Detection of voltage sag/swell and harmonics using discrete S-transform

This paper shows the application of S-transform in identifying the voltage disturbances such as sag, interruption, swell and harmonics. S-transform is suitable for the analysis of power quality disturbances under noisy condition as it has excellent time-frequency resolution characteristics and has the ability to detect the disturbance correctly. Various voltage disturbances are generated as per IEEE Std. 1159 using MATLAB. S-transform analysis performed on these disturbance signals can identify the magnitude and duration of the disturbances. The effectiveness of the S-transform is shown for multiple sag/swell condition in the presence of transients or noise. Wavelet transform is also used for analysis and results are compared. Simulation results are also shown to identify both the harmonic magnitudes as well as their phase using S-transform analysis. Experimental verification has been performed with transmission line model connected to linear and non-linear loads and S-transform is used to detect and classify various voltage disturbances.