Power transformers are one of the most important components of the electrical power networks. A wide range of mechanical and electrical stresses in addition to the aging could cause failures in these apparatuses. As a result, evaluating the condition of the transformers during their lifetime is crucial to the power network reliability and service continuity. A large number of different fault diagnosis techniques are introduced for this purpose. Frequency Response Analysis (FRA) is sensitive to the great number of electrical or mechanical changes in the transformers that could occur during the manufacturing, transportation, installation, maintenance or operation of the device. Therefore, FRA is considered among the powerful methods of transformers' condition assessment. This paper explains the frequency response analysis of transformers method, its application and test procedure as well as providing a comprehensive review of the researches and attempts that are done on different aspects of this field for enhancing quality and repeatability of the test and the interpretation of the results

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