K Pourhossein - Department of Engineering , Islamic Azad University, Science and Research Branch, Tehran, Iran
G.B .Gharehpetian - Electrical Engineering Department, Amirkabir University of Technology, Tehran, Iran
E Rahimpour - ABB AG, Power Products Division, Transformers, R&D Department, Bad Honnef, Germany

Transfer Function (TF) method is a reliable tool to diagnose mechanical integrity of power transformers. TF method is based on the concept that mechanical changes in the windings cause changes in the parameters of the transformer and consequently a modification of its transfer function. Although TF is emerging as a powerful diagnostics technique, there is still no general guideline for interpreting measured TFs. In order to establish the differences between defected and intact case TFs, some numerical indices have been defined but none of them have regular change due to regular increase in defect extent. In this paper an adjustable index is applied on transformer TFs to construct a nearly linear mapping between any TF curve and its Axial Displacement (AD) extent. The results are verified using experiments and compared with two other common indices.

Power Transformer, Transfer Function, Axial Displacement, P-Norm