Influence factors on FRA waveforms

With the increasing average use years of transformers there is an increasing need to know the transformer condition. Therefore, appropriate monitoring and maintenance become important as the oil-immersed transformer ages. Generally DGA (Dissolved Gas Analysis) is effective for the on-line diagnosis, and if abnormality is detected, FRA (Frequency Response Analysis) is effective for the off-line diagnosis to localize the failed part. FRA is one of the diagnostic technology of a transformer. The crucial advantage of FRA method is obviously given the diagnosis results through bypassing the costly inspection of the untanked transformer after the occurring failures. FRA measurements aim to diagnose damage to windings or cores of transformers from the outside by detecting a few differences in the waveforms that show frequency response characteristics. Should these differences be affected by external factors, fault diagnosis could not be performed with accuracy. FRA diagnosis detects the slight change of waveforms, where external factors may influence the results. Here, we discuss the influence factors on FRA waveforms.