evaluation of online techniques utilized for extracting the transformer transfer function

Power transformers are of vital importance in power delivery and, therefore, different diagnostic techniques have been proposed for them. the frequency response analysis (fra) is an effective method that detects mechanical changes in transformer windings by extracting the transfer function. there are various approaches to obtaining the transfer function online, which is known as the online fra technique. this paper compares these different mathematical approaches for obtaining the transfer function of a transformer. a comparison is carried out by defining an appropriate model for the transformer and applying these mathematical methods to it. the effect of other power network equipment on the transformer transfer function is also studied in this paper. the results of this contribution determine proper methods for the online fra technique, which can be used in the transformer monitoring applications.