Detection of simultaneous transient and harmonics disturbances employing discrete wavelet transform

The increased use of non-linear loads, power electronic switches and changing regulations in today´s power distribution system has made power quality (PQ) an important concern. The various types of PQ disturbances are defined in IEEE standards 1159-2009 in terms of their frequency, magnitude and duration. The broadness of these definitions further makes it difficult to investigate these disturbances. Harmonics are among very common disturbances and are taken care of by Fourier transform based index; total harmonic disturbance (THD) very well. In this paper, discrete wavelet transform (DWT) based approach is presented to detect, localize and investigate the transient disturbances present in the PQ signals. The PQ signals carrying harmonics and transient disturbances simultaneously are specifically considered to verify the usefulness of proposed wavelet transform based method in compare to Fourier transform based index, THD.