An Improved Geometric Model for Constructing Frequency-Domain Spectroscopy of Nonuniform Aged Oil–Paper Insulation

Frequency-domain spectroscopy (FDS)-based methods are rarely reported for aging evaluation of nonuniform aged transformer insulation, in part due to the unavailability of the database. To address this issue, this work proposes an improved geometric model for constructing the FDS of oil–paper insulation under axial nonuniform aging. First, the mathematical expression of the model is theoretically derived based on the ${XY}$ model and nonuniform aging theory. Then, the composite structures for simulating the axial nonuniform aging are constructed in the lab condition, with the FDS data and degree of polymerization (DP) being collected by measurements. Finally, by comparing the FDS calculated by the proposed model and the collected data from the laboratory composite structure, the accuracy of the improved geometric model has been preliminarily verified. The obtained results indicate that the mean relative error (MRE) is less than 14.40%. In that respect, this work is expected to provide an effective tool for constructing the FDS database of nonuniform aged oil–paper insulation.