Accurate Estimation of Transformer Winding Capacitances and Voltage Distribution Factor Using Driving Point Impedance Measurements

Abstract

This paper introduces an innovative methodology for precisely estimating winding capacitances ( $C_{s}$ and $C_{g}$ ) and the voltage distribution factor ( $\alpha $ ) in transformers using measured Driving Point Impedance (DPI) data. These parameters are critical for designing robust insulation systems and ensuring reliability during transient events. Unlike traditional approaches that rely on complex analytical models, impulse tests, or Finite Element Method (FEM) simulations, this method streamlines the estimation process by directly utilizing DPI measurements. Experimental validations across various winding configurations, including continuous and interleaved disc winding transformers, confirm the accuracy and versatility of this approach. The methodology presented offers substantial practical benefits for transformer condition monitoring. It facilitates efficient diagnostics of transformer deformations and impulse voltage distribution by estimating critical parameters from terminal measurements. The effect of noise on DPI data and the effectiveness of filtering techniques in enhancing parameter estimation accuracy have been rigorously analysed, demonstrating the method’s reliability. This approach is especially useful for newly constructed transformers that need design validation or for older transformers with incomplete design records. It provides a practical, efficient, and straightforward diagnostic solution, proving valuable for both researchers and engineers.

Keywords

• Capacitance estimation
• driving point impedance
• ladder network
• transformer diagnostics
• transformer windings
• voltage distribution factor