Abstract: Because of the limit of Heisenberg-Gabor inequality, the wavelet scalogram has low frequency concentration at small scales and low time concentration at large scales. In addition, misleading interference terms would appear in the scalogram at some conditions. All of those would influence scalogram analysis seriously. Reassignment method can improve the concentration of the scalogram and weaken the interference terms to certain extent, thus the readability of the scalogram can be improved. The experimental data of three kinds of faults：Rub-impact, coupling misalignment and the actual measurement data from a pumped storage power generator unit are analyzed by scalogram and reassigned scalogram, and the results by ordinary frequency analysis are also given. The comparison among three kinds of analysis results is carried out, and the comparison results indicate that the scalogram can not only reveal the time-frequency features of vibration signal but also extrude components of low energy. Therefore it is suitable to extract features of faults at early stage.

Key words: Fault diagnosis, Scalogram, Time-frequency analysis, Wavelet