Identification of short duration power quality disturbances employing S-transform

Digital signal processing techniques based power quality analysis has attracted the attention of number of researchers. There are different time frequency techniques like short time Fourier transform (STFT), Continuous Wavelet transform (CWT) and S-transform used for the analysis of power quality disturbances. S-transform is a modified version of CWT with a phase correction. It offers a distinct advantage over the time frequency analysis techniques like CWT and STFT, by giving phase correction and better frequency localization in noisy environment too. In this paper, the identification and classification capabilities of S-transform based analysis is discussed. Short duration disturbances like voltage sag, voltage swell, momentary interruption, harmonics, capacitive switching transient, impulsive transient, transformer energizing are simulated using MATLAB and analyzed using S-transform. A combination of voltage swell, harmonics and capacitive switching events occurring simultaneously is also simulated and analyzed. A parameter based on the average of S magnitudes is calculated and its variations with respect to time for different power quality disturbances are analyzed for identification.