Exploring possibilities for characterization of power transformer insulation by frequency response analysis (FRA)

This paper explores the possibility for using frequency response analysis (FRA) technique to characterize the quality of transformer insulation. For this purpose, a single-phase and a three-phase lumped parameter circuit models were developed. The single-phase model represents a transformer without a laminated core, whereas the three-phase model represents a real transformer with core. Calculations of frequency dependent circuit parameters are presented and the effects imparted on the frequency response by different loss mechanisms (in insulation, in windings and in core) are discussed. The simulations are compared with results of measurements on real objects. It is shown that FRA could be used for insulation diagnostics if the measurements were of high enough quality.