A fast algorithm to remove decaying DC and harmonics for protective relaying

In protection relaying schemes of power system, the half-cycle discrete Fourier transform (HCDFT) is most widely used for fast computing the fundamental frequency component. However, when a fault occurs, both the voltage and current signals contain large harmonics and the decaying dc component during the fault duration. These abnormal components involved in measurements extremely postpone the convergent speed of conventional HCDFT algorithm. In order to overcome the above problems, this paper presents a novel algorithm, which combines the constrictive band-pass filter and HCDFT. The proposed algorithm effectively suppresses the abnormal frequency components and the fundamental frequency component can be achieved very fast, which only require half-cycle data window. The performance of this algorithm is proved by a lot of simulations with EMTP.