Influence of measurement parameters on FRA characteristics of power transformers

With the increasing average in years of use of transformers, there is an increasing need to ascertain transformer condition. Therefore, it is of vital importance to establish monitoring and diagnostic techniques capable of assessing transformer operating conditions. Frequency response analysis, generally known within the industry as FRA, is one diagnostic technology applied to transformers. The crucial advantage of the FRA method is diagnostic results that can be clearly obtained while bypassing the costly inspection of an untanked transformer after a failure has occurred. However, if FRA characteristics are affected by parameters other than windings or core, fault diagnosis could not be performed with accuracy. In order to investigate the influence of measurement parameters, FRA measurements and simulations were carried out changing the length of the measurement cables, presence of bushings, presence of insulating oil, and tap connection. As a result, it was found that these measurement parameters affect the FRA characteristics.