Investigating the performance of discrete wavelet transform for phasor estimation in digital relays

Digital relays traditionally use phasor estimation techniques based on the digital Fourier transform (DFT) and its variants. In recent literature, it is claimed that discrete wavelet transform (DWT) based filter performs better than traditional filters for phasor estimation. However, these claims are not well supported by sufficiently detailed analysis. This paper presents a detailed analysis to verify the claim. Both synthetic waveforms and fault waveforms simulated with PSCAD/EMTDC are used. Effect of the decaying dc offset on filter performance is studied in detail. Performances of DFT, Cosine, and least-error-square (LES) algorithms are compared with DWT algorithm.