A non-iterative analytical approach for estimating series-capacitance in transformer windings solely from terminal measured frequency response data

Abstract

This paper presents a novel and non-iterative methodology for estimating the series capacitance ($C_s$) of power transformer windings based on terminal measurements through Frequency Response Analysis (FRA). Departing from conventional approaches that require detailed geometrical information, the proposed method utilizes practical terminal-based FRA, making $C_s$ estimation accessible to end-users. By categorizing the frequency response into low ($f_L$), mid ($f_M$), and high ($f_H$) frequency regions, targeted analysis is enabled. Extensive simulations and experimental studies on various windings, including single-layer, continuous disc, interleaved, and two-winding configurations, validate the method’s accuracy and versatility. The results show that estimated $C_s$ values closely match those from analytical calculations and Finite Element Method (FEM) simulations, with minimal errors. Key contributions of this work include a clear, step-by-step methodology for $C_s$ estimation through terminal-measured frequency response that eliminates the need for lookup tables, curve fitting, or model estimation, and demonstrates high accuracy under the impact of noise signals and transformer oil. The practical applicability of the proposed method is showcased through deformation diagnosis and voltage distribution analysis, highlighting its potential for widespread adoption in real-world scenarios.