Experience Gained from Using the Frequency Response Analysis in Performing Diagnostic Surveys of 10–500 kV Power Transformers

The article discusses the application of the frequency response analysis for diagnosing various defects in the cores and windings of 10-500 kV power transformers. A schematic approach to defining the dynamic zones of frequency responses is proposed. The optimal measurement configurations are determined. A method for calculating the basic characteristics proceeding from the data of measuring the frequency responses of same-type transformers is developed. Specific examples of determining various defects by analyzing the frequency responses of 10-500 kV transformers are given. The scope of defects diagnosed includes core deformation, radial winding deformation, the presence of short-circuited turns in the winding, and winding displacement from the vertical axis. The obtained results have been confirmed by visual inspection of the active part, as well as by other types of tests and measurements. Various statistical coefficients used for evaluating defects in the transformer active part are compared. Tentative permissible values of the standard deviation coefficient to quantify the severity of defects grown in transformer cores and windings have been proposed.