Interest and utility of time frequency and time scale transforms in the partial discharges analysis

The development of time-frequency and time-scale transforms has progressed quickly for 20 years. This development and the progression of the numerical acquisition enable the utilization of these mathematical tools to analyze partial discharges (PD) in the induction motors insulation. Some papers have been written about the wavelet tools in order to analyze the partial discharges. This paper is a tutorial overview of the time frequency and time scale transforms applied to the PD analysis on the stators of the induction motors. In the first part two time-frequency transforms are introduced: short time Fourier transform and Wigner distribution. The mathematical tools for the implementation of the STFT are given. An example of extraction of a PD signal from numeric noise is given and its results discussed. In the second part the wavelets are presented on the same case study as for the time frequency transforms.