Online applications of wavelet transforms to power system relaying

Power system disturbances are normally subjected to transients and nonperiodic components which present a problem to the overall performance of protective relays. The use of traditional discrete Fourier transforms (DFTs) to extract the fundamental frequency components from the relaying signals is inappropriate to nonperiodic signals. A novel wavelet transform-based technique for power system relaying has been presented before, which has the ability to perform local analysis of relaying signals without losing the time-frequency information in the signal. This technique is considered to be straight-forward, fast, and adequate for online applications. In this paper, the theoretical background of the technique is presented. Then, the proposed method is described in detail. Finally, the effect of different parameters on the algorithm are examined in order to highlight its performance. It is found that the DWT is an excellent online tool for protective relaying applications using short data windows.