Analysis of Power Quality disturbances using wavelet packet transform

The term Power Quality (PQ) has gained lots of interest in the changed power distribution system scenario. The increased use of power electronic switches based equipment, nonlinear loads and the changed power system regulations has made PQ an important issue. The non-stationary PQ disturbances such as; voltage sag, swell, momentary interruptions, transients, along with the stationary harmonics have become more frequent in today´s power system. The conventionally used Fourier transform is found unsuitable for the analysis of non-stationary PQ disturbances. Different time -frequency analysis like, short time Fourier transform (STFT), discrete wavelet transform (DWT) and S- transform are in use for the analysis of non-stationary PQ disturbances. In this paper, the abilities of wavelet packet transform (WPT) are utilized to analyze different PQ disturbances. A new statistical variable is defined and computed for different PQ disturbances in order to analyze them. The newly defined variable is based on the average deviation of the WPT decompositions. The proposed variable is computed and analyzed for different variations of PQ disturbances to establish the usefulness of the WPT.