Improvement of diagnostic methods for both power and distribution transformers is crucial considering the part they play in electrical networks as well as their cost. Transfer function based testing of transformers is one of the methods that has been introduced recently. This method enables the identification of winding deformations resulting from the short circuit currents and winding dislocations occurring during transportation, and can also be used to assess the state of electrical insulation. The methods of measurement of the transfer functions as well as the numerical simulations are aiming at determining the sensitivity of this method and to develop recognition criteria with regard to the type and range of the deformations.This paper presents a comparison of measurements and numerical simulation results of the transfer function performed on a medium-voltage transformer winding. A quantitative analysis of deformation detection and winding dislocation by means of the transfer function method is described.

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The transformer diagnostic methods are systematically being improved and extended due to growing requirements for reliability of power systems in terms of uninterrupted power supply and avoidance of blackouts. Those methods are also driven by longer lifetime of transformers and demand for reduction of transmission and distribution costs. Hence, the detection of winding faults in transformers, both in exploitation or during transportation is an important aspect of power transformer failure prevention. The frequency response analysis method (FRA), more and more frequently used in electric power engineering, has been applied for investigations and signature analysis based on the admittance and transfer function. The paper presents a novel approach to the identification of typical transformer winding problems such as axial or radial movements or turn-to-turn faults. The proposed transfer function discrimination (TFD) criteria are based on the derived transfer function ratios, manifesting higher sensitivity.

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