A Novel Generalized Analytic Expression of Power Transformer Equivalent RLC Model

The conversion of driving point impedance (DPI) data into a polynomial transfer function is a crucial task, which can be an effective tool to study the electromagnetic properties of the power transformer, and to provide a detection tool of transformer internal faults. This paper, presents a novel analytical approach to calculate the transfer function of the cascade model of parallel RLC cells equivalent to power transformer. However, in order to convert the impedance frequency response measurements data to a polynomial ratio, the numerator and denominator coefficients of the transfer function were determined according to the parameters identification of each cell of the RLC model from the FRA data tests obtained in a wide frequency range on each transformer phase. In addition, the developed transfer function in “s domain” has been generalized for an infinite number of cells of the adopted model. However, the transfer function of the RLC model cells has been proposed to meet the requirements of electromagnetic behavior analysis of transformer coils, and to provide a transformer internal faults diagnostic tool. The results of the proposed approach have been confronted to those obtained with experiment, it show a good concordance.