Digital protective relays use finite impulse response filters with sliding data windows for band-pass filtering of voltages and currents and measurement of phasors. Cosine, Fourier, and Walsh data windows are commonly used. In a digital relay, this signal is sampled N times per cycle. Thus the input is represented by Digital filters, such as those discussed in this paper, process the sampled data points, Sk, by multiplying each sample by a coefficient determined by the type of digital filter employed. This process is. Presented at the V Seminário Técnico de Proteção e Controle Curitiba, Brazil August 28–September 1, 1995 Previously presented at the IEEE WESCANEX 93 Communications, Computers and Power in the Modern Environment, May 1993, and 47th Annual Georgia Tech Protective Relaying Conference, April 1993. Edmund O. Schweitzer, III and Daqing Hou Schweitzer Engineering Laboratories, Inc. The highest frequency component determines the minimum sampling frequency Definition AF introduces certain phase shift (time delay) between its input and output signals.
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