Frequency response analysis- condition assessment of power transformers using mathematical and statistical criteria

Today, frequency response analysis (FRA) is increasingly being used to evaluate the physical and insulating structure of power transformers. This technique is based on comparisons between transformer frequency responses and judgment with respect to their differences. However, graphical analysis to assess the transformer status requires the trained experts to interpret test results. In this paper, four different statistical and mathematical criteria are presented and evaluated for comparing the results of FRA measurements. The mathematical definition of these criteria is given and applied to a number of healthy and faulty transformers as suitable case studies. The sensitivity and strength of criteria in each case is evaluated. The results clearly show that a number of presented criteria are very useful and reliable in most cases especially when the experts are not present on the scene.