Estimation of Series Capacitance of an Actual, Uniform, Single, Isolated Transformer Winding from Measured Driving Point Impedance Data

Abstract

The authors' research group established in 2011 that series capacitance of a single, uniform, isolated transformer winding was indirectly measurable via the frequency response measurement. The present work is a sequel and proposes a relatively simpler estimation method. It is based on exploiting a unique property of the first few coefficients (viz., s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sup> , s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> , and s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> terms) of the numerator and denominator polynomial of the driving point impedance (DPI) function, which is determined by curve-fitting the measured frequency response data. Essentially, the method solves a set of simultaneous equations which are formulated by equating pertinent coefficients of the fitted DPI(s) to the corresponding coefficients of the generalized expressions computed for an N-section ladder network. Going further, it is shown how the measured DPI data corresponding to the neutral-open and neutral-short cases can be usefully employed to cross-validate the estimated series capacitance. Experimental results on three different windings (viz., 2.2 kV/70 kVA continuous-disc, 33 kV/3.5 MVA continuous-disc, and a fully interleaved-disc) are presented to demonstrate the method's feasibility.