Parametric Evaluation for Comprehensive Fault Analysis in an Isolated HV-LV Winding Assembly Using Composite Frequency Response

Abstract

This paper presents new analytical expressions for equivalent inductance, total ground capacitance of individual HV and LV windings, and inter-winding capacitance within an isolated HV-LV winding assembly. These expressions directly link the parameters to the coefficients of five specific composite driving-point admittance functions, each tailored for specific terminal configuration within the assembly. A specific ratio of two coefficients from the fitted rational function for each measured magnitude response at the line-end of HV and LV windings directly yields the equivalent inductance of each winding. Similarly, three other specific ratios of two coefficients, extracted from fitted rational functions of three other measured responses (two from HV terminal and one from LV), yield three equations, solving which determines three capacitances (inter-winding and ground capacitances of HV and LV winding). More importantly, this method remains invariant for estimating these parameters of two windings both in healthy and fault-conditions. Changes in inductance or capacitance identify the faulty winding(s) and also assist in identifying the specific fault types. Experimental validation on a 33/11 kV winding assembly with core shows promising results for various faults viz. inter-turn shorting, disk-space variation, and radial deformation, demonstrating the method's accuracy in estimation and fault-analysis.