Insulation resistance of power transformers — method for optimized analysis

This paper proposes a method for evaluating and classifying transformers, using equations to obtain scores and ratings for insulation resistance tests as a function of the age of these devices, resulting in recommendations to support decision-making. Analyses were made of test results of power transformers of 1 MVA to 50 MVA, wrapped in insulation Kraft paper and immersed in insulating mineral oil, with nominal voltages of 13.8 kV to 230 kV, ranging from 1 to 51 years old, whose ratings varied from "A" (excellent) to "E" (very poor). The methodology was developed using computational methods of equation optimization involving the hill-climbing algorithm associated with the 1/5th success rule. It was concluded that the combined use of maintenance engineering criteria and computational optimization techniques resulted in an efficient diagnostic method for these devices.