Non-invasive monitoring of transformers using the frequency response from controlled transient signals

Abstract

This article presents a novel procedure for applying controlled transient signals analysis with the goal of obtaining the frequency response (FRA) with the transformer in service. For the procedure the method used is IFRA (Impulse Frequency  Response  Analysis)  complemented  with  the  Wavelet  Transform.  IFRA,  has  been  implemented  in  previous  works  to  transform  transient  signals  from  the  time  domain  to  the  frequency  domain  by  means  of  Fast  Fourier Transform (FFT); however, Fourier is not the most suitable tool for this type of analysis since by definition, Fourier is useful for processing stationary signals. Taking that into consideration it was used Wavelet Transforms, given their variable time/frequency resolution, which improved the repeatability of the frequency response curves, as observed in experimental results.The  analysis  developed  was  applied  in  a  single-phase  distribution  transformer  of  7620/240  V,  3  kVA,  to  show  the  viability  of  the  proposed  method,  for  obtaining  the  frequency  response  curve,  which  could  be  used  for  power  transformers in service.