Complete elimination of DC offset in current signals for relaying applications

This paper proposes a new method for exact estimation of DC offset in current signals such that DC offset can be completely eliminated for relaying applications. This new method, we called smart discrete Fourier transform (SDFT), based on discrete Fourier transform (DFT) keeps all advantages of DFT, and smartly avoids the defects resulting from frequency scales that can't match signal characteristics. Moreover, we use smoothing windows to filter noise in practice. The difference between SDFT and other methods, which use smoothing windows, is that SDFT can alleviate the difficulties of phase shift and amplitude decay caused by smoothing windows. Recursive and half-cycle computing can also be used in SDFT, so SDFT is very suitable for use in real-time. To validate the claimed benefits of SDFT, the performances of SDFT algorithm are demonstrated with the data generated by EMTP simulator. The simulation results are very encouraging.