Frequency response analysis as a technique for moisture diagnostics of power transformers

FRA is used to determine the mechanical and electrical integrity of the core and the windings of power transformers. It can be used to detect core movement, winding movement, open circuits, short circuits and problems related to core ground. Various practical case studies demonstrate the effectiveness of this technique. This paper will demonstrate the effect of change in moisture content on the resonance frequencies of the FRA signatures. An attempt is made to set an approximate relation between the resonance frequency and the percentage moisture content. Therefore, the amount of moisture content can be approximated by identifying the shift in the resonance frequency occurring along the sweep relative to the reference. Practical examples of the application are presented.