault can be identified using area parameter obtained.