Accurate estimation of series capacitance using the high-frequency lumped model of transformer winding from FRI data measurements: An indirect measurement procedure

• A novel indirect method for measuring the series capacitance of transformer windings has been proposed based on the equivalent circuit model, and it has proven to be feasible. • This methodology provides quick and precise results, regardless of the number of sections in the equivalent circuit. • The accuracy of this method has been evaluated against other measurement techniques. • The results demonstrate the effectiveness of the proposed approach and validate its reliability in diagnosing and monitoring transformer performance. Measuring the series capacitance of a transformer winding is a challenging task because it cannot be directly measured with standard devices. This paper presents an indirect method to determine this key parameter, relying on only two measurements: the equivalent capacitance and the total ground capacitance. These measurements are obtained directly from the frequency response impedance (FRI) data collected with the neutral open. The proposed methodology is based on an analytical relationship derived from a simplified lumped equivalent circuit for the transformer winding. This approach converts the lumped model capacitances into a second-degree polynomial function that varies with the unknown series capacitance. The method enables estimation of the winding's series capacitance, regardless of the number of sections in the equivalent circuit. It is applied practically to two different cases of transformer winding. Results showed that the method is both efficient and simple to implement, even in complex models. Comparisons with other estimation techniques confirmed its accuracy and effectiveness. Determining the series capacitance is essential for creating a comprehensive transformer winding model, as this parameter is vital for fault analysis and diagnosis.