A measurement technique for quality control of windings for cast resin power transformers

The cast resin transformers are today used in a vast range of applications, as reliable answer for application concerning distribution systems, energy co-generation, rectification, traction and other special requirements. To increase the quality of the resin casting process, a research cooperation between the Department of Electrical and Information Engineering and Economics of the University of L'Aquila and the Bticino Legrand group has been started, with the main aim of developing a non- invasive and reliable measurement procedure, for a fast characterization and the identification of possible nonconformity for cast resin windings. The proposed procedure is based on the SFRA (Sweep Frequency Response Analysis), with some improvements for the correct evaluation of the correlation coefficients among different SFRA profiles. In this paper, the experimental results that have been obtained by applying the SFRA to windings of different sizes are presented, and some faults have been investigated.