Three-Dimensional Approach to the Transfer Function in Transformer Windings and Its Application to the Interpretation of SFRA Results

Abstract

Power transformer integrity is critical for system reliability as mechanical winding deformations can alter electrical behavior. Sweep Frequency Response Analysis (SFRA) is widely used to detect such alterations; however, fault localization remains challenging due to the terminal nature of conventional measurements. This paper characterizes the distributed electromagnetic behavior of a transformer winding using spatially resolved transfer functions along its axial position. Controlled faults are introduced by modifying inter-disc capacitance, and magnitude and phase data are used to construct three-dimensional representations as a function of frequency and winding position. The proposed framework visualizes how localized perturbations redistribute modal energy within the winding. Selected diagnostic frequencies correspond to spatial electromagnetic modes, providing meaningful features for the classification model. A two-stage Support Vector Machine (SVM) is implemented to localize faults into predefined winding regions using only terminal measurements. The method achieves 94.4% overall classification accuracy. Results demonstrate that conventional SFRA data contain sufficient information for faulty localization when interpreted within a distributed-modal framework.