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A simple method is described for constructing physically realizable driving-point impedance function from measured frequency response data (i.e., magnitude and phase) on a model winding and a transformer. A unique feature of the proposed method is that it ensures the constructed rational function is always positive-real, thereby guaranteeing synthesis of a physically realizable network every time. This feature could not always be guaranteed by earlier methods. Hence, it was a limitation. The proposed method is demonstrated on a single-layer model winding and the measured terminal characteristics is converted to a lumped parameter ladder network, since this representation is naturally suited to establish a physical mapping between the actual winding and synthesized circuit. So, the need to guarantee physical realizability is evident. Proceeding further, the terminal characteristics of a 315-kVA, 11/6.9-kV transformer is measured and a rational function representation is obtained. However, its realization as a coupled ladder network requires some more work to be done. In summary, it is believed that this proposal is a step towards providing a solution for localization of deformation in actual transformer windings.