Practical considerations for recursive DFT implementation in numerical relays

In this paper, practical considerations for recursive Discrete Fourier Transform (DFT) implementation in numerical relays are presented. The DFT filter instabilities which would produce accumulated errors are emphasized. The aspects ruling error accumulation of the estimated magnitude and phase are highlighted. Novel solutions directed for the elimination of error accumulation are proposed and intensively tested. Digital signal processing (DSP) board based test set-up is utilized for the experimental verification. The paper results are valuable for the protection engineers particularly those concerned with the development and implementation of numerical relays.