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Mechanical vibrations analysis in direct drive using CWT with complex morlet wavelet

Łuczak Dominik

Power Electronics and Drives

2023

Vol. 8 (43)

65--73

Modern industrial process and household equipment more often use direct drives. According to European policy, Industry 4.0 and new Industry 5.0 need to undertake the effort required to ensure a sustainable, human-centric, and resilient European industry. One of the main problems of rotating machines is mechanical vibrations that can limit the lifetime of the final product or the machine in which they are applied. Therefore, analysis of vibration in electrical drives is crucial for appropriate maintenance of the machine. The present article undertakes an analysis of vibration measured at the laboratory stand with multiple dominant frequencies in the range 50-500 Hz. The fast Fourier transform (FFT) gives information about the frequency component without its time localisation. While the solution made available by the short-time Fourier transform (STFT) is able to overcome the problem of FFT, it still has limitations, particularly in terms of there being a lacuna in time and frequency localisation; accordingly, the need is felt for other methods that can give a good localisation in time and frequency. In the article, the continuous wavelet transform (CWT) was investigated, which requires selection of the wavelet function (kernel of transformation). The complex Morlet wavelet was selected with description of its central frequency and bandwidth. CWT and STFT time-frequency localisation capabilities were compared to investigate data registered from the direct-drive laboratory stand. CWT gives better frequency localisation than STFT even for the same frequency resolution. Vibration frequencies with near-locations were separated in CWT and STFT joined them into one wide pick. To ensure a good extraction of frequency features in electric drive systems, the author, based on analysing the results of the present study, recommends that CWT with complex Morlet wavelet be used instead of STFT.

Application of signal processing elements for the characteristics of acoustic emission pulses generated by partial discharges

Boczar T., Borucki S., Cichoń A., Lorenc M.

Molecular and Quantum Acoustics

2007

Vol. 28

23-38

The subject matter of this paper refers to the issues connected with the application of modern numerical methods in processing and analysis of the signals measured by the acoustic emission method (AE) during high-power experiments carried out in laboratory conditions in the setups modelling basic partial discharge forms (PDs). The detailed cognitive aim of the research work was determining the possibilities and the application range of the short time Fourier transform (STFT) and wavelet transform in the analysis of the AE pulses generated by basic PD forms that can occur in oil insulation systems of such appliances as transformers, measuring transformers, bushing insulators, switchgears, and power condensers. The time – frequency analysis was carried out for the particular PDs from the point of view of determining differences and indicating common features for the frequency structures determined, for the positive and negative voltage polarizations separately. The research concentrated mainly on the following types of PDs: point-plane, multipoint-plane, multipoint-plane with a layer of pressboard, surface, generated in gas bubbles and on the indeterminate-potential particles moving in oil. In calculations using wavelet transformations basic types of analyzing functions, the so-called basic wavelets, were applied. When determining amplitude spectrograms of the AE pulses measured various types of observation windows were used. Moreover, for the approximation runs determined and for the particular details the autocorrelation functions (ACF) were calculated, and the probability density functions (PDF) were calculated to determine statistical properties. Also, frequency spectrum runs for the AE pulses measured and the diagrams corresponding with the details analyzed, which visualize the size of energy transferred at the particular decomposition levels, were determined. The paper presents the results of measurements and analyses of the AE pulses generated by the PDs in oil in the multipoint-plane with a layer of pressboard system.