Limits and usability of fast Fourier, Discrete wavelet and wavelet packet transforms applied at signals from a primary winding of a locomotive transformer

Abstract

Single phase currents and voltages were acquired from the primary winding of a locomotive transformer. Four operating regimes were considered (acceleration, running at constant speed, normal and respectively regenerative braking). 6 data sets consisting of 3 consecutive periods were considered as representative for this study and analyzed: one per each of the first 3 mentioned operating regimes and 3 for the regenerative braking. Fast Fourier Transform) and Wavelet Packet Transform were used to evaluate the harmonic spectra, Discrete Wavelet Transform was used to plot the instantaneous variations over frequency ranges of the distortions and all methods were used to evaluate the 3 major root mean square values (for fundamental frequency, for distorting residue and total). Total harmonic distortions were also evaluated. The results yielded by different methods were compared. A good convergence of methods was noticed. Explanations for the small differences are proposed.