Estimation of Series-and Shunt-Capacitances of a Practical Core-Type Power Transformer and Establishing Mathematical Relationship Thereof
Authors :- R Lekkireddy, K Shah, P Magdum, C Parekh
Publication :- IEEE Transactions on Industry Applications, 2025
The approach of synthesising a physically realisable ladder circuit model that accurately captures the electromagnetic coupling within a power transformer by characterising its high-frequency data is widely accepted. However, the challenging part is to estimate the inductances and capacitances pertaining to a practical power transformer, as the frequency response is influenced by the core, coupling between windings, the corresponding terminal connections and frequency of excitation. In this paper, a method to estimate the series- and shunt-capacitances of the test-winding in a practical transformer is reported without disassembling the inter-connected windings. The method involves representing a multi-winding transformer (1-Φ or 3-Φ) by electromagnetically coupled ladder circuits and suggesting a way to reduce complex circuits into a single, capacitive ladder circuit for the purpose of capacitance estimation. This task essentially involves proposing novel terminal connections, utilising on-tap voltage distribution, and identifying useful features of the driving-point impedance data so as to minimise the influence of the i) inductances, and interwinding capacitances, ii) non-tested windings, and core. Further, it is aimed to extract exact information pertaining to series-, shunt-capacitances through systematically derived formulas. The capability of the proposed method is initially demonstrated by simulation results followed by experimental measurements on 15 MVA, 66/11.55kV, Δ/Y, a practical 3-Φ unit of the transformer industry.