The Application Of Wavelet Packet In The Detection Of Voltage Sag

A wavelet packet transform method is proposed in the application of voltage sag detection. Firstly, analyzing three main kinds of reasons that cause voltage sags from the mechanism, such as system short-circuits, transformer exciting, and induction-motor starting. After Comparison of three filtering methods in the wavelet domain, the paper proposes an improved soft-threshold algorithm based on optimum wavelet packet basis for denoising, using the Garrote function to improve the threshold function, so as to the noise and unnecessary information can be deleted most correctly. Finally this thesis concerns with the classification of short-term power disturbances.Making the normalization distribution energy curve for classification of voltage sags, voltage swells, and voltage interruptions. Then, one-scale maxima modulus characteristics to distinction of pulse or oscillation. The accurate localization of voltage sag signal can be realized; its duration and amplitude can also be obtained. The simulation results have verified the validity of the proposed method.