Effect of Different Connection Schemes, Terminating Resistors and Measurement Impedances on the Sensitivity of the FRA Method

Frequency-response analysis (FRA) is an efficient method to examine the mechanical integrity of a power transformer. Different connection schemes can be implemented for measuring frequency responses. Moreover, the use of different terminating resistors and measurement impedances is possible. This paper investigates the influence of the measuring technique on the sensitivity of FRA traces. Consequently, different FRA traces are measured using two experimental windings, while specific mechanical changes, axial displacement, disc space variation, and radial deformation are applied to the windings. Six different resistors are utilized for termination and as the measurement impedance in the experimental setup. Two numerical indices are also employed to compare the sensitivity of the traces. The results of the sensitivity analysis are also validated with a circuit model of the windings. The points concluded can play a valuable role in defining the best FRA configuration for the detection of mechanical deformations.