Removal of DC offset in current and voltage signals using a novel Fourier filter algorithm

Protecting transmission lines frequently involves adopting distance relays, Protective relays must filter their inputs to reject unwanted quantities a nd retain signal quantities of interest. Accuracy and convergent speed of f ilter algorithm are essential for protective relays, A widely applied filte r algorithm, the discrete Fourier transform (DFT) can easily erase harmonie s using simple calculation, However, the voltage and current signals contai n large harmonics and de offset during the fault interval. The de offset he avily influences the precision and convergence speed of fundamental frequen cy signal from DFT. In this investigation, we present a novel Fourier algor ithm to remove the de offset in a voltage or current signal. Applying full- cycle DFT (FCDFT) requires one cycle plus two samples to calculate and comp ensate for the de offset. Half-cycle DFT (HCDFT) only requires half of a cy cle plus two or three samples to accomplish the algorithm when the input si gnal has no even order harmonics, Adopting the proposed algorithm in distan ce relays effectively suppresses the de offset and quickly decomposes the a ccurate fundamental frequency components.