Adaptive measuring algorithm suppressing a decaying DC component for digital protective relays

This paper presents a new adaptive phasor estimation algorithm for digital protective relaying. The algorithm is completely immune to an exponentially decaying dc component regardless of its initial magnitude and time constant. The algorithm is primarily intended for current signals and improves both magnitude and impedance measurements. The new technique is based on the recursive full-period Fourier filter with a separate adaptive function allowing for thorough rejection of the dc signal component. The comparative analysis of the algorithm, both analytical and by simulation, is included. The presented algorithm outperforms known measuring techniques including the digital mimic filtering broadly used in today's relays. (C) 2001 Elsevier Science B.V. All rights reserved.