Wavelet analysis of vibroacoustic signals registered during the transformer start-up

The subject matter of the paper focuses on evaluating the possible application of time-frequency analysis of vibroacoustic signals of transformers to assess the technical condition of their cores. The paper presents the results of the research related to development of a non-invasive diagnostic method for transformers´ magnetic circuit on the basis of measurements and analysis of mechanical vibrations registered during the start-up of the device under test. The results presented in the paper have been obtained during laboratory tests conducted on a 630 kVA unit with dry isolation. During the experiment conducted defects of the transformer core were modelled and then mechanical vibrations of the unit occurring during switching it into idle state were measured. The vibroacustic signals registered were digitally processed using the continuous wavelet transform (CWT). The method proposed by the authors, the so-called modified vibroacoustic method is based on measurements and time-frequency analysis of vibrations measured under transient operating conditions of the diagnosed transformer.